Journal articles on the topic 'Spin qubit'
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1
WU, YIN-ZHONG, WEI-MIN ZHANG, and CHOPIN SOO. "QUANTUM COMPUTATION BASED ON ELECTRON SPIN QUBITS WITHOUT SPIN-SPIN INTERACTION." International Journal of Quantum Information 03, supp01 (November 2005): 155–62. http://dx.doi.org/10.1142/s0219749905001341.
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Using electron spin states in a unit cell of three semiconductor quantum dots as qubit states, a scalable quantum computation scheme is advocated without invoking qubit-qubit interactions. Single electron tunneling technology and coherent quantum-dot cellular automata architecture are used to generate an ancillary charge entangled state which is then converted into spin entangled state. Without using charge measurement and ancillary qubits, we demonstrate universal quantum computation based on free electron spin and coherent quantum-dot cellular automata.
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Ferraro, Elena, and Marco De Michielis. "Bandwidth-Limited and Noisy Pulse Sequences for Single Qubit Operations in Semiconductor Spin Qubits." Entropy 21, no. 11 (October 26, 2019): 1042. http://dx.doi.org/10.3390/e21111042.
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Spin qubits are very valuable and scalable candidates in the area of quantum computation and simulation applications. In the last decades, they have been deeply investigated from a theoretical point of view and realized on the scale of few devices in the laboratories. In semiconductors, spin qubits can be built confining the spin of electrons in electrostatically defined quantum dots. Through this approach, it is possible to create different implementations: single electron spin qubit, singlet–triplet spin qubit, or a three-electron architecture, e.g., the hybrid qubit. For each qubit type, we study the single qubit rotations along the principal axis of Bloch sphere including the mandatory non-idealities of the control signals that realize the gate operations. The realistic transient of the control signal pulses are obtained by adopting an appropriate low-pass filter function. In addition. the effect of disturbances on the input signals is taken into account by using a Gaussian noise model.
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Takeda, Kenta, Akito Noiri, Takashi Nakajima, Takashi Kobayashi, and Seigo Tarucha. "Quantum error correction with silicon spin qubits." Nature 608, no. 7924 (August 24, 2022): 682–86. http://dx.doi.org/10.1038/s41586-022-04986-6.
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AbstractFuture large-scale quantum computers will rely on quantum error correction (QEC) to protect the fragile quantum information during computation1,2. Among the possible candidate platforms for realizing quantum computing devices, the compatibility with mature nanofabrication technologies of silicon-based spin qubits offers promise to overcome the challenges in scaling up device sizes from the prototypes of today to large-scale computers3–5. Recent advances in silicon-based qubits have enabled the implementations of high-quality one-qubit and two-qubit systems6–8. However, the demonstration of QEC, which requires three or more coupled qubits1, and involves a three-qubit gate9–11 or measurement-based feedback, remains an open challenge. Here we demonstrate a three-qubit phase-correcting code in silicon, in which an encoded three-qubit state is protected against any phase-flip error on one of the three qubits. The correction to this encoded state is performed by a three-qubit conditional rotation, which we implement by an efficient single-step resonantly driven iToffoli gate. As expected, the error correction mitigates the errors owing to one-qubit phase-flip, as well as the intrinsic dephasing mainly owing to quasi-static phase noise. These results show successful implementation of QEC and the potential of a silicon-based platform for large-scale quantum computing.
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Tahan, Charles. "Opinion: Democratizing Spin Qubits." Quantum 5 (November 18, 2021): 584. http://dx.doi.org/10.22331/q-2021-11-18-584.
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I've been building Powerpoint-based quantum computers with electron spins in silicon for 20 years. Unfortunately, real-life-based quantum dot quantum computers are harder to implement. Materials, fabrication, and control challenges still impede progress. The way to accelerate discovery is to make and measure more qubits. Here I discuss separating the qubit realization and testing circuitry from the materials science and on-chip fabrication that will ultimately be necessary. This approach should allow us, in the shorter term, to characterize wafers non-invasively for their qubit-relevant properties, to make small qubit systems on various different materials with little extra cost, and even to test spin-qubit to superconducting cavity entanglement protocols where the best possible cavity quality is preserved. Such a testbed can advance the materials science of semiconductor quantum information devices and enable small quantum computers. This article may also be useful as a light and light-hearted introduction to quantum dot spin qubits.
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Aldeghi, Michele, Rolf Allenspach, and Gian Salis. "Modular nanomagnet design for spin qubits confined in a linear chain." Applied Physics Letters 122, no. 13 (March 27, 2023): 134003. http://dx.doi.org/10.1063/5.0139670.
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On-chip micromagnets enable electrically controlled quantum gates on electron spin qubits. Extending the concept to a large number of qubits is challenging in terms of providing large enough driving gradients and individual addressability. Here, we present a design aimed at driving spin qubits arranged in a linear chain and strongly confined in directions lateral to the chain. Nanomagnets are placed laterally to the one side of the qubit chain, one nanomagnet per two qubits. The individual magnets are “U”-shaped, such that the magnetic shape anisotropy orients the magnetization alternately toward and against the qubit chain even if an external magnetic field is applied along the qubit chain. The longitudinal and transversal stray field components serve as addressability and driving fields. Using micromagnetic simulations, we calculate driving and dephasing rates and the corresponding qubit quality factor. The concept is validated with spin-polarized scanning electron microscopy of Fe nanomagnets fabricated on silicon substrates, finding excellent agreement with micromagnetic simulations. Several features required for a scalable spin qubit design are met in our approach: strong driving and weak dephasing gradients, reduced crosstalk and operation at low external magnetic fields.
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Vlasov, Alexander Yu. "Quantum circuits and Spin(3n) groups." Quantum Information and Computation 15, no. 3&4 (March 2015): 235–59. http://dx.doi.org/10.26421/qic15.3-4-3.
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All quantum gates with one and two qubits may be described by elements of Spin groups due to isomorphisms Spin(3)\isomSU(2) and Spin(6)\isomSU(4). However, the group of n-qubit gates SU(2^n) for n>2 has bigger dimension than Spin(3n). A quantum circuit with one- and two-qubit gates may be used for construction of arbitrary unitary transformation SU(2^n). Analogously, the `$Spin(3n)$ circuits' are introduced in this work as products of elements associated with one- and two-qubit gates with respect to the above-mentioned isomorphisms. The matrix tensor product implementation of the Spin(3n) group together with relevant models by usual quantum circuits with 2n qubits are investigated in such a framework. A certain resemblance with well-known sets of non-universal quantum gates (e.g., matchgates, noninteracting-fermion quantum circuits) related with Spin(2n) may be found in presented approach. Finally, a possibility of the classical simulation of such circuits in polynomial time is discussed.
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Wang, Yu, Yi Chen, Hong T. Bui, Christoph Wolf, Masahiro Haze, Cristina Mier, Jinkyung Kim, et al. "An atomic-scale multi-qubit platform." Science 382, no. 6666 (October 6, 2023): 87–92. http://dx.doi.org/10.1126/science.ade5050.
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Individual electron spins in solids are promising candidates for quantum science and technology, where bottom-up assembly of a quantum device with atomically precise couplings has long been envisioned. Here, we realized atom-by-atom construction, coherent operations, and readout of coupled electron-spin qubits using a scanning tunneling microscope. To enable the coherent control of “remote” qubits that are outside of the tunnel junction, we complemented each electron spin with a local magnetic field gradient from a nearby single-atom magnet. Readout was achieved by using a sensor qubit in the tunnel junction and implementing pulsed double electron spin resonance. Fast single-, two-, and three-qubit operations were thereby demonstrated in an all-electrical fashion. Our angstrom-scale qubit platform may enable quantum functionalities using electron spin arrays built atom by atom on a surface.
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Xue, Xiao, Maximilian Russ, Nodar Samkharadze, Brennan Undseth, Amir Sammak, Giordano Scappucci, and Lieven M. K. Vandersypen. "Quantum logic with spin qubits crossing the surface code threshold." Nature 601, no. 7893 (January 19, 2022): 343–47. http://dx.doi.org/10.1038/s41586-021-04273-w.
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AbstractHigh-fidelity control of quantum bits is paramount for the reliable execution of quantum algorithms and for achieving fault tolerance—the ability to correct errors faster than they occur1. The central requirement for fault tolerance is expressed in terms of an error threshold. Whereas the actual threshold depends on many details, a common target is the approximately 1% error threshold of the well-known surface code2,3. Reaching two-qubit gate fidelities above 99% has been a long-standing major goal for semiconductor spin qubits. These qubits are promising for scaling, as they can leverage advanced semiconductor technology4. Here we report a spin-based quantum processor in silicon with single-qubit and two-qubit gate fidelities, all of which are above 99.5%, extracted from gate-set tomography. The average single-qubit gate fidelities remain above 99% when including crosstalk and idling errors on the neighbouring qubit. Using this high-fidelity gate set, we execute the demanding task of calculating molecular ground-state energies using a variational quantum eigensolver algorithm5. Having surpassed the 99% barrier for the two-qubit gate fidelity, semiconductor qubits are well positioned on the path to fault tolerance and to possible applications in the era of noisy intermediate-scale quantum devices.
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Hu, Rui-Zi, Rong-Long Ma, Ming Ni, Yuan Zhou, Ning Chu, Wei-Zhu Liao, Zhen-Zhen Kong, et al. "Flopping-mode spin qubit in a Si-MOS quantum dot." Applied Physics Letters 122, no. 13 (March 27, 2023): 134002. http://dx.doi.org/10.1063/5.0137259.
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Spin qubits based on silicon metal-oxide semiconductor (Si-MOS) quantum dots (QDs) are promising platforms for large-scale quantum computers. To control spin qubits in QDs, electric dipole spin resonance (EDSR) has been most commonly used in recent years. By delocalizing an electron across a double quantum dots charge state, “flopping-mode” EDSR has been realized in Si/SiGe QDs. Here, we demonstrate a flopping-mode spin qubit in a Si-MOS QD via Elzerman single-shot readout. When changing the detuning with a fixed drive power, we achieve s-shape spin resonance frequencies, an order of magnitude improvement in the spin Rabi frequencies, and virtually constant spin dephasing times. Our results offer a route to large-scale spin qubit systems with higher control fidelity in Si-MOS QDs.
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Koh, C. Y. "Entanglement and quantum spin glass." International Journal of Modern Physics B 28, no. 20 (June 19, 2014): 1430012. http://dx.doi.org/10.1142/s0217979214300126.
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The paper reviews the entanglement behavior of a 2-qubit system in a quantum spin glass using the Heisenberg XX model and the interaction of the system with a spin glass bath environment. In the first part, we study the entanglement (concurrence) for a 3- and 4-qubit with nearest neighbor interaction. With a fixed mean and varying standard deviation for the J coupling, the concurrence is numerically plotted with temperature for the different configurations. A general formula for the concurrence is given for n qubits at low temperature. In the second part, we study the concurrence of a 2-qubit system coupled to a spin glass bath environment with n = 2 to ≥ 4 qubits. The bath sites are coupled with random J coupling and varying applied magnetic field. A general formula for concurrence is given for mean J = 0 and B = 0 for n bath sites. For small random J and magnetic field B, a steady state is obtained with an approximate concurrence of 0.5, showing that the entanglement is preserved.
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King, Andrew D., Cristiano Nisoli, Edward D. Dahl, Gabriel Poulin-Lamarre, and Alejandro Lopez-Bezanilla. "Qubit spin ice." Science 373, no. 6554 (July 15, 2021): 576–80. http://dx.doi.org/10.1126/science.abe2824.
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Artificial spin ices are frustrated spin systems that can be engineered, in which fine tuning of geometry and topology has allowed the design and characterization of exotic emergent phenomena at the constituent level. Here, we report a realization of spin ice in a lattice of superconducting qubits. Unlike conventional artificial spin ice, our system is disordered by both quantum and thermal fluctuations. The ground state is classically described by the ice rule, and we achieved control over a fragile degeneracy point, leading to a Coulomb phase. The ability to pin individual spins allows us to demonstrate Gauss’s law for emergent effective monopoles in two dimensions. The demonstrated qubit control lays the groundwork for potential future study of topologically protected artificial quantum spin liquids.
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Huang, Jonathan Y., Rocky Y. Su, Wee Han Lim, MengKe Feng, Barnaby van Straaten, Brandon Severin, Will Gilbert, et al. "High-fidelity spin qubit operation and algorithmic initialization above 1 K." Nature 627, no. 8005 (March 27, 2024): 772–77. http://dx.doi.org/10.1038/s41586-024-07160-2.
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AbstractThe encoding of qubits in semiconductor spin carriers has been recognized as a promising approach to a commercial quantum computer that can be lithographically produced and integrated at scale1–10. However, the operation of the large number of qubits required for advantageous quantum applications11–13 will produce a thermal load exceeding the available cooling power of cryostats at millikelvin temperatures. As the scale-up accelerates, it becomes imperative to establish fault-tolerant operation above 1 K, at which the cooling power is orders of magnitude higher14–18. Here we tune up and operate spin qubits in silicon above 1 K, with fidelities in the range required for fault-tolerant operations at these temperatures19–21. We design an algorithmic initialization protocol to prepare a pure two-qubit state even when the thermal energy is substantially above the qubit energies and incorporate radiofrequency readout to achieve fidelities up to 99.34% for both readout and initialization. We also demonstrate single-qubit Clifford gate fidelities up to 99.85% and a two-qubit gate fidelity of 98.92%. These advances overcome the fundamental limitation that the thermal energy must be well below the qubit energies for the high-fidelity operation to be possible, surmounting a main obstacle in the pathway to scalable and fault-tolerant quantum computation.
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Neyens, Samuel, Otto K. Zietz, Thomas F. Watson, Florian Luthi, Aditi Nethwewala, Hubert C. George, Eric Henry, et al. "Probing single electrons across 300-mm spin qubit wafers." Nature 629, no. 8010 (May 1, 2024): 80–85. http://dx.doi.org/10.1038/s41586-024-07275-6.
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AbstractBuilding a fault-tolerant quantum computer will require vast numbers of physical qubits. For qubit technologies based on solid-state electronic devices1–3, integrating millions of qubits in a single processor will require device fabrication to reach a scale comparable to that of the modern complementary metal–oxide–semiconductor (CMOS) industry. Equally important, the scale of cryogenic device testing must keep pace to enable efficient device screening and to improve statistical metrics such as qubit yield and voltage variation. Spin qubits1,4,5 based on electrons in Si have shown impressive control fidelities6–9 but have historically been challenged by yield and process variation10–12. Here we present a testing process using a cryogenic 300-mm wafer prober13 to collect high-volume data on the performance of hundreds of industry-manufactured spin qubit devices at 1.6 K. This testing method provides fast feedback to enable optimization of the CMOS-compatible fabrication process, leading to high yield and low process variation. Using this system, we automate measurements of the operating point of spin qubits and investigate the transitions of single electrons across full wafers. We analyse the random variation in single-electron operating voltages and find that the optimized fabrication process leads to low levels of disorder at the 300-mm scale. Together, these results demonstrate the advances that can be achieved through the application of CMOS-industry techniques to the fabrication and measurement of spin qubit devices.
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Yamamoto, Satoru, Shigeaki Nakazawa, Kenji Sugisaki, Kazunobu Sato, Kazuo Toyota, Daisuke Shiomi, and Takeji Takui. "Adiabatic quantum computing with spin qubits hosted by molecules." Physical Chemistry Chemical Physics 17, no. 4 (2015): 2742–49. http://dx.doi.org/10.1039/c4cp04744c.
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GÜN, A., I. ŞAKA, and A. GENÇTEN. "CONSTRUCTION AND APPLICATION OF FOUR-QUBIT SWAP LOGIC GATE IN NMR QUANTUM COMPUTING." International Journal of Quantum Information 09, no. 02 (March 2011): 779–90. http://dx.doi.org/10.1142/s0219749911007721.
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In NMR quantum computing, spin states of spin-1/2 nuclei are called qubits. Quantum logic gates are represented by unitary matrices. As a universal gate, controlled-NOT (CNOT) is a two-qubit gate. For the IS (I = 1/2 and S = 1/2) spin system, two-qubit CNOT gate is represented by a 4 × 4 matrix. SWAP logic gate, which exchanges two quantum states, is constructed by CNOT gates. In this study, first, four-qubit CNOT gates are constructed for the IS (I = 3/2, S = 3/2) spin system. Then, by using these CNOT gates, a four-qubit SWAP logic gate is found. As an application and verification, an obtained SWAP logic gate is applied to the matrix representation of product operators for the IS (I = 3/2, S = 3/2) spin system. SWAP logic gate can also be presented by an NMR pulse sequence. By using the product operator theory, the pulse sequence of the SWAP logic gate is applied to product operators of the IS (I = 3/2, S = 3/2) spin system. The expected exchange results are obtained for both the matrix representation and the pulse sequence of SWAP logic gate.
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Vahapoglu, Ensar, James P. Slack-Smith, Ross C. C. Leon, Wee Han Lim, Fay E. Hudson, Tom Day, Tuomo Tanttu, et al. "Single-electron spin resonance in a nanoelectronic device using a global field." Science Advances 7, no. 33 (August 2021): eabg9158. http://dx.doi.org/10.1126/sciadv.abg9158.
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Spin-based silicon quantum electronic circuits offer a scalable platform for quantum computation, combining the manufacturability of semiconductor devices with the long coherence times afforded by spins in silicon. Advancing from current few-qubit devices to silicon quantum processors with upward of a million qubits, as required for fault-tolerant operation, presents several unique challenges, one of the most demanding being the ability to deliver microwave signals for large-scale qubit control. Here, we demonstrate a potential solution to this problem by using a three-dimensional dielectric resonator to broadcast a global microwave signal across a quantum nanoelectronic circuit. Critically, this technique uses only a single microwave source and is capable of delivering control signals to millions of qubits simultaneously. We show that the global field can be used to perform spin resonance of single electrons confined in a silicon double quantum dot device, establishing the feasibility of this approach for scalable spin qubit control.
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Cuccoli, Alessandro, Davide Nuzzi, Ruggero Vaia, and Paola Verrucchi. "Using solitons for manipulating qubits." International Journal of Quantum Information 12, no. 02 (March 2014): 1461013. http://dx.doi.org/10.1142/s0219749914610139.
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Many proposals for quantum devices are based on qubits that are physically realized by the spin magnetic moment of some quantum object. In this case, one of the most often adopted strategies for manipulating qubits is that of using external magnetic fields. However, selectively applying a field just to one qubit may be a practically unattainable goal, as it is, for instance, in most solid-state based setups. In this work, we present a proposal for using nonlinear excitations of solitonic type to accomplish the above task. Our scheme entails the generation of a dynamical soliton in a classical spin-chain which is locally coupled with one qubit: as the soliton runs through, the qubit behaves, due to its interaction with the chain, as if it were subject to a magnetic field with a time dependence that follows from the soliton's features. We here present results for the time evolution of the qubit density-matrix induced by the overall dynamics of the above scheme.
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Tanuma, Yuri, Anastasios Stergiou, Andreja Bužan Bobnar, Mattia Gaboardi, Jeremy Rio, Jannis Volkmann, Hermann A. Wegner, Nikos Tagmatarchis, Christopher P. Ewels, and Denis Arčon. "Robust coherent spin centers from stable azafullerene radicals entrapped in cycloparaphenylene rings." Nanoscale 13, no. 47 (2021): 19946–55. http://dx.doi.org/10.1039/d1nr06393f.
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Stable and abundant spin-1/2 species from azafullerene (C59N˙) supramolecularly hosted in [10]cycloparaphenylene nanohoops are operated as stable qubits, with possibility of qubit wiring via intermediate polymerized spin-redistributed states.
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Horiuchi, Noriaki. "Flying qubit carrying a spin qubit." Nature Photonics 7, no. 4 (March 27, 2013): 336. http://dx.doi.org/10.1038/nphoton.2013.78.
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APPN Editorial Office. "Highlights from the Asia Pacific Region." Asia Pacific Physics Newsletter 02, no. 02 (August 2013): 29–46. http://dx.doi.org/10.1142/s2251158x13000271.
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Quantum information technologies hold the promise of greatly outperforming traditional approaches in, e.g., cryptography, metrology and simulation. However, the ultimate goal of realizing scalable quantum computing has so far remained elusive, largely owing to the formidable difficulty in "wiring up" suitable quantum bits (qubits). In recent years, individual nitrogen-vacancy (NV-) defects in diamond have emerged as one of the most promising candidates for a solidstate qubit for two reasons. First, they possess the longest observed room-temperature coherence time of an electron spin (the qubit) to date; second, their spin can be initialized and measured with a nanoscale resolution using optical techniques under ambient conditions. However, interconnecting different NV- centres remains a big challenge. This problem is further exacerbated by the need for a large spatial separation between adjacent qubits, required for individual qubit addressability.
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BERMAN, G. P., A. R. BISHOP, F. BORGONOVI, and V. I. TSIFRINOVICH. "CONTROLLABLE ADIABATIC MANIPULATION OF THE QUBIT STATE." International Journal of Quantum Information 05, no. 05 (October 2007): 667–72. http://dx.doi.org/10.1142/s0219749907003110.
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We propose a scheme which implements a controllable change of the state of the target spin qubit in such a way that both the control and the target spin qubits remain in their ground states. The interaction between the two spins is mediated by an auxiliary spin, which can transfer to its excited state. Our scheme suggests a possible relationship between the gate and adiabatic quantum computation.
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Hays, M., V. Fatemi, D. Bouman, J. Cerrillo, S. Diamond, K. Serniak, T. Connolly, et al. "Coherent manipulation of an Andreev spin qubit." Science 373, no. 6553 (July 22, 2021): 430–33. http://dx.doi.org/10.1126/science.abf0345.
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Two promising architectures for solid-state quantum information processing are based on electron spins electrostatically confined in semiconductor quantum dots and the collective electrodynamic modes of superconducting circuits. Superconducting electrodynamic qubits involve macroscopic numbers of electrons and offer the advantage of larger coupling, whereas semiconductor spin qubits involve individual electrons trapped in microscopic volumes but are more difficult to link. We combined beneficial aspects of both platforms in the Andreev spin qubit: the spin degree of freedom of an electronic quasiparticle trapped in the supercurrent-carrying Andreev levels of a Josephson semiconductor nanowire. We performed coherent spin manipulation by combining single-shot circuit–quantum-electrodynamics readout and spin-flipping Raman transitions and found a spin-flip time TS = 17 microseconds and a spin coherence time T2E = 52 nanoseconds. These results herald a regime of supercurrent-mediated coherent spin-photon coupling at the single-quantum level.
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Osborne, Ian S. "Superconducting spin qubit." Science 373, no. 6553 (July 22, 2021): 405.14–407. http://dx.doi.org/10.1126/science.373.6553.405-n.
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Royer, Baptiste, Arne L. Grimsmo, Nicolas Didier, and Alexandre Blais. "Fast and high-fidelity entangling gate through parametrically modulated longitudinal coupling." Quantum 1 (May 11, 2017): 11. http://dx.doi.org/10.22331/q-2017-05-11-11.
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We investigate an approach to universal quantum computation based on the modulation of longitudinal qubit-oscillator coupling. We show how to realize a controlled-phase gate by simultaneously modulating the longitudinal coupling of two qubits to a common oscillator mode. In contrast to the more familiar transversal qubit-oscillator coupling, the magnitude of the effective qubit-qubit interaction does not rely on a small perturbative parameter. As a result, this effective interaction strength can be made large, leading to short gate times and high gate fidelities. We moreover show how the gate infidelity can be exponentially suppressed with squeezing and how the entangling gate can be generalized to qubits coupled to separate oscillators. Our proposal can be realized in multiple physical platforms for quantum computing, including superconducting and spin qubits.
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METWALLY, N., M. ABDEL-ATY, and A. S. OBADA. "COHERENT AND INCOHERENT BEHAVIORS OF QUBITS INTERACTING WITH A SPIN-PATH PARTICLE." International Journal of Modern Physics B 27, no. 17 (July 3, 2013): 1350076. http://dx.doi.org/10.1142/s0217979213500768.
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We analyze a crucial effect of the spin-path environment on a single and maximum entangled two-qubit systems. For a single qubit, we investigate the coherent loss by means of coherent-vectors' dynamics and the interacted qubits' fidelity. We used entanglement and population dynamics to investigate the coherent loss of the two-qubit system. We show and numerically verify that the effect of the detuning and coupling parameters in the negativity can be mapped onto the maximum and minimum values of the entanglement.
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Borgarino, Mattia. "Circuit-Based Compact Model of Electron Spin Qubit." Electronics 11, no. 4 (February 10, 2022): 526. http://dx.doi.org/10.3390/electronics11040526.
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Today, an electron spin qubit on silicon appears to be a very promising physical platform for the fabrication of future quantum microprocessors. Thousands of these qubits should be packed together into one single silicon die in order to break the quantum supremacy barrier. Microelectronics engineers are currently leveraging on the current CMOS technology to design the manipulation and read-out electronics as cryogenic integrated circuits. Several of these circuits are RFICs, as VCO, LNA, and mixers. Therefore, the availability of a qubit CAD model plays a central role in the proper design of these cryogenic RFICs. The present paper reports on a circuit-based compact model of an electron spin qubit for CAD applications. The proposed model is described and tested, and the limitations faced are highlighted and discussed.
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Lino, Jéssica Boreli dos Reis, Mateus Aquino Gonçalves, Stephan P. A. Sauer, and Teodorico Castro Ramalho. "Extending NMR Quantum Computation Systems by Employing Compounds with Several Heavy Metals as Qubits." Magnetochemistry 8, no. 5 (April 21, 2022): 47. http://dx.doi.org/10.3390/magnetochemistry8050047.
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Nuclear magnetic resonance (NMR) is a spectroscopic method that can be applied to several areas. Currently, this technique is also being used as an experimental quantum simulator, where nuclear spins are employed as quantum bits or qubits. The present work is devoted to studying heavy metal complexes as possible candidates to act as qubit molecules. Nuclei such 113Cd, 199Hg, 125Te, and 77Se assembled with the most common employed nuclei in NMR-QIP implementations (1H, 13C, 19F, 29Si, and 31P) could potentially be used in heteronuclear systems for NMR-QIP implementations. Hence, aiming to contribute to the development of future scalable heteronuclear spin systems, we specially designed four complexes, based on the auspicious qubit systems proposed in our previous work, which will be explored by quantum chemical calculations of their NMR parameters and proposed as suitable qubit molecules. Chemical shifts and spin–spin coupling constants in four complexes were examined using the spin–orbit zeroth-order regular approximation (ZORA) at the density functional theory (DFT) level, as well as the relaxation parameters (T1 and T2). Examining the required spectral properties of NMR-QIP, all the designed complexes were found to be promising candidates for qubit molecules.
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Cai, Zhenyu, Michael A. Fogarty, Simon Schaal, Sofia Patomäki, Simon C. Benjamin, and John J. L. Morton. "A Silicon Surface Code Architecture Resilient Against Leakage Errors." Quantum 3 (December 9, 2019): 212. http://dx.doi.org/10.22331/q-2019-12-09-212.
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Spin qubits in silicon quantum dots are one of the most promising building blocks for large scale quantum computers thanks to their high qubit density and compatibility with the existing semiconductor technologies. High fidelity single-qubit gates exceeding the threshold of error correction codes like the surface code have been demonstrated, while two-qubit gates have reached 98% fidelity and are improving rapidly. However, there are other types of error --- such as charge leakage and propagation --- that may occur in quantum dot arrays and which cannot be corrected by quantum error correction codes, making them potentially damaging even when their probability is small. We propose a surface code architecture for silicon quantum dot spin qubits that is robust against leakage errors by incorporating multi-electron mediator dots. Charge leakage in the qubit dots is transferred to the mediator dots via charge relaxation processes and then removed using charge reservoirs attached to the mediators. A stabiliser-check cycle, optimised for our hardware, then removes the correlations between the residual physical errors. Through simulations we obtain the surface code threshold for the charge leakage errors and show that in our architecture the damage due to charge leakage errors is reduced to a similar level to that of the usual depolarising gate noise. Spin leakage errors in our architecture are constrained to only ancilla qubits and can be removed during quantum error correction via reinitialisations of ancillae, which ensure the robustness of our architecture against spin leakage as well. Our use of an elongated mediator dots creates spaces throughout the quantum dot array for charge reservoirs, measuring devices and control gates, providing the scalability in the design.
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Chernega, Vladimir N., Margarita A. Man’ko, and Vladimir I. Man’ko. "PT -Symmetric Qubit-System States in the Probability Representation of Quantum Mechanics." Symmetry 12, no. 10 (October 16, 2020): 1702. http://dx.doi.org/10.3390/sym12101702.
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PT-symmetric qubit-system states are considered in the probability representation of quantum mechanics. The new energy eigenvalue equation for probability distributions identified with qubit and qutrit states is presented in an explicit form. A possibility to test PT-symmetry and its violation by measuring the probabilities of spin projections for qubits in three perpendicular directions is discussed.
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Hill, Charles D., Eldad Peretz, Samuel J. Hile, Matthew G. House, Martin Fuechsle, Sven Rogge, Michelle Y. Simmons, and Lloyd C. L. Hollenberg. "A surface code quantum computer in silicon." Science Advances 1, no. 9 (October 2015): e1500707. http://dx.doi.org/10.1126/sciadv.1500707.
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The exceptionally long quantum coherence times of phosphorus donor nuclear spin qubits in silicon, coupled with the proven scalability of silicon-based nano-electronics, make them attractive candidates for large-scale quantum computing. However, the high threshold of topological quantum error correction can only be captured in a two-dimensional array of qubits operating synchronously and in parallel—posing formidable fabrication and control challenges. We present an architecture that addresses these problems through a novel shared-control paradigm that is particularly suited to the natural uniformity of the phosphorus donor nuclear spin qubit states and electronic confinement. The architecture comprises a two-dimensional lattice of donor qubits sandwiched between two vertically separated control layers forming a mutually perpendicular crisscross gate array. Shared-control lines facilitate loading/unloading of single electrons to specific donors, thereby activating multiple qubits in parallel across the array on which the required operations for surface code quantum error correction are carried out by global spin control. The complexities of independent qubit control, wave function engineering, and ad hoc quantum interconnects are explicitly avoided. With many of the basic elements of fabrication and control based on demonstrated techniques and with simulated quantum operation below the surface code error threshold, the architecture represents a new pathway for large-scale quantum information processing in silicon and potentially in other qubit systems where uniformity can be exploited.
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Takeda, Kenta, Jun Kamioka, Tomohiro Otsuka, Jun Yoneda, Takashi Nakajima, Matthieu R. Delbecq, Shinichi Amaha, et al. "A fault-tolerant addressable spin qubit in a natural silicon quantum dot." Science Advances 2, no. 8 (August 2016): e1600694. http://dx.doi.org/10.1126/sciadv.1600694.
Full textAbstract:
Fault-tolerant quantum computing requires high-fidelity qubits. This has been achieved in various solid-state systems, including isotopically purified silicon, but is yet to be accomplished in industry-standard natural (unpurified) silicon, mainly as a result of the dephasing caused by residual nuclear spins. This high fidelity can be achieved by speeding up the qubit operation and/or prolonging the dephasing time, that is, increasing the Rabi oscillation quality factor Q (the Rabi oscillation decay time divided by the π rotation time). In isotopically purified silicon quantum dots, only the second approach has been used, leaving the qubit operation slow. We apply the first approach to demonstrate an addressable fault-tolerant qubit using a natural silicon double quantum dot with a micromagnet that is optimally designed for fast spin control. This optimized design allows access to Rabi frequencies up to 35 MHz, which is two orders of magnitude greater than that achieved in previous studies. We find the optimum Q = 140 in such high-frequency range at a Rabi frequency of 10 MHz. This leads to a qubit fidelity of 99.6% measured via randomized benchmarking, which is the highest reported for natural silicon qubits and comparable to that obtained in isotopically purified silicon quantum dot–based qubits. This result can inspire contributions to quantum computing from industrial communities.
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Boerkamp, Martijn. "Six-qubit silicon quantum processor sets a record." Physics World 35, no. 12 (December 1, 2022): 6i. http://dx.doi.org/10.1088/2058-7058/35/12/06.
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GÜN, A., and A. GENÇTEN. "THREE-QUBIT QUANTUM ENTANGLEMENT FOR SI (S = 3/2, I = 1/2) SPIN SYSTEM." International Journal of Quantum Information 09, no. 07n08 (October 2011): 1635–42. http://dx.doi.org/10.1142/s0219749911008313.
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In quantum information processing, spin-3/2 electron or nuclear spin states are known as two-qubit states. For SI (S = 3/2, I = 1/2) spin system, there are eight three-qubit states. In this study, first, three-qubit CNOT logic gates are obtained. Then three-qubit entangled states are obtained by using the matrix representation of Hadamard and three-qubit CNOT logic gates. By considering single 31P@C60 molecule as SI (S = 3/2, I = 1/2) spin system, three-qubit entangled states are also obtained using the magnetic resonance pulse sequences of Hadamard and CNOT logic gates.
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Moreno-Pineda, Eufemio, Clément Godfrin, Franck Balestro, Wolfgang Wernsdorfer, and Mario Ruben. "Molecular spin qudits for quantum algorithms." Chemical Society Reviews 47, no. 2 (2018): 501–13. http://dx.doi.org/10.1039/c5cs00933b.
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Molecules are promising building blocks for Quantum information processing. Herein we describe how a molecular multilevel nuclear spin qubit (or qudit, where d = 4), known as TbPc2, showing all necessary requirements to perform as a molecular hardware platform with a first generation of molecular devices enabling even quantum algorithm operations.
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Benenti, G., G. Casati, and S. Montangero. "Stability of Quantum Computing in the Presence of Imperfections." International Journal of Modern Physics B 17, no. 22n24 (September 30, 2003): 3932–46. http://dx.doi.org/10.1142/s0217979203021927.
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We model an isolated quantum computer as a two-dimensional lattice of qubits (spin halves) with fluctuations in individual qubit energies and residual short-range inter-qubit couplings. We show that above a critical inter-qubit coupling strength, quantum chaos sets in and this results in the interaction induced dynamical thermalization and occupation numbers well described by the Fermi–Dirac distribution. This thermalization destroys the noninteracting qubit structure and sets serious requirements for the quantum computer operability. We then construct a quantum algorithm which uses qubits in an optimal way and efficiently simulates a physical model with rich and complex dynamics. The numerical study of the effect of static imperfections in the quantum computer hardware shows that the main elements of the phase space structures are accurately reproduced up to a time scale which is polynomial in the number of qubits. The errors generated by these imperfections are more significant than the errors of random noise in gate operations.
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Noiri, Akito, Kenta Takeda, Takashi Nakajima, Takashi Kobayashi, Amir Sammak, Giordano Scappucci, and Seigo Tarucha. "A shuttling-based two-qubit logic gate for linking distant silicon quantum processors." Nature Communications 13, no. 1 (September 30, 2022). http://dx.doi.org/10.1038/s41467-022-33453-z.
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AbstractControl of entanglement between qubits at distant quantum processors using a two-qubit gate is an essential function of a scalable, modular implementation of quantum computation. Among the many qubit platforms, spin qubits in silicon quantum dots are promising for large-scale integration along with their nanofabrication capability. However, linking distant silicon quantum processors is challenging as two-qubit gates in spin qubits typically utilize short-range exchange coupling, which is only effective between nearest-neighbor quantum dots. Here we demonstrate a two-qubit gate between spin qubits via coherent spin shuttling, a key technology for linking distant silicon quantum processors. Coherent shuttling of a spin qubit enables efficient switching of the exchange coupling with an on/off ratio exceeding 1000, while preserving the spin coherence by 99.6% for the single shuttling between neighboring dots. With this shuttling-mode exchange control, we demonstrate a two-qubit controlled-phase gate with a fidelity of 93%, assessed via randomized benchmarking. Combination of our technique and a phase coherent shuttling of a qubit across a large quantum dot array will provide feasible path toward a quantum link between distant silicon quantum processors, a key requirement for large-scale quantum computation.
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Landig, A. J., J. V. Koski, P. Scarlino, C. Müller, J. C. Abadillo-Uriel, B. Kratochwil, C. Reichl, et al. "Virtual-photon-mediated spin-qubit–transmon coupling." Nature Communications 10, no. 1 (November 6, 2019). http://dx.doi.org/10.1038/s41467-019-13000-z.
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Abstract Spin qubits and superconducting qubits are among the promising candidates for realizing a solid state quantum computer. For the implementation of a hybrid architecture which can profit from the advantages of either approach, a coherent link is necessary that integrates and controllably couples both qubit types on the same chip over a distance that is several orders of magnitude longer than the physical size of the spin qubit. We realize such a link with a frequency-tunable high impedance SQUID array resonator. The spin qubit is a resonant exchange qubit hosted in a GaAs triple quantum dot. It can be operated at zero magnetic field, allowing it to coexist with superconducting qubits on the same chip. We spectroscopically observe coherent interaction between the resonant exchange qubit and a transmon qubit in both resonant and dispersive regimes, where the interaction is mediated either by real or virtual resonator photons.
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Srinivasa, V., J. M. Taylor, and J. R. Petta. "Cavity-Mediated Entanglement of Parametrically Driven Spin Qubits via Sidebands." PRX Quantum 5, no. 2 (May 21, 2024). http://dx.doi.org/10.1103/prxquantum.5.020339.
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We consider a pair of quantum dot-based spin qubits that interact via microwave photons in a superconducting cavity and that are also parametrically driven by separate external electric fields. For this system, we formulate a model for spin qubit entanglement in the presence of mutually off-resonant qubit and cavity frequencies. We show that the sidebands generated via the driving fields enable highly tunable qubit-qubit entanglement using only ac control and without requiring the qubit and cavity frequencies to be tuned into simultaneous resonance. The model we derive can be mapped to a variety of qubit types, including detuning-driven one-electron spin qubits in double quantum dots and three-electron resonant exchange qubits in triple quantum dots. The high degree of nonlinearity inherent in spin qubits renders these systems particularly favorable for parametric drive-activated entanglement. We determine multiple common resonance conditions for the two driven qubits and the cavity and identify experimentally relevant parameter regimes that enable the implementation of entangling gates with suppressed sensitivity to cavity photon occupation and decay. The parametrically driven sideband resonance approach that we describe provides a promising route toward scalability and modularity in spin-based quantum information processing through drive-enabled tunability that can also be implemented in micromagnet-free electron and hole systems for spin-photon coupling. Published by the American Physical Society 2024
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Wang Ning, Wang Bao-Chuan, and Guo Guo-Ping. "New progress in silicon-based semiconductor quantum computation." Acta Physica Sinica, 2022, 0. http://dx.doi.org/10.7498/aps.71.20221900.
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Spin qubits in silicon-based semiconductor quantum dots have become one of the prominent candidates for realizing fault-tolerant quantum computing due to their long coherence time, good controllability, and compatibility with modern advanced integrated circuit manufacturing processes. In recent years, thanks to the remarkable progress made in silicon-based materials, structure of quantum dot and its fabrication process, and qubit manipulation technology, high-fidelity state preparation and readout, single- and two-qubit gates have been demonstrated for silicon spin qubits. The control fidelities for single- and two-qubit gates all exceed 99%—fault tolerance threshold required by the surface code known for its exceptionally high tolerance to errors. In this paper, we briefly introduce the basic concepts of silicon-based semiconductor quantum dots, discuss the state-of-art technologies used to improve the fidelities of single- and two-qubit gates, and finally highlight the research directions that need to be focused on.<br />The paper is organized as follows. Firstly, we introduce three major types of quantum dots (QD) devices fabricated on different silicon-based substrate, including Si/SiGe heterojunction and Si/SiO<sub>2</sub>. The spin degree of electron or nuclear hosted in QD can be encoded to spin qubits. Electron spin qubit can be thermal initialized to ground state utilizing electron reservoirs and read out by spin-charge conversion mechanism energy-selective readout (Elzerman readout) with reservoirs or Pauli spin blockade (PSB) needless for a reservoir. Additionally, high fidelity single-shot readout has been demonstrated using radio-frequency gate reflectometry combined with PSB, which has unique advantages in large-scale qubit array. To coherent control the spin qubits, electron dipole renounce (ESR) or electron dipole spin resonance (EDSR) for electron and nuclear magnetic resonance (NMR) for nuclear are introduced. With help of isotope purification greatly improving the dephasing time of qubit and fast single-qubit manipulation based on EDSR, fidelity above 99.9 percent can be reached. For the two-qubit gates based on exchange interaction between electron spins, the strength of interaction <em>J</em> combined with Zeeman energy difference Δ<em>E</em><sub><em>Z</em></sub> determines the energy levels of system, which lead to the different two-qubit gates, such as controlled-Z (CZ), controlled-Rotation (CROT) and the square root of the SWAP gate ($\sqrt{\text { SWAP }}$) gates. In order to improve the fidelity of two-qubit gates, a series of key technologies are used in the experiments, not only isotope purification but also symmetry operation, careful Hamiltonian engineering and gate set tomography. Fidelity of two-qubit gates exceeding 99 percent has been demonstrated for electron spin qubits in Si/SiGe quantum dots and nuclear spin qubits in donors. These progresses have pushed the silicon-based spin qubits platform to constitute a major stepping stone towards fault-tolerant quantum computation. Finally, we discuss the next step for spin qubits, that is, how to effectively expand the number of qubits and there are still many problems to be explored and solved.
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Yoneda, J., W. Huang, M. Feng, C. H. Yang, K. W. Chan, T. Tanttu, W. Gilbert, et al. "Coherent spin qubit transport in silicon." Nature Communications 12, no. 1 (July 5, 2021). http://dx.doi.org/10.1038/s41467-021-24371-7.
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AbstractA fault-tolerant quantum processor may be configured using stationary qubits interacting only with their nearest neighbours, but at the cost of significant overheads in physical qubits per logical qubit. Such overheads could be reduced by coherently transporting qubits across the chip, allowing connectivity beyond immediate neighbours. Here we demonstrate high-fidelity coherent transport of an electron spin qubit between quantum dots in isotopically-enriched silicon. We observe qubit precession in the inter-site tunnelling regime and assess the impact of qubit transport using Ramsey interferometry and quantum state tomography techniques. We report a polarization transfer fidelity of 99.97% and an average coherent transfer fidelity of 99.4%. Our results provide key elements for high-fidelity, on-chip quantum information distribution, as long envisaged, reinforcing the scaling prospects of silicon-based spin qubits.
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Geyer, Simon, Bence Hetényi, Stefano Bosco, Leon C. Camenzind, Rafael S. Eggli, Andreas Fuhrer, Daniel Loss, Richard J. Warburton, Dominik M. Zumbühl, and Andreas V. Kuhlmann. "Anisotropic exchange interaction of two hole-spin qubits." Nature Physics, May 6, 2024. http://dx.doi.org/10.1038/s41567-024-02481-5.
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AbstractSemiconductor spin qubits offer the potential to employ industrial transistor technology to produce large-scale quantum computers. Silicon hole spin qubits benefit from fast all-electrical qubit control and sweet spots to counteract charge and nuclear spin noise. However, the demonstration of a two-qubit interaction has remained an open challenge. One missing factor is an understanding of the exchange coupling in the presence of a strong spin–orbit interaction. Here we study two hole-spin qubits in a silicon fin field-effect transistor, the workhorse device of today’s semiconductor industry. We demonstrate electrical tunability of the exchange splitting from above 500 MHz to close-to-off and perform a conditional spin-flip in 24 ns. The exchange is anisotropic because of the spin–orbit interaction. Upon tunnelling from one quantum dot to the other, the spin is rotated by almost 180 degrees. The exchange Hamiltonian no longer has the Heisenberg form and can be engineered such that it enables two-qubit controlled rotation gates without a trade-off between speed and fidelity. This ideal behaviour applies over a wide range of magnetic field orientations, rendering the concept robust with respect to variations from qubit to qubit, indicating that it is a suitable approach for realizing a large-scale quantum computer.
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van Riggelen, F., W. I. L. Lawrie, M. Russ, N. W. Hendrickx, A. Sammak, M. Rispler, B. M. Terhal, G. Scappucci, and M. Veldhorst. "Phase flip code with semiconductor spin qubits." npj Quantum Information 8, no. 1 (October 27, 2022). http://dx.doi.org/10.1038/s41534-022-00639-8.
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AbstractThe fault-tolerant operation of logical qubits is an important requirement for realizing a universal quantum computer. Spin qubits based on quantum dots have great potential to be scaled to large numbers because of their compatibility with standard semiconductor manufacturing. Here, we show that a quantum error correction code can be implemented using a four-qubit array in germanium. We demonstrate a resonant SWAP gate and by combining controlled-Z and controlled-S−1 gates we construct a Toffoli-like three-qubit gate. We execute a two-qubit phase flip code and find that we can preserve the state of the data qubit by applying a refocusing pulse to the ancilla qubit. In addition, we implement a phase flip code on three qubits, making use of a Toffoli-like gate for the final correction step. Both the quality and quantity of the qubits will require significant improvement to achieve fault-tolerance. However, the capability to implement quantum error correction codes enables co-design development of quantum hardware and software, where codes tailored to the properties of spin qubits and advances in fabrication and operation can now come together to advance semiconductor quantum technology.
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van Riggelen-Doelman, Floor, Chien-An Wang, Sander L. de Snoo, William I. L. Lawrie, Nico W. Hendrickx, Maximilian Rimbach-Russ, Amir Sammak, Giordano Scappucci, Corentin Déprez, and Menno Veldhorst. "Coherent spin qubit shuttling through germanium quantum dots." Nature Communications 15, no. 1 (July 8, 2024). http://dx.doi.org/10.1038/s41467-024-49358-y.
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AbstractQuantum links can interconnect qubit registers and are therefore essential in networked quantum computing. Semiconductor quantum dot qubits have seen significant progress in the high-fidelity operation of small qubit registers but establishing a compelling quantum link remains a challenge. Here, we show that a spin qubit can be shuttled through multiple quantum dots while preserving its quantum information. Remarkably, we achieve these results using hole spin qubits in germanium, despite the presence of strong spin-orbit interaction. In a minimal quantum dot chain, we accomplish the shuttling of spin basis states over effective lengths beyond 300 microns and demonstrate the coherent shuttling of superposition states over effective lengths corresponding to 9 microns, which we can extend to 49 microns by incorporating dynamical decoupling. These findings indicate qubit shuttling as an effective approach to route qubits within registers and to establish quantum links between registers.
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De Michielis, Marco, Davide Rei, and Elena Ferraro. "Parallel Gate Fidelity of Flip‐Flop Qubits in Small 1D‐ and 2D‐Arrays in a Noisy Environment." Advanced Quantum Technologies, April 28, 2024. http://dx.doi.org/10.1002/qute.202300455.
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AbstractThe long coherence time of donor atom nuclear spin states and of its bounded electron in can be exploited to define a qubit. This work is focused on a type of donor‐ and quantum dot‐based qubit, the flip‐flop (FF) qubit, that leverages antiparallel electron‐nuclear spin states of a donor atom controlled by an electric field. It can provide long‐range inter‐qubit interactions in the order of some hundreds of nanometers, thus relaxing the common constraints and tolerances on inter‐qubit distances in donor‐based qubits. Simulation results of linear array (LA) and square array (SA) of four FF qubits are presented to study the effect of noise, idle qubits, and simultaneous gating (parallel gating) on gate fidelity. The impact of noise and qubit mutual coupling for both considered types of array are presented and the obtained fidelity results are compared.
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Arısoy, Onat, and Özgür E. Müstecaplıoğlu. "Few-qubit quantum refrigerator for cooling a multi-qubit system." Scientific Reports 11, no. 1 (June 21, 2021). http://dx.doi.org/10.1038/s41598-021-92258-0.
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AbstractWe propose to use a few-qubit system as a compact quantum refrigerator for cooling an interacting multi-qubit system. We specifically consider a central qubit coupled to N ancilla qubits in a so-called spin-star model to be used as refrigerant by means of short interactions with a many-qubit system to be cooled. We first show that if the interaction between the qubits is of the longitudinal and ferromagnetic Ising model form, the central qubit is colder than the environment. We summarize how preparing the refrigerant qubits using the spin-star model paves the way for the cooling of a many-qubit system by means of a collisional route to thermalization. We discuss a simple refrigeration cycle, considering the operation cost and cooling efficiency, which can be controlled by N and the qubit–qubit interaction strength. Besides, bounds on the achievable temperature are established. Such few-qubit compact quantum refrigerators can be significant to reduce dimensions of quantum technology applications, can be easy to integrate into all-qubit systems, and can increase the speed and power of quantum computing and thermal devices.
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Feng, MengKe, Lin Htoo Zaw, and Teck Seng Koh. "Two-qubit sweet spots for capacitively coupled exchange-only spin qubits." npj Quantum Information 7, no. 1 (July 16, 2021). http://dx.doi.org/10.1038/s41534-021-00449-4.
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AbstractThe implementation of high fidelity two-qubit gates is a bottleneck in the progress toward universal quantum computation in semiconductor quantum dot qubits. We study capacitive coupling between two triple quantum dot spin qubits encoded in the S = 1/2, Sz = −1/2 decoherence-free subspace—the exchange-only (EO) spin qubits. We report exact gate sequences for CPHASE and CNOT gates, and demonstrate theoretically, the existence of multiple two-qubit sweet spots (2QSS) in the parameter space of capacitively coupled EO qubits. Gate operations have the advantage of being all-electrical, but charge noise that couple to electrical parameters of the qubits cause decoherence. Assuming noise with a 1/f spectrum, two-qubit gate fidelities and times are calculated, which provide useful information on the noise threshold necessary for fault-tolerance. We study two-qubit gates at single and multiple parameter 2QSS. In particular, for two existing EO implementations—the resonant exchange (RX) and the always-on exchange-only (AEON) qubits—we compare two-qubit gate fidelities and times at positions in parameter space where the 2QSS are simultaneously single-qubit sweet spots (1QSS) for the RX and AEON. These results provide a potential route to the realization of high fidelity quantum computation.
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Wang, Xin, Edwin Barnes, and S. Das Sarma. "Improving the gate fidelity of capacitively coupled spin qubits." npj Quantum Information 1, no. 1 (October 27, 2015). http://dx.doi.org/10.1038/npjqi.2015.3.
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AbstractCapacitively coupled semiconductor spin qubits hold promise as the building blocks of a scalable quantum computing architecture with long-range coupling between distant qubits. However, the two-qubit gate fidelities achieved in experiments to date have been severely limited by decoherence originating from charge noise and hyperfine interactions with nuclear spins, and are currently unacceptably low for any conceivable multi-qubit gate operations. Here, we present control protocols that implement two-qubit entangling gates while substantially suppressing errors due to both types of noise. These protocols are obtained by making simple modifications to control sequences already used in the laboratory and should thus be easy enough for immediate experimental realisation. Together with existing control protocols for robust single-qubit gates, our results constitute an important step toward scalable quantum computation using spin qubits in semiconductor platforms.
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Piot, N., B. Brun, V. Schmitt, S. Zihlmann, V. P. Michal, A. Apra, J. C. Abadillo-Uriel, et al. "A single hole spin with enhanced coherence in natural silicon." Nature Nanotechnology, September 22, 2022. http://dx.doi.org/10.1038/s41565-022-01196-z.
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AbstractSemiconductor spin qubits based on spin–orbit states are responsive to electric field excitations, allowing for practical, fast and potentially scalable qubit control. Spin electric susceptibility, however, renders these qubits generally vulnerable to electrical noise, which limits their coherence time. Here we report on a spin–orbit qubit consisting of a single hole electrostatically confined in a natural silicon metal-oxide-semiconductor device. By varying the magnetic field orientation, we reveal the existence of operation sweet spots where the impact of charge noise is minimized while preserving an efficient electric-dipole spin control. We correspondingly observe an extension of the Hahn-echo coherence time up to 88 μs, exceeding by an order of magnitude existing values reported for hole spin qubits, and approaching the state-of-the-art for electron spin qubits with synthetic spin–orbit coupling in isotopically purified silicon. Our finding enhances the prospects of silicon-based hole spin qubits for scalable quantum information processing.
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Kojima, Y., T. Nakajima, A. Noiri, J. Yoneda, T. Otsuka, K. Takeda, S. Li, et al. "Probabilistic teleportation of a quantum dot spin qubit." npj Quantum Information 7, no. 1 (May 6, 2021). http://dx.doi.org/10.1038/s41534-021-00403-4.
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AbstractElectron spins in semiconductor quantum dots have been intensively studied for implementing quantum computation and high-fidelity single- and two-qubit operations have recently been achieved. Quantum teleportation is a three-qubit protocol exploiting quantum entanglement and it serves as an essential primitive for more sophisticated quantum algorithms. Here we demonstrate a scheme for quantum teleportation based on direct Bell measurement for a single-electron spin qubit in a triple quantum dot utilizing the Pauli exclusion principle to create and detect maximally entangled states. The single spin polarization is teleported from the input qubit to the output qubit. We find this fidelity is primarily limited by singlet–triplet mixing, which can be improved by optimizing the device parameters. Our results may be extended to quantum algorithms with a larger number of semiconductor spin qubits.
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Hu, Ye-Bin, Rong Chen, Guo-Qing Yan, and Xing-Yu Zhu. "Long-range entanglement between spin qubits in quantum dots by virtual photon process." Modern Physics Letters A, July 7, 2023. http://dx.doi.org/10.1142/s0217732323500530.
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Electron spin qubits in silicon quantum dots are an attractive candidate for large-scalable quantum computation. An essential step for quantum information processing based on spin qubits is to realize the spatially separated two-qubit gate and entanglement with high fidelity. Here, we consider two spin qubits coupled to a common superconducting resonator in circuit quantum electrodynamics. We investigate the long-range two-qubit iSWAP gate mediated by virtual microwave photons using a Gaussian smoothing pulse. We show that the entangling gate fidelity can reach [Formula: see text] under realistic experimental conditions and analyze the factors limiting gate fidelity. Moreover, we numerically demonstrate the generation of remote Bell entangled states of spin qubits with high fidelity. In addition, this spin–resonator architecture can be used to implement quantum algorithms using our scheme. These results pave the way for quantum information processing with spin qubits.