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1
Djordjevic, Ivan B. "LDPC-Coded Optical Coherent State Quantum Communications". IEEE Photonics Technology Letters 19, n. 24 (dicembre 2007): 2006–8. http://dx.doi.org/10.1109/lpt.2007.909688.
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Sidhu, Jasminder S., Michael S. Bullock, Saikat Guha e Cosmo Lupo. "Linear optics and photodetection achieve near-optimal unambiguous coherent state discrimination". Quantum 7 (31 maggio 2023): 1025. http://dx.doi.org/10.22331/q-2023-05-31-1025.
Abstract (sommario):
Coherent states of the quantum electromagnetic field, the quantum description of ideal laser light, are prime candidates as information carriers for optical communications. A large body of literature exists on their quantum-limited estimation and discrimination. However, very little is known about the practical realizations of receivers for unambiguous state discrimination (USD) of coherent states. Here we fill this gap and outline a theory of USD with receivers that are allowed to employ: passive multimode linear optics, phase-space displacements, auxiliary vacuum modes, and on-off photon detection. Our results indicate that, in some regimes, these currently-available optical components are typically sufficient to achieve near-optimal unambiguous discrimination of multiple, multimode coherent states.
3
Эскандери, М. М., Д. Б. Хорошко e С. Я. Килин. "Безошибочное различение когерентных состояний двухмодового оптического поля". Журнал технической физики 128, n. 8 (2020): 1171. http://dx.doi.org/10.21883/os.2020.08.49716.83-20.
Abstract (sommario):
The procedure of a quantum measurement, the unambiguous state discrimination, is studied for the case of four two-mode coherent states of the optical field, interesting for information transmission via an optical communication channel. It is shown that a complex conjugation of the amplitude of one of the modes results in a better distinguishability of the states. An interferometric scheme is suggested for unambiguous discrimination of such states and the probability of successful discrimination is found. Applications of the considered state set are discussed for quantum cryptography, quantum teleportation and optical communications with a high level of loss.
4
PIRANDOLA, STEFANO. "A QUANTUM TELEPORTATION GAME". International Journal of Quantum Information 03, n. 01 (marzo 2005): 239–43. http://dx.doi.org/10.1142/s0219749905000815.
Abstract (sommario):
We investigate a game where a sender (Alice) teleports coherent states to two receivers (Bob and Charlie) through a tripartite Gaussian state. The aim of the receivers is to optimize their teleportation fidelities by means of local operations and classical communications. We show that a non-cooperative strategy corresponding to the standard telecloning protocol can be outperformed by a cooperative strategy which gives rise to a novel (cooperative) telecloning protocol.
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Meddour, H., Sh Askar, S. Dehraj, F. Al-dolaimy, B. S. Abdullaeva, A. Alsaalamy, M. N. Fenjan, A. Alawadi, S. H. Kareem e D. Thabit. "Efficient two-dimensional Fraunhofer diffraction pattern via electron spin coherence". Laser Physics 33, n. 11 (6 ottobre 2023): 116003. http://dx.doi.org/10.1088/1555-6611/acfd9a.
Abstract (sommario):
Abstract In this letter, we have discussed the two-dimensional diffraction pattern via electron spin coherence in a GaAs quantum dot. Impulsive stimulated Raman excitation utilizing coherent optical fields is employed for the purpose of regulating the electron spin coherence within a charged ensemble of GaAs quantum dots, by means of an intermediate charged exciton (trion) state. We show that for the coupling two-dimensional standing wave (SW) field in the x and y directions, the two-dimensional Fraunhofer pattern can be formed for a weak probe light. By using the experimental parameters and controlling the Rabi frequency of the SW field and relative phase between applied lights, the symmetry and asymmetry diffraction pattern are obtained for the weak probe light due to the four-wave mixing mechanism. Our proposed model may have potential applications in high-capacity optical communications and quantum information technologies.
6
Becerra, F. E., J. Fan e A. Migdall. "Photon number resolution enables quantum receiver for realistic coherent optical communications". Nature Photonics 9, n. 1 (17 novembre 2014): 48–53. http://dx.doi.org/10.1038/nphoton.2014.280.
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El-Nahal, Fady. "Coherent 16 Quadrature Amplitude Modulation (16QAM) Optical Communication Systems". Photonics Letters of Poland 10, n. 2 (30 giugno 2018): 57. http://dx.doi.org/10.4302/plp.v10i2.809.
Abstract (sommario):
Coherent optical fiber communications for data rates of 100Gbit/s and beyond have recently been studied extensively primarily because high sensitivity of coherent receivers could extend the transmission distance. Spectrally efficient modulation techniques such as M-ary quadrature amplitude modulation (M-QAM) can be employed for coherent optical links. The integration of multi-level modulation formats based on coherent technologies with wavelength-division multiplexed (WDM) systems is key to meet the aggregate bandwidth demand. This paper reviews coherent 16 quadrature amplitude modulation (16QAM) systems to scale the network capacity and maximum reach of current optical communication systems to accommodate traffic growth. Full Text: PDF ReferencesK. Kikuchi, "Fundamentals of Coherent Optical Fiber Communications", J. Lightwave Technol., vol. 34, no. 1, pp. 157-179, 2016. CrossRef S. Tsukamoto, D.-S. Ly-Gagnon, K. Katoh, and K. Kikuchi, "Coherent Demodulation of 40-Gbit/s Polarization-Multiplexed QPSK Signals with16-GHz Spacing after 200-km Transmission", Proc. OFc, Paper PDP29, (2005). DirectLink K. Kikuchi, "Coherent Optical Communication Technology", Proc. OFC, Paper Th4F.4, (2015). CrossRef J. M. Kahn and K.-P. Ho, "Spectral efficiency limits and modulation/detection techniques for DWDM systems", IEEE J. Sel. Topics Quantum Electron., vol. 10, no. 2, pp. 259–272, (2004). CrossRef S. Tsukamoto, K. Katoh, and K. Kikuchi, "Coherent demodulation of optical multilevel phase-shift-keying signals using homodyne detection and digital signal processing", IEEE Photon. Technol. Lett., vol. 18, no. 10, pp. 1131–1133, (2006). CrossRef Y. Mori, C. Zhang, K. Igarashi, K. Katoh, and K. Kikuchi, "Unrepeated 200-km transmission of 40-Gbit/s 16-QAM signals using digital coherent receiver", Opt. Exp., vol. 17, no. 32, pp. 1435–1441, (2009). CrossRef H. Nakashima, Et al., "Digital Nonlinear Compensation Technologies in Coherent Optical Communication Systems", Proc. OFC, Paper W1G.5, (2017). CrossRef S. J. Savory, "Digital filters for coherent optical receivers", Opt. Exp., vol. 16, no. 2, pp. 804–817, (2008). CrossRef D. S. Millar, T. Koike-Akino, S. Ö. Arık, K. Kojima, K. Parsons, T. Yoshida, and T. Sugihara, "High-dimensional modulation for coherent optical communications systems", Opt. Express, vol. 22, no. 7, pp 8798-8812, (2014). CrossRef R. Griffin and A. Carter, "Optical differential quadrature phase-shift key (oDQPSK) for high capacity optical transmission", Proc. OFC, Paper WX6, (2002). DirectLink K. Kikuchi, "Digital coherent optical communication systems: fundamentals and future prospects", IEICE Electron. Exp., vol. 8, no. 20, pp. 1642–1662, (2011). CrossRef F. Derr, "Optical QPSK transmission system with novel digital receiver concept", Electron Lett., vol. 27, no. 23, pp. 2177–2179, (1991). CrossRef R. No’e, "Phase noise tolerant synchronous QPSK receiver concept with digital I&Q baseband processing", Proc. OECC, Paper 16C2-5, (2004). DirectLink D.-S. Ly-Gagnon, S. Tsukamoto, K. Katoh, and K. Kikuchi, "Coherent detection of optical quadrature phase-shift keying signals with carrier phase estimation", J. Lightw. Technol., vol. 24, no. 1, pp. 12–21, (2006). CrossRef M. Taylor, "Coherent detection method using DSP for demodulation of signal and subsequent equalization of propagation impairments", IEEE Photon. Technol. Lett., vol. 16, no. 2, pp. 674–676, (2004). CrossRef S. Tsukamoto, K. Katoh, and K. Kikuchi, "Unrepeated transmission of 20-Gb/s optical quadrature phase-shift-keying signal over 200-km standard single-mode fiber based on digital processing of homodyne-detected signal for Group-velocity dispersion compensation", IEEE Photon. Technol. Lett., vol. 18, no. 9, pp. 1016–1018, (2006). CrossRef S. Tsukamoto, Y. Ishikawa, and K. Kikuchi, "Optical Homodyne Receiver Comprising Phase and Polarization Diversities with Digital Signal Processing", Proc. ECOC, Paper Mo4.2.1, (2006). CrossRef K. Kikuchi and S. Tsukamoto, "Evaluation of Sensitivity of the Digital Coherent Receiver", J. Lightw. Technol., vol. 20, no. 13, pp. 1817–1822, (2008). CrossRef S. Ishimura and K. Kikuchi, "Multi-dimensional Permutation Modulation Aiming at Both High Spectral Efficiency and High Power Efficiency", Proc. OFC/NFOEC, Paper M3A.2, (2014). CrossRef F. I. El-Nahal and A. H. M. Husein, "Radio over fiber access network architecture employing RSOA with downstream OQPSK and upstream re-modulated OOK data", (Optik) Int. J. Light Electron Opt., vol. 123, no. 14, pp: 1301-1303, (2012). CrossRef T. Koike-Akino, D. S. Millar, K. Kojima, and K. Parsons, "Eight-Dimensional Modulation for Coherent Optical Communications", Proc. ECOC, Paper Tu.3.C.3, (2013). DirectLink B. Sklar, Digital communications: Fundamentals and Applications, Prentice-Hall, (2001).
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AWSCHALOM, DAVID D. "CONTROLLING SPIN COHERENCE WITH SEMICONDUCTOR NANOSTRUCTURES". International Journal of Modern Physics B 22, n. 01n02 (20 gennaio 2008): 111–12. http://dx.doi.org/10.1142/s0217979208046165.
Abstract (sommario):
We present two emerging opportunities for manipulating and communicating coherent spin states in semiconductors. First, we show that semiconductor microcavities offer unique means of controlling light-matter interactions in confined geometries, resulting in a wide range of applications in optical communications and inspiring proposals for quantum information processing and computational schemes. Studies of spin dynamics in microcavities — a new and promising research field — have revealed novel effects such as polarization beats, stimulated spin scattering, and giant Faraday rotation. Here, we study the electron spin dynamics in optically-pumped GaAs microdisk lasers with quantum wells and interface-fluctuation quantum dots in the active region. In particular, we examine how the electron spin dynamics are modified by the stimulated emission in the disks, and observe an enhancement of the spin coherence time when the optical excitation is in resonance with a high quality ( Q ~ 5000) lasing mode.1 This resonant enhancement, contrary to expectations from the observed trend in the carrier recombination time, is then manipulated by altering the cavity design and dimensions. In analogy to devices based on excitonic coherence, this ability to engineer coherent interactions between electron spins and photons may provide novel pathways towards spin dependent quantum optoelectronics. In a second example, the nitrogen-vacancy (N-V) center in diamond has garnered interest as a room-temperature solid-state system not only for exploring electronic and nuclear spin phenomena but also as a candidate for spin-based quantum information processing. Spin coherence times of up to 50 microseconds have been reported for ensembles of N-V centers and a two-qubit gate utilizing the electron spin of a N-V center and the nuclear spin of a nearby C-13 atom has been demonstrated. Here, we present experiments using angle-resolved magneto-photoluminescence microscopy to investigate anisotropic spin interactions of single N-V centers in diamond at room temperature.2 Negative peaks in the photoluminescence intensity are observed as a function of both magnetic field magnitude and angle, and can be explained by coherent spin precession and anisotropic relaxation at spin-level anticrossings. Additionally, precise field alignment with the symmetry axis of a single N-V center reveals the resonant magnetic dipolar coupling of a single "bright" electron spin of an N-V center to small numbers of "dark" spins of nitrogen defects in its immediate vicinity, which are otherwise undetected by photoluminescence. Most recently, we are exploring the possibility of utilizing this magnetic dipole coupling between bright and dark spins to couple two spatially separated single N-V center spins by means of intermediate nitrogen spins. Note from Publisher: This article contains the abstract only.
9
Holevo, A. S., e M. E. Shirokov. "Mutual and coherent information for infinite-dimensional quantum channels". Problems of Information Transmission 46, n. 3 (settembre 2010): 201–18. http://dx.doi.org/10.1134/s0032946010030014.
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Lu, Z. G., J. R. Liu, Y. X. Mao, K. Zeb, G. C. Liu, J. Webber, M. Rahim et al. "Quantum dot multi-wavelength lasers for Tbit/s coherent communications and 5G wireless networks -INVITED". EPJ Web of Conferences 238 (2020): 01003. http://dx.doi.org/10.1051/epjconf/202023801003.
Abstract (sommario):
We will present the design, growth, fabrication, electronic control and packaging of the InAs/InP quantum dot (QD) multi-wavelength lasers (MWLs) developed by AEP of NRC in Canada. Their key technical specifications include L-I-V curves, optical and RF beating spectra, relative intensity noise (RIN), and optical phase noise of each individual wavelength channel, as well as timing jitter are investigated. Data bandwidth transmission capacity of 5.376 Tbit/s and 10.3 Tbit/s respectively in the PAM-4 and 16-QAM modulation formats are demonstrated by only using a single QD MWL chip. We have also developed a novel monolithic InAs/InP QD dual-wavelength (DW) DFB laser as a compact optical beat source to generate millimeter-wave (MMW) signals. Because of using a common cavity, highly coherent and correlated optical modes with optical linewidth as low as 15.83 kHz, spectrally pure MMW signals around 46.8 GHz with a linewidth down to 26.1 kHz were experimentally demonstrated. By using this QD DW-DFB laser, a 1Gbaud (2Gbps) MMW over-fiber transmission link is demonstrated with PAM-4 signals. The results show that the demonstrated device is suitable for high speed high capacity MMW fiber-wireless integrated fronthaul of 5G networks.
11
Morshnev, Sergey K., e A. V. Fantsesson. "Erratum: Coherent fiber-optic communications (review) [Sov. J. Quantum Electron. 15, 1183-1197 (September 1985)]". Soviet Journal of Quantum Electronics 15, n. 12 (31 dicembre 1985): 1662. http://dx.doi.org/10.1070/qe1985v015n12abeh008103.
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Bonaldi, Michele, Antonio Borrielli, Giovanni Di Giuseppe, Nicola Malossi, Bruno Morana, Riccardo Natali, Paolo Piergentili, Pasqualina Maria Sarro, Enrico Serra e David Vitali. "Low Noise Opto-Electro-Mechanical Modulator for RF-to-Optical Transduction in Quantum Communications". Entropy 25, n. 7 (19 luglio 2023): 1087. http://dx.doi.org/10.3390/e25071087.
Abstract (sommario):
In this work, we present an Opto-Electro-Mechanical Modulator (OEMM) for RF-to-optical transduction realized via an ultra-coherent nanomembrane resonator capacitively coupled to an rf injection circuit made of a microfabricated read-out able to improve the electro-optomechanical interaction. This device configuration can be embedded in a Fabry–Perot cavity for electromagnetic cooling of the LC circuit in a dilution refrigerator exploiting the opto-electro-mechanical interaction. To this aim, an optically measured steady-state frequency shift of 380 Hz was seen with a polarization voltage of 30 V and a Q-factor of the assembled device above 106 at room temperature. The rf-sputtered titanium nitride layer can be made superconductive to develop efficient quantum transducers.
13
Dey, Sanjib, Andreas Fring e Véronique Hussin. "Nonclassicality versus entanglement in a noncommutative space". International Journal of Modern Physics B 31, n. 01 (10 gennaio 2017): 1650248. http://dx.doi.org/10.1142/s0217979216502489.
Abstract (sommario):
Nonclassicality is an interesting property of light having applications in many different contexts of quantum optics, quantum information and computation. Nonclassical states produce substantial amount of reduced noise in optical communications. Furthermore, they often behave as sources of entangled quantum states, which are the most elementary requirement for quantum teleportation. We study various nonclassical properties of coherent states and Schrödinger cat states in a setting of noncommutative space resulting from the generalized uncertainty relation, first, in a complete analytical fashion and, later, by computing their entanglement entropies, which in turn provide supporting arguments behind our analytical results. By using standard theoretical frameworks, they are shown to produce considerably improved squeezing and nonclassicality and, hence, significantly higher amount of entanglement in comparison to the usual quantum mechanical models. Both the nonclassicality and the entanglement can be enhanced further by increasing the noncommutativity of the underlying space. In addition, we find as a by-product some rare explicit minimum uncertainty quadrature and number squeezed states, i.e., ideal squeezed states.
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Wang, Michelle, Cooper Doyle, Bryn Bell, Matthew J. Collins, Eric Magi, Benjamin J. Eggleton, Mordechai Segev e Andrea Blanco-Redondo. "Topologically protected entangled photonic states". Nanophotonics 8, n. 8 (9 maggio 2019): 1327–35. http://dx.doi.org/10.1515/nanoph-2019-0058.
Abstract (sommario):
AbstractEntangled multiphoton states lie at the heart of quantum information, computing, and communications. In recent years, topology has risen as a new avenue to robustly transport quantum states in the presence of fabrication defects, disorder, and other noise sources. Whereas topological protection of single photons and correlated photons has been recently demonstrated experimentally, the observation of topologically protected entangled states has thus far remained elusive. Here, we experimentally demonstrate the topological protection of spatially entangled biphoton states. We observe robustness in crucial features of the topological biphoton correlation map in the presence of deliberately introduced disorder in the silicon nanophotonic structure, in contrast with the lack of robustness in non-topological structures. The topological protection is shown to ensure the coherent propagation of the entangled topological modes, which may lead to robust propagation of quantum information in disordered systems.
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Lib, Ohad, e Yaron Bromberg. "Thermal biphotons". APL Photonics 7, n. 3 (1 marzo 2022): 031301. http://dx.doi.org/10.1063/5.0085342.
Abstract (sommario):
The observation of the Hanbury Brown and Twiss (HBT) effect with thermal light marked the birth of quantum optics. All the thermal sources considered to date did not feature quantum signatures of light, as they consisted of independent emitters that emit uncorrelated photons. Here, we propose and demonstrate an incoherent light source based on phase-randomized spatially entangled photons, which we coin thermal biphotons. We show that in contrast to thermal light, the width of the HBT peak for thermal biphotons is determined by their correlations, leading to violation of the Siegert relation and breakdown of the speckle-fluctuations interpretation. We further provide an alternative interpretation of the results by drawing a connection between the HBT effect and coherent backscattering of light. Finally, we discuss the role of spatial entanglement in the observed results, deriving a relation between the Schmidt number and the degree of violation of the Siegert relation under the double-Gaussian approximation of spontaneous parametric down conversion. Our work reflects new insights on the coherence properties of thermal light in the presence of entanglement, paving the way for entanglement certification using disorder averaged measurements.
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Gulbahar, Burhan. "Theory of Quantum Path Entanglement and Interference with Multiplane Diffraction of Classical Light Sources". Entropy 22, n. 2 (21 febbraio 2020): 246. http://dx.doi.org/10.3390/e22020246.
Abstract (sommario):
Quantum history states were recently formulated by extending the consistent histories approach of Griffiths to the entangled superposition of evolution paths and were then experimented with Greenberger–Horne–Zeilinger states. Tensor product structure of history-dependent correlations was also recently exploited as a quantum computing resource in simple linear optical setups performing multiplane diffraction (MPD) of fermionic and bosonic particles with remarkable promises. This significantly motivates the definition of quantum histories of MPD as entanglement resources with the inherent capability of generating an exponentially increasing number of Feynman paths through diffraction planes in a scalable manner and experimental low complexity combining the utilization of coherent light sources and photon-counting detection. In this article, quantum temporal correlation and interference among MPD paths are denoted with quantum path entanglement (QPE) and interference (QPI), respectively, as novel quantum resources. Operator theory modeling of QPE and counterintuitive properties of QPI are presented by combining history-based formulations with Feynman’s path integral approach. Leggett–Garg inequality as temporal analog of Bell’s inequality is violated for MPD with all signaling constraints in the ambiguous form recently formulated by Emary. The proposed theory for MPD-based histories is highly promising for exploiting QPE and QPI as important resources for quantum computation and communications in future architectures.
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Abbas, A. H., e Ivan S. Maksymov. "Reservoir Computing Using Measurement-Controlled Quantum Dynamics". Electronics 13, n. 6 (21 marzo 2024): 1164. http://dx.doi.org/10.3390/electronics13061164.
Abstract (sommario):
Physical reservoir computing (RC) is a machine learning algorithm that employs the dynamics of a physical system to forecast highly nonlinear and chaotic phenomena. In this paper, we introduce a quantum RC system that employs the dynamics of a probed atom in a cavity. The atom experiences coherent driving at a particular rate, leading to a measurement-controlled quantum evolution. The proposed quantum reservoir can make fast and reliable forecasts using a small number of artificial neurons compared with the traditional RC algorithm. We theoretically validate the operation of the reservoir, demonstrating its potential to be used in error-tolerant applications, where approximate computing approaches may be used to make feasible forecasts in conditions of limited computational and energy resources.
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Perez-Leija, Armando, Hector Moya-Cessa, Francisco Soto-Eguibar, Omar Aguilar-Loreto e Demetrios N. Christodoulides. "Erratum to “Classical analogues to quantum nonlinear coherent states in photonic lattices” [Optics Communications 284 (2011) 1833–1836]". Optics Communications 285, n. 9 (maggio 2012): 2483. http://dx.doi.org/10.1016/j.optcom.2012.01.016.
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Hu, Guangchong, Rose L. Ahlefeldt, Gabriele G. de Boo, Alexey Lyasota, Brett C. Johnson, Jeffrey C. McCallum, Matthew J. Sellars, Chunming Yin e Sven Rogge. "Single site optical spectroscopy of coupled Er3+ ion pairs in silicon". Quantum Science and Technology 7, n. 2 (9 marzo 2022): 025019. http://dx.doi.org/10.1088/2058-9565/ac56c7.
Abstract (sommario):
Abstract Individual optical emitters coupled via coherent interactions are attractive qubits for quantum communications applications. Here, we present the first study of single pairs of interacting rare earth ions and determine the interactions between ions in the pair with high resolution. We identify two examples of Er3+ pair sites in Er implanted Si and characterise the interactions using optical Zeeman spectroscopy. We identify one pair as two Er3+ ions in sites of at least C 2 symmetry coupled via a large, 200 GHz, Ising-like spin interaction in both optical ground and excited states. The high measurement resolution allows non-Ising contributions to the interaction of < 1 % to be observed, attributed to site distortion. By bringing two optical transitions into resonance with a magnetic field, we observe a 0.8 GHz optical interaction of unusual magnetic-dipole/electric-dipole character with strong polarization selection rules. We discuss the use of this type of strongly coupled, field-tunable rare earth pair system for quantum processing.
20
Li, Fei, Hai Zhong, Yijun Wang, Ye Kang, Duan Huang e Ying Guo. "Performance Analysis of Continuous-Variable Quantum Key Distribution with Multi-Core Fiber". Applied Sciences 8, n. 10 (17 ottobre 2018): 1951. http://dx.doi.org/10.3390/app8101951.
Abstract (sommario):
Performance analysis of continuous-variable quantum key distribution (CVQKD) has been one of the focuses of quantum communications. In this paper, we propose an approach to enhancing the secret rate of CVQKD with the multi-core fiber (MCF) system that transmits multiple spatial modes simultaneously. The excess noise contributed by the inter-core crosstalk between cores can be effectively suppressed by quantum channel wavelength management, leading to the performance improvement of the MCF-based CVQKD system. In the security analysis, we perform numerical simulations for the Gaussian-modulated coherent state CVQKD protocol, considering simultaneously the extra insert loss of fan-in/fan-out (FIFO), which is the extra optical device that should be used at the input and the output of the fiber. Simulation results show that the performance of the one-way and two-way protocols for each core are slightly degraded because of the insert loss of the FIFO, but the total secret key rate can be increased, whereas the performance of the measurement-device-independent CVQKD protocol will be degraded due to the effect of the insert loss of the FIFO. These results may provide theoretical foundation for the space-division multiplexing CVQKD system.
21
Okada, Takumi, Kazuhiro Komori, Xue-Lun Wang, Mutsuo Ogura e Noriaki Tsurumachi. "Coherent control of semiconductor quantum wire by high-resolution and stable Michelson interferometer". Electronics and Communications in Japan 94, n. 5 (25 aprile 2011): 25–32. http://dx.doi.org/10.1002/ecj.10238.
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Viti, Leonardo, Alisson R. Cadore, Xinxin Yang, Andrei Vorobiev, Jakob E. Muench, Kenji Watanabe, Takashi Taniguchi, Jan Stake, Andrea C. Ferrari e Miriam S. Vitiello. "Thermoelectric graphene photodetectors with sub-nanosecond response times at terahertz frequencies". Nanophotonics 10, n. 1 (10 luglio 2020): 89–98. http://dx.doi.org/10.1515/nanoph-2020-0255.
Abstract (sommario):
AbstractUltrafast and sensitive (noise equivalent power <1 nW Hz−1/2) light-detection in the terahertz (THz) frequency range (0.1–10 THz) and at room-temperature is key for applications such as time-resolved THz spectroscopy of gases, complex molecules and cold samples, imaging, metrology, ultra-high-speed data communications, coherent control of quantum systems, quantum optics and for capturing snapshots of ultrafast dynamics, in materials and devices, at the nanoscale. Here, we report room-temperature THz nano-receivers exploiting antenna-coupled graphene field effect transistors integrated with lithographically-patterned high-bandwidth (∼100 GHz) chips, operating with a combination of high speed (hundreds ps response time) and high sensitivity (noise equivalent power ≤120 pW Hz−1/2) at 3.4 THz. Remarkably, this is achieved with various antenna and transistor architectures (single-gate, dual-gate), whose operation frequency can be extended over the whole 0.1–10 THz range, thus paving the way for the design of ultrafast graphene arrays in the far infrared, opening concrete perspective for targeting the aforementioned applications.
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Ben Amar Baranga, Andrei, Gennady A. Koganov, David Levron, Gabriel Bialolenker e Reuben Shuker. "Quantum Applications of an Atomic Ensemble Inside a Laser Cavity". Photonics 11, n. 1 (2 gennaio 2024): 46. http://dx.doi.org/10.3390/photonics11010046.
Abstract (sommario):
Many quantum device signals are proportional to the number of the participating atoms that take part in the detection devices. Among these are optical magnetometers, atomic clocks, quantum communications and atom interferometers. One way to enhance the signal-to-noise ratio is to introduce atom entanglement that increases the signal in a super-radiant-like effect. A coherent em field inside a laser cavity is suggested to achieve atoms’ correlation/entanglement. This may also play an important role in the basic quantum arena of many-body physics. An initial novel experiment to test the realization of atoms’ correlation is described here. A Cs optical magnetometer is used as a tool to test the operation of a cell-in-cavity laser and its characteristics. A vapor cell is inserted into an elongated external cavity of the pump laser in Littrow configuration. Higher atom polarization and reduced laser linewidth are obtained leading to better magnetometer sensitivity and signal-to-noise ratio. The Larmor frequency changes of the Free Induction Decay of optically pumped Cs atomic polarization in the ambient earth magnetic field at room temperature is measured. Temporal changes in the magnetic field of less than 10 pT/√Hz are measured. The first-order dependence of the magnetic field on temperature and temperature gradients is eliminated, important in many practical applications. Single and gradiometric magnetometer configurations are presented.
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Kuang, Randy, e Adrian Chan. "Quantum encryption in phase space with displacement operators". EPJ Quantum Technology 10, n. 1 (29 giugno 2023). http://dx.doi.org/10.1140/epjqt/s40507-023-00183-0.
Abstract (sommario):
AbstractIn photonic computing, the quantum systems consist of coherent states and squeezed coherent states. Common quantum gates found in these systems are: phase shift, displacement, and squeezing gates. These gates are all unitary and reversible. Outside of quantum systems, coherent states also plays a significant role in coherent optical communications with speeds of hundreds of gigabits per second. Secure optical communications is generally implemented at the data layer with classical symmetric encryption such as Advanced Standard Encryption or AES. This inevitably allows any wiretapping to capture the transmitted data either in the plaintext mode or in the encrypted ciphertext mode in the optical infrastructure. The recent and rapid developments in Quantum computing further lift up the need for quantum secure communications in the optical infrastructure. This paper proposes a novel quantum encryption in the coherent optical domain utilizing a displacement operator and implementing with IQ-MZM optical modules, called Quantum Encryption in Phase Space or QEPS. The communication peers share a secret used to seed cryptographic pseudo random number generators to produce a synchronized random number at both the transmitter and receiver. The synchronized random numbers are used to establish displacement operators to encrypt the coherent states at the transmission and decrypt the cipher coherent states at the receiver. Therefore, malicious parties tapping along the fibre line would not extract the message in transit from optical domain due to a high Bit Error Rate or BER. The optimal displacement operator is split into a standard 16-QAM and a random phase shift operator to enhance the transmission security. We analysis the transmission security with the wiretap channel model for semantic security. We have simulated the QEPS encryption and decryption for two data modulation schemes: QPSK and 16-QAM over 80 km for transmission speeds of 56 Gbps for QPSK and 112 Gbps for 16-QAM.
25
Liu, Yulong, Qichun Liu, Huanying Sun, Mo Chen, Shuaipeng Wang e Tiefu Li. "Coherent memory for microwave photons based on long-lived mechanical excitations". npj Quantum Information 9, n. 1 (11 agosto 2023). http://dx.doi.org/10.1038/s41534-023-00749-x.
Abstract (sommario):
AbstractMechanical resonators, due to their capability to host ultralong-lived phonon modes, are particularly attractive for quantum state storage and as memory elements in conjunction with quantum computing and communication networks. Here we demonstrate absorptive-type coherent memory based on long-lived mechanical excitations. The itinerant coherent microwave field is captured, stored, and retrieved from a mechanical memory oscillator which is pre-cooled to the ground state. The phase space distribution allows us to distinguish between coherent and thermal components and study their evolution as a function of storage time. Our device exhibits attractive functions with an energy decay time of T1 = 15.9 s, a thermal decoherence rate of Γth = 2.85 Hz, and acquires less than one quantum noise during the τcoh = 55.7 ms storage period. We demonstrate that both the amplitude and phase information of microwave coherent states can be recovered, indicating the coherence of our memory device. These results suggest that high-Q mechanical resonators and long coherence time phonons could be ideal candidates for the construction of long-lived and on-demand microwave quantum memories.
26
DiMario, M. T., e F. E. Becerra. "Demonstration of optimal non-projective measurement of binary coherent states with photon counting". npj Quantum Information 8, n. 1 (18 luglio 2022). http://dx.doi.org/10.1038/s41534-022-00595-3.
Abstract (sommario):
AbstractQuantum state discrimination is a central problem in quantum measurement theory, with applications spanning from quantum communication to computation. Typical measurement paradigms for state discrimination involve a minimum probability of error or unambiguous discrimination with a minimum probability of inconclusive results. Alternatively, an optimal inconclusive measurement, a non-projective measurement, achieves minimal error for a given inconclusive probability. This more general measurement encompasses the standard measurement paradigms for state discrimination and provides a much more powerful tool for quantum information and communication. Here, we experimentally demonstrate the optimal inconclusive measurement for the discrimination of binary coherent states using linear optics and single-photon detection. Our demonstration uses coherent displacement operations based on interference, single-photon detection, and fast feedback to prepare the optimal feedback policy for the optimal non-projective quantum measurement with high fidelity. This generalized measurement allows us to transition among standard measurement paradigms in an optimal way from minimum error to unambiguous measurements for binary coherent states. As a particular case, we use this general measurement to implement the optimal minimum error measurement for phase-coherent states, which is the optimal modulation for communications under the average power constraint. Moreover, we propose a hybrid measurement that leverages the binary optimal inconclusive measurement in conjunction with sequential, unambiguous state elimination to realize higher dimensional inconclusive measurements of coherent states.
27
Opatrný, Tomáš, Šimon Bräuer, Abraham G. Kofman, Avijit Misra, Nilakantha Meher, Ofer Firstenberg, Eilon Poem e Gershon Kurizki. "Nonlinear coherent heat machines". Science Advances 9, n. 1 (6 gennaio 2023). http://dx.doi.org/10.1126/sciadv.adf1070.
Abstract (sommario):
We propose heat machines that are nonlinear, coherent, and closed systems composed of few field (oscillator) modes. Their thermal-state input is transformed by nonlinear Kerr interactions into nonthermal (non-Gaussian) output with controlled quantum fluctuations and the capacity to deliver work in a chosen mode. These machines can provide an output with strongly reduced phase and amplitude uncertainty that may be useful for sensing or communications in the quantum domain. They are experimentally realizable in optomechanical cavities where photonic and phononic modes are coupled by a Josephson qubit or in cold gases where interactions between photons are transformed into dipole-dipole interacting Rydberg atom polaritons. This proposed approach is a step toward the bridging of quantum and classical coherent and thermodynamic descriptions.
28
Park, Kimin, Jacob Hastrup, Jonas Schou Neergaard-Nielsen, Jonatan Bohr Brask, Radim Filip e Ulrik L. Andersen. "Slowing quantum decoherence of oscillators by hybrid processing". npj Quantum Information 8, n. 1 (15 giugno 2022). http://dx.doi.org/10.1038/s41534-022-00577-5.
Abstract (sommario):
AbstractQuantum information encoded into the superposition of coherent states is an illustrative representation of practical applications of macroscopic quantum coherence possessing. However, these states are very sensitive to energy loss, losing their non-classical aspects of coherence very rapidly. An available deterministic strategy to slow down this decoherence process is to apply a Gaussian squeezing transformation prior to the loss as a protective step. Here, we propose a deterministic hybrid protection scheme utilizing strong but feasible interactions with two-level ancillas immune to spontaneous emission. We verify the robustness of the scheme against the dephasing of qubit ancilla. Our scheme is applicable to complex superpositions of coherent states in many oscillators, and remarkably, the robustness to loss is enhanced with the amplitude of the coherent states. This scheme can be realized in experiments with atoms, solid-state systems, and superconducting circuits.
29
Clivati, Cecilia, Alice Meda, Simone Donadello, Salvatore Virzì, Marco Genovese, Filippo Levi, Alberto Mura et al. "Coherent phase transfer for real-world twin-field quantum key distribution". Nature Communications 13, n. 1 (10 gennaio 2022). http://dx.doi.org/10.1038/s41467-021-27808-1.
Abstract (sommario):
AbstractQuantum mechanics allows distribution of intrinsically secure encryption keys by optical means. Twin-field quantum key distribution is one of the most promising techniques for its implementation on long-distance fiber networks, but requires stabilizing the optical length of the communication channels between parties. In proof-of-principle experiments based on spooled fibers, this was achieved by interleaving the quantum communication with periodical stabilization frames. In this approach, longer duty cycles for the key streaming come at the cost of a looser control of channel length, and a successful key-transfer using this technique in real world remains a significant challenge. Using interferometry techniques derived from frequency metrology, we develop a solution for the simultaneous key streaming and channel length control, and demonstrate it on a 206 km field-deployed fiber with 65 dB loss. Our technique reduces the quantum-bit-error-rate contributed by channel length variations to <1%, representing an effective solution for real-world quantum communications.
30
Nicolas, L., M. Businger, T. Sanchez Mejia, A. Tiranov, T. Chanelière, E. Lafitte-Houssat, A. Ferrier, P. Goldner e M. Afzelius. "Coherent optical-microwave interface for manipulation of low-field electronic clock transitions in 171Yb3+:Y2SiO5". npj Quantum Information 9, n. 1 (3 marzo 2023). http://dx.doi.org/10.1038/s41534-023-00687-8.
Abstract (sommario):
AbstractThe coherent interaction of solid-state spins with both optical and microwave fields provides a platform for a range of quantum technologies, such as quantum sensing, microwave-to-optical quantum transduction and optical quantum memories. Rare-earth ions with electronic spins are interesting in this context. In this work, we use a loop-gap microwave resonator to coherently drive optical and microwave clock transitions simultaneously in a 171Yb3+:Y2SiO5 crystal, achieving a Rabi frequency of 0.56 MHz at 2.497 GHz over a 1-cm long crystal. Furthermore, we provide insights into the spin dephasing at very low fields, showing that superhyperfine-induced collapse of the Hahn echo plays an important role. Our calculations and measurements reveal that the effective magnetic moment can be manipulated in 171Yb3+:Y2SiO5, which suppresses the superhyperfine interaction at the clock transition. At a doping concentration of 2 ppm and 3.4 K, we achieve spin coherence time of 10.0 ± 0.4 ms.
31
Hernández-Gómez, Santiago, Stefano Gherardini, Alessio Belenchia, Andrea Trombettoni, Mauro Paternostro e Nicole Fabbri. "Experimental signature of initial quantum coherence on entropy production". npj Quantum Information 9, n. 1 (11 settembre 2023). http://dx.doi.org/10.1038/s41534-023-00738-0.
Abstract (sommario):
AbstractWe report on the experimental quantification of the contribution to non-equilibrium entropy production stemming from the quantum coherence content in the initial state of a qubit exposed to both coherent driving and dissipation. Our experimental demonstration builds on the exquisite experimental control of the spin state of a nitrogen-vacancy defect in diamond and is underpinned, theoretically, by the formulation of a generalized fluctuation theorem designed to track the effects of quantum coherence. Our results provide significant evidence of the possibility to pinpoint the genuinely quantum mechanical contributions to the thermodynamics of non-equilibrium quantum processes in an open quantum systems scenario.
32
Sidhu, Jasminder S., Thomas Brougham, Duncan McArthur, Roberto G. Pousa e Daniel K. L. Oi. "Finite key performance of satellite quantum key distribution under practical constraints". Communications Physics 6, n. 1 (10 agosto 2023). http://dx.doi.org/10.1038/s42005-023-01299-6.
Abstract (sommario):
AbstractGlobal-scale quantum communication networks will require efficient long-distance distribution of quantum signals. While optical fibre communications are range-limited due to exponential losses in the absence of quantum memories and repeaters, satellites enable intercontinental quantum communications. However, the design of satellite quantum key distribution (SatQKD) systems has unique challenges over terrestrial networks. The typical approach to modelling SatQKD has been to estimate performances with a fully optimised protocol parameter space and with few payload and platform resource limitations. Here, we analyse how practical constraints affect the performance of SatQKD for the Bennett-Brassard 1984 (BB84) weak coherent pulse decoy state protocol with finite key size effects. We consider engineering limitations and trade-offs in mission design including limited in-orbit tunability, quantum random number generation rates and storage, and source intensity uncertainty. We quantify practical SatQKD performance limits to determine the long-term key generation capacity and provide performance benchmarks to support the design of upcoming missions.
33
Kumar, Niraj, Eleni Diamanti e Iordanis Kerenidis. "Efficient quantum communications with coherent state fingerprints over multiple channels". Physical Review A 95, n. 3 (31 marzo 2017). http://dx.doi.org/10.1103/physreva.95.032337.
34
Harney, Cillian, e Stefano Pirandola. "End-to-end capacities of imperfect-repeater quantum networks". Quantum Science and Technology, 23 giugno 2022. http://dx.doi.org/10.1088/2058-9565/ac7ba0.
Abstract (sommario):
Abstract The optimal performance of a communication network is limited not only by the quality of point-to-point channels but by the efficacy of its constituent technologies. Understanding the limits of quantum networks requires an understanding of both the ultimate capacities of quantum channels and the efficiency of imperfect quantum repeaters. In this work, using a recently developed node-splitting technique that introduces internal losses and noise into repeater devices, we present achievable end-to-end rates for noisy-repeater quantum networks. These are obtained by extending the coherent and reverse coherent information (single channel capacity lower bounds) into end-to-end capacity lower bounds, both in the context of single-path and multi-path routing. These achievable rates are completely general and apply to networks composed of arbitrary channels arranged in general topologies. Through this general formalism, we show how tight upper-bounds can also be derived by supplementing appropriate single-edge capacity bounds. As a result, we develop tools that provide tight performance bounds for quantum networks constituent of channels whose capacities are not exactly known and reveal critical network properties which are necessary for high-rate quantum communications. This permits the investigation of pertinent classes of quantum networks with realistic technologies; qubit amplitude damping networks and bosonic thermal-loss networks.
35
Wang, Chien-An, Corentin Déprez, Hanifa Tidjani, William I. L. Lawrie, Nico W. Hendrickx, Amir Sammak, Giordano Scappucci e Menno Veldhorst. "Probing resonating valence bonds on a programmable germanium quantum simulator". npj Quantum Information 9, n. 1 (17 giugno 2023). http://dx.doi.org/10.1038/s41534-023-00727-3.
Abstract (sommario):
AbstractSimulations using highly tunable quantum systems may enable investigations of condensed matter systems beyond the capabilities of classical computers. Quantum dots and donors in semiconductor technology define a natural approach to implement quantum simulation. Several material platforms have been used to study interacting charge states, while gallium arsenide has also been used to investigate spin evolution. However, decoherence remains a key challenge in simulating coherent quantum dynamics. Here, we introduce quantum simulation using hole spins in germanium quantum dots. We demonstrate extensive and coherent control enabling the tuning of multi-spin states in isolated, paired, and fully coupled quantum dots. We then focus on the simulation of resonating valence bonds and measure the evolution between singlet product states which remains coherent over many periods. Finally, we realize four-spin states with s-wave and d-wave symmetry. These results provide means to perform non-trivial and coherent simulations of correlated electron systems.
36
Wang, Nan, Zhi-Bo Yang, Shi-Yan Li, Ting-Ting Dong e Ai-Dong Zhu. "Parametric controllable one-way quantum steering induced by four-wave mixing in cavity magnonics". EPJ Quantum Technology 10, n. 1 (19 maggio 2023). http://dx.doi.org/10.1140/epjqt/s40507-023-00172-3.
Abstract (sommario):
AbstractQuantum steering plays a crucial role in quantum communication and one-way quantum computation. Here, we study quantum steering between two magnon modes in a cavity-magnonics system by applying a two-photon drive field to the microwave cavity. The two magnon modes are entangled and the one-way steering can be implemented when the four-wave mixing is triggered. Different from most schemes that use the dissipation of the system to control quantum steering, in our scheme the one-way steering can be modulated on demand by adjusting the coherent coupling ratio between the two magnons and the cavity, which provides a flexible and feasible way in experiments. We also reveal that the directionality of quantum steering is related to the mode populations, i.e., the mode with a larger population dominants the steering. Our study has high manipulability and may provide a promising platform for one-way quantum computing and communications based on macroscopic entanglement state.
37
Misra, Avijit, Pritam Chattopadhyay, Anatoly Svidzinsky, Marlan O. Scully e Gershon Kurizki. "Black-hole powered quantum coherent amplifier". npj Quantum Information 10, n. 1 (28 marzo 2024). http://dx.doi.org/10.1038/s41534-024-00817-w.
Abstract (sommario):
AbstractAtoms falling into a black hole (BH) through a cavity are shown to enable coherent amplification of light quanta powered by the BH-gravitational vacuum energy. This process can harness the BH energy towards useful purposes, such as propelling a spaceship trapped by the BH. The process can occur via transient amplification of a signal field by falling atoms that are partly excited by Hawking radiation reflected by an orbiting mirror. In the steady-state regime of thermally equilibrated atoms that weakly couple to the field, this amplifier constitutes a BH-powered quantum heat engine. The envisaged effects substantiate the thermodynamic approach to BH acceleration radiation.
38
Zhou, Chao, Pinlei Lu, Matthieu Praquin, Tzu-Chiao Chien, Ryan Kaufman, Xi Cao, Mingkang Xia et al. "Realizing all-to-all couplings among detachable quantum modules using a microwave quantum state router". npj Quantum Information 9, n. 1 (6 giugno 2023). http://dx.doi.org/10.1038/s41534-023-00723-7.
Abstract (sommario):
AbstractOne of the primary challenges in realizing large-scale quantum processors is the realization of qubit couplings that balance interaction strength, connectivity, and mode confinement. Moreover, it is very desirable for the device elements to be detachable, allowing components to be built, tested, and replaced independently. In this work, we present a microwave quantum state router, centered on parametrically driven, Josephson-junction based three-wave mixing, that realizes all-to-all couplings among four detachable quantum modules. We demonstrate coherent exchange among all four communication modes, with an average full-iSWAP time of 764 ns and average inferred inter-module exchange fidelity of 0.969, limited by mode coherence. We also demonstrate photon transfer and pairwise entanglement between module qubits, and parallel operation of simultaneous iSWAP exchange across the router. Our router-module architecture serves as a prototype of modular quantum computer that has great potential for enabling flexible, demountable, large-scale quantum networks of superconducting qubits and cavities.
39
Rengaswamy, Narayanan, Kaushik P. Seshadreesan, Saikat Guha e Henry D. Pfister. "Belief propagation with quantum messages for quantum-enhanced classical communications". npj Quantum Information 7, n. 1 (15 giugno 2021). http://dx.doi.org/10.1038/s41534-021-00422-1.
Abstract (sommario):
AbstractFor space-based laser communications, when the mean photon number per received optical pulse is much smaller than one, there is a large gap between communications capacity achievable with a receiver that performs individual pulse-by-pulse detection, and the quantum-optimal “joint-detection receiver” that acts collectively on long codeword-blocks of modulated pulses; an effect often termed “superadditive capacity”. In this paper, we consider the simplest scenario where a large superadditive capacity is known: a pure-loss channel with a coherent-state binary phase-shift keyed (BPSK) modulation. The two BPSK states can be mapped conceptually to two non-orthogonal states of a qubit, described by an inner product that is a function of the mean photon number per pulse. Using this map, we derive an explicit construction of the quantum circuit of a joint-detection receiver based on a recent idea of “belief-propagation with quantum messages” (BPQM). We quantify its performance improvement over the Dolinar receiver that performs optimal pulse-by-pulse detection, which represents the best “classical” approach. We analyze the scheme rigorously and show that it achieves the quantum limit of minimum average error probability in discriminating 8 (BPSK) codewords of a length-5 binary linear code with a tree factor graph. Our result suggests that a BPQM receiver might attain the Holevo capacity of this BPSK-modulated pure-loss channel. Moreover, our receiver circuit provides an alternative proposal for a quantum supremacy experiment, targeted at a specific application that can potentially be implemented on a small, special-purpose, photonic quantum computer capable of performing cat-basis universal qubit logic.
40
Singh, Satvik, e Nilanjana Datta. "Detecting positive quantum capacities of quantum channels". npj Quantum Information 8, n. 1 (5 maggio 2022). http://dx.doi.org/10.1038/s41534-022-00550-2.
Abstract (sommario):
AbstractDetermining whether a noisy quantum channel can be used to reliably transmit quantum information is a challenging problem in quantum information theory. This is because it requires computation of the channel’s coherent information for an unbounded number of copies of the channel. In this paper, we devise an elementary perturbative technique to solve this problem in a wide variety of circumstances. Our analysis reveals that a channel’s ability to transmit information is intimately connected to the relative sizes of its input, output, and environment spaces. We exploit this link to develop easy tests which can be used to detect positivity of quantum channel capacities simply by comparing the channels’ input, output, and environment dimensions. Several noteworthy examples, such as the depolarizing and transpose-depolarizing channels (including the Werner-Holevo channel), dephasing channels, generalized Pauli channels, multi-level amplitude damping channels, and (conjugate) diagonal unitary covariant channels, serve to aptly exhibit the utility of our method. Notably, in all these examples, the coherent information of a single copy of the channel turns out to be positive.
41
Sidhu, Jasminder S., Thomas Brougham, Duncan McArthur, Roberto G. Pousa e Daniel K. L. Oi. "Finite key effects in satellite quantum key distribution". npj Quantum Information 8, n. 1 (16 febbraio 2022). http://dx.doi.org/10.1038/s41534-022-00525-3.
Abstract (sommario):
AbstractGlobal quantum communications will enable long-distance secure data transfer, networked distributed quantum information processing, and other entanglement-enabled technologies. Satellite quantum communication overcomes optical fibre range limitations, with the first realisations of satellite quantum key distribution (SatQKD) being rapidly developed. However, limited transmission times between satellite and ground station severely constrains the amount of secret key due to finite-block size effects. Here, we analyse these effects and the implications for system design and operation, utilising published results from the Micius satellite to construct an empirically-derived channel and system model for a trusted-node downlink employing efficient Bennett-Brassard 1984 (BB84) weak coherent pulse decoy states with optimised parameters. We quantify practical SatQKD performance limits and examine the effects of link efficiency, background light, source quality, and overpass geometries to estimate long-term key generation capacity. Our results may guide design and analysis of future missions, and establish performance benchmarks for both sources and detectors.
42
Senica, Urban, Andres Forrer, Tudor Olariu, Paolo Micheletti, Sara Cibella, Guido Torrioli, Mattias Beck, Jérôme Faist e Giacomo Scalari. "Planarized THz quantum cascade lasers for broadband coherent photonics". Light: Science & Applications 11, n. 1 (24 dicembre 2022). http://dx.doi.org/10.1038/s41377-022-01058-2.
Abstract (sommario):
AbstractRecently, there has been a growing interest in integrated THz photonics for various applications in communications, spectroscopy and sensing. We present a new integrated photonic platform based on active and passive elements integrated in a double-metal, high-confinement waveguide layout planarized with a low-loss polymer. An extended top metallization keeps waveguide losses low while improving dispersion, thermal and RF properties, as it enables to decouple the design of THz and microwave cavities. Free-running on-chip quantum cascade laser combs spanning 800 GHz, harmonic states with over 1.1 THz bandwidth and RF-injected broadband incoherent states spanning over nearly 1.6 THz are observed using a homogeneous quantum-cascade active core. With a strong external RF drive, actively mode-locked pulses as short as 4.4 ps can be produced, as measured by SWIFTS. We demonstrate as well passive waveguides with low insertion loss, enabling the tuning of the laser cavity boundary conditions and the co-integration of active and passive elements on the same THz photonic chip.
43
Wu, Yi-Hsien, Leon C. Camenzind, Akito Noiri, Kenta Takeda, Takashi Nakajima, Takashi Kobayashi, Chien-Yuan Chang et al. "Hamiltonian phase error in resonantly driven CNOT gate above the fault-tolerant threshold". npj Quantum Information 10, n. 1 (11 gennaio 2024). http://dx.doi.org/10.1038/s41534-023-00802-9.
Abstract (sommario):
AbstractBecause of their long coherence time and compatibility with industrial foundry processes, electron spin qubits are a promising platform for scalable quantum processors. A full-fledged quantum computer will need quantum error correction, which requires high-fidelity quantum gates. Analyzing and mitigating gate errors are useful to improve gate fidelity. Here, we demonstrate a simple yet reliable calibration procedure for a high-fidelity controlled-rotation gate in an exchange-always-on Silicon quantum processor, allowing operation above the fault-tolerance threshold of quantum error correction. We find that the fidelity of our uncalibrated controlled-rotation gate is limited by coherent errors in the form of controlled phases and present a method to measure and correct these phase errors. We then verify the improvement in our gate fidelities by randomized benchmark and gate-set tomography protocols. Finally, we use our phase correction protocol to implement a virtual, high-fidelity, controlled-phase gate.
44
Di Paolo, Agustin, Thomas E. Baker, Alexandre Foley, David Sénéchal e Alexandre Blais. "Efficient modeling of superconducting quantum circuits with tensor networks". npj Quantum Information 7, n. 1 (27 gennaio 2021). http://dx.doi.org/10.1038/s41534-020-00352-4.
Abstract (sommario):
AbstractWe use a tensor network method to compute the low-energy excitations of a large-scale fluxonium qubit up to a desired accuracy. We employ this numerical technique to estimate the pure-dephasing coherence time of the fluxonium qubit due to charge noise and coherent quantum phase slips from first principles, finding an agreement with previously obtained experimental results. By developing an accurate single-mode theory that captures the details of the fluxonium device, we benchmark the results obtained with the tensor network for circuits spanning a Hilbert space as large as 15180. Our algorithm is directly applicable to the wide variety of circuit-QED systems and may be a useful tool for scaling up superconducting quantum technologies.
45
Miguel-Ramiro, J., A. Pirker e W. Dür. "Genuine quantum networks with superposed tasks and addressing". npj Quantum Information 7, n. 1 (7 settembre 2021). http://dx.doi.org/10.1038/s41534-021-00472-5.
Abstract (sommario):
AbstractWe show how to make quantum networks, both standard and entanglement-based, genuine quantum by providing them with the possibility of handling superposed tasks and superposed addressing. This extension of their functionality relies on a quantum control register, which specifies not only the task of the network, but also the corresponding weights in a coherently superposed fashion. Although adding coherent control to classical tasks, such as sending or measuring—or not doing so—is in general impossible, we introduce protocols that are able to mimick this behavior under certain conditions. We achieve this by always performing the classical task, either on the desired state or a properly chosen dummy state. We provide several examples, and show that externally controlling quantum superposition of tasks offers additional possibilities and advantages over usually considered single functionality. For instance, superpositions of different target state configurations shared among different nodes of the network can be prepared, or quantum information can be sent among a superposition of different paths or to different destinations.
46
He, Jiangbo, Dong Pan, Mingli Liu, Zhaozheng Lyu, Zhongmou Jia, Guang Yang, Shang Zhu et al. "Quantifying quantum coherence of multiple-charge states in tunable Josephson junctions". npj Quantum Information 10, n. 1 (2 gennaio 2024). http://dx.doi.org/10.1038/s41534-023-00798-2.
Abstract (sommario):
AbstractCoherence and tunneling play central roles in quantum phenomena. In a tunneling event, the time that a particle spends inside the barrier has been fiercely debated. This problem becomes more complex when tunneling repeatedly occurs back and forth, and when involving many particles. Here we report the measurement of the coherence time of various charge states tunneling in a nanowire-based tunable Josephson junction; including single charges, multiple charges, and Cooper pairs. We studied all the charge tunneling processes using Landau-Zener-Stückelberg-Majorana (LZSM) interferometry, and observed high-quality interference patterns under a microwave drive. In particular, the coherence time of the charge states tunneling back and forth was extracted from the interference fringes in Fourier space. In addition, our measurements show the break-up of Cooper pairs, from a macroscopic quantum coherent state to individual particle states. Besides the fundamental research interest, our results also establish LZSM interferometry as a powerful technique to explore the coherence time of charges in hybrid devices.
47
Deplano, Quentin, Philippe Tamarat, Brahim Lounis e Jean-Baptiste Trebbia. "Sub-nanosecond coherent optical manipulation of a single aromatic molecule at cryogenic temperature". AVS Quantum Science 5, n. 4 (1 dicembre 2023). http://dx.doi.org/10.1116/5.0180689.
Abstract (sommario):
Single molecules trapped in the solid state at liquid helium temperatures are promising quantum emitters for the development of quantum technologies owing to their remarkable photostability and their lifetime-limited optical coherence time of the order of 10 ns. The coherent preparation of their electronic state requires resonant excitation with a Rabi period much shorter than their optical coherence time. Sculpting the optical excitation with sharp edges and a high on–off intensity ratio (∼3 × 105) from a single-frequency laser beam, we demonstrate sub-nanosecond drive of a single dibenzanthanthrene molecule embedded in a naphthalene matrix at 3.2 K, over more than 17 Rabi periods. With pulses tailored for a half-Rabi period, the electronic excited state is prepared with fidelity as high as 0.97. Using single-molecule Ramsey spectroscopy, we prove up to 5 K that the optical coherence lifetime remains at its fundamental upper limit set by twice the excited-state lifetime, making single molecules suitable for quantum bit manipulations under standard cryogen-free cooling technologies.
48
Vahapoglu, E., J. P. Slack-Smith, R. C. C. Leon, W. H. Lim, F. E. Hudson, T. Day, J. D. Cifuentes et al. "Coherent control of electron spin qubits in silicon using a global field". npj Quantum Information 8, n. 1 (4 novembre 2022). http://dx.doi.org/10.1038/s41534-022-00645-w.
Abstract (sommario):
AbstractSilicon spin qubits promise to leverage the extraordinary progress in silicon nanoelectronic device fabrication over the past half century to deliver large-scale quantum processors. Despite the scalability advantage of using silicon technology, realising a quantum computer with the millions of qubits required to run some of the most demanding quantum algorithms poses several outstanding challenges, including how to control many qubits simultaneously. Recently, compact 3D microwave dielectric resonators were proposed as a way to deliver the magnetic fields for spin qubit control across an entire quantum chip using only a single microwave source. Although spin resonance of individual electrons in the globally applied microwave field was demonstrated, the spins were controlled incoherently. Here we report coherent Rabi oscillations of single electron spin qubits in a planar SiMOS quantum dot device using a global magnetic field generated off-chip. The observation of coherent qubit control driven by a dielectric resonator establishes a credible pathway to achieving large-scale control in a spin-based quantum computer.
49
CAO, Qian, Pengkun Zheng e Qiwen Zhan. "Vectorial sculpturing of spatiotemporal wavepackets". APL Photonics, 15 agosto 2022. http://dx.doi.org/10.1063/5.0107411.
Abstract (sommario):
Spatiotemporal vectorial pulse shaping can produce ultrafast optical pulses that enable unprecedented coherent control for light matter interactions. Traditional pulse shaper produces ultrafast pulses with scalar programmable waveforms for various quantum control applications. However, quantum systems are three dimensional in nature thus the interactions are inevitability vectorial. Existing polarization pulse shaping techniques, which are often difficult to align and cumbersome to handle, can only produce dynamic polarization modulation in the temporal domain. Through simply introducing a quarter-wave plate in a pulse shaper using a two-dimensional spatial light modulator, we show that wavepackets with much more sophisticated spatiotemporal vectorial structures such as spatiotemporal spin grating, spatiotemporal spin lattice and spatiotemporally twisting polarization can be generated, significantly expanding our ability in coherently controlling light matter interactions that may find broad applications.
50
Lu, Zhenguo, Jiaren Liu, Youxin Mao, Khan Zeb, Guocheng Liu, Philip J. Poole, John Weber et al. "Quantum dash multi-wavelength lasers for Tbit/s coherent communications and 5G wireless networks". Journal of the European Optical Society-Rapid Publications 17, n. 1 (13 giugno 2021). http://dx.doi.org/10.1186/s41476-021-00156-9.
Abstract (sommario):
AbstractWe report on the design, growth, fabrication, and performance of InAs/InP quantum dash (QD) multi-wavelength lasers (MWLs) developed by the National Research Council (NRC) Canada. The key technical specifications investigated include optical and RF beating spectra, relative intensity noise (RIN), and optical phase noise of each individual wavelength channel. Data bandwidth transmission capacity of 5.376 Tbit/s and 10.8 Tbit/s respectively in the PAM-4 and 16-QAM modulation formats are demonstrated using only a single C-band QD 34.2-GHz MWL chip. We have also developed a monolithic InAs/InP QD dual-wavelength (DW) DFB laser as a compact optical beat source to generate millimeter-wave (MMW) signals. Due to the common cavity, highly coherent and correlated optical modes with optical linewidth as low as 15.83 kHz, spectrally pure MMW signals around 46.8 GHz with a linewidth down to 26.1 kHz were experimentally demonstrated. By using this QD DW-DFB laser, a one GBaud (2 Gbps) MMW over-fiber transmission link is demonstrated with PAM-4 signals. The results show that the demonstrated device is suitable for high speed high capacity MMW fiber-wireless integrated fronthaul of 5G networks.