Journal articles: 'Dynamic Decoherence Control'

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Hu, Juju, Qiang Ke, and Yinghua Ji. "Dynamical decoupling with initial system-environment correlations." International Journal of Modern Physics B 35, no. 05 (January 29, 2021): 2150068. http://dx.doi.org/10.1142/s0217979221500685.

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Dynamical decoupling (DD) technique is one of the most successful methods to suppress decoherence in qubit systems. In this paper, we studied a solvable pure dephasing model and investigated how DD sequences and initial correlations affect this system. We gave the analytical expressions of decoherence functions and compared the decoherence suppression effects of DD pulses in Ohmic, sub-Ohmic and super-Ohmic environments. Our results show that (1) The initial system-environment correlation will cause additional decoherence. In order to control the dynamic process of open quantum system more accurately and effectively, the initial correlation between the system and reservoir must be considered. (2) High frequency DD pulses can significantly reduce the amplitude of the decoherence function even in the presence of initial system-environment correlations.

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Wei, Wenzhe, Peng Hao, Zhiyu Ma, Huixing Zhang, Liren Pang, Fangfei Wu, Ke Deng, Jie Zhang, and Zehuang Lu. "Measurement and suppression of magnetic field noise of trapped ion qubit." Journal of Physics B: Atomic, Molecular and Optical Physics 55, no. 7 (April 6, 2022): 075001. http://dx.doi.org/10.1088/1361-6455/ac5e7d.

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Abstract Magnetic field noise is an important factor causing quantum decoherence in quantum systems. In order to suppress the decoherence effect, magnetic field noise needs to be properly measured and controlled. Magnetic field noise power spectrum measurement using a single trapped ion based quantum spectrum analyzer is a very effective way. In this paper, the magnetic field noise measurement based on dynamic decoupling technique is analyzed theoretically. Furthermore, we use magnetically insensitive transition to measure the magnetic field noise, which has the potential to measure stronger magnetic field noise and speed up the measurement process. In our experiment, we suppress the magnetic field noise by using active feedback control and passive compensation, where the required passive compensation amplitude is obtained by measuring the magnetic field noise spectrum of a single 25Mg+ ion. With the magnetic field noise suppressed, the expected contribution of the magnetic field noise to the stability of the 25Mg+–27Al+ ion optical clock can be decreased from 2.8 × 1 0 − 15 / τ to 7.2 × 1 0 − 16 / τ .

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Liu, Zheng, Ye-Xin Wang, Yu-Hui Fang, Si-Xue Qin, Zhe-Ming Wang, Shang-Da Jiang, and Song Gao. "Electric field manipulation enhanced by strong spin-orbit coupling: promoting rare-earth ions as qubits." National Science Review 7, no. 10 (June 27, 2020): 1557–63. http://dx.doi.org/10.1093/nsr/nwaa148.

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Abstract Quantum information processing based on magnetic ions has potential for applications as the ions can be modified in their electronic properties and assembled by a variety of chemical methods. For these systems to achieve individual spin addressability and high energy efficiency, we exploited the electric field as a tool to manipulate the quantum behaviours of the rare-earth ion which has strong spin-orbit coupling. A Ce:YAG single crystal was employed with considerations to the dynamics and the symmetry requirements. The Stark effect of the Ce3+ ion was observed and measured. When demonstrated as a quantum phase gate, the electric field manipulation exhibited high efficiency which allowed up to 57 π/2 operations before decoherence with optimized field direction. It was also utilized to carry out quantum bang-bang control, as a method of dynamic decoupling, and the refined Deutsch-Jozsa algorithm. Our experiments highlighted rare-earth ions as potentially applicable qubits because they offer enhanced spin-electric coupling which enables high-efficiency quantum manipulation.

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Khaneja, Navin. "Cone separation, quadratic control systems and control of spin dynamics in the presence of decoherence." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 375, no. 2088 (March 6, 2017): 20160214. http://dx.doi.org/10.1098/rsta.2016.0214.

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In this paper, we study some control problems related to the control of coupled spin dynamics in the presence of relaxation and decoherence in nuclear magnetic resonance spectroscopy. The decoherence is modelled through a master equation. We study some model problems, whereby, through an appropriate choice of state variables, the system is reduced to a control system, where the state enters linearly and controls quadratically. We study this quadratic control system. Study of this system gives us explicit bounds on how close a coupled spin system can be driven to its target state and how much coherence and polarization can be transferred between coupled spins. Optimal control for the quadratic control system can be understood as the separation of closed cones, and we show how the derived results on optimal efficiency can be interpreted in this formulation. Finally, we study some finite-time optimal control problems for the quadratic control system. This article is part of the themed issue ‘Horizons of cybernetical physics’.

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Mohamed, Abdel-Baset A., Eied M. Khalil, Mahmoud M. Selim, and Hichem Eleuch. "Quantum Fisher Information and Bures Distance Correlations of Coupled Two Charge-Qubits Inside a Coherent Cavity with the Intrinsic Decoherence." Symmetry 13, no. 2 (February 22, 2021): 352. http://dx.doi.org/10.3390/sym13020352.

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The dynamics of two charged qubits containing Josephson Junctions inside a cavity are investigated under the intrinsic decoherence effect. New types of quantum correlations via local quantum Fisher information and Bures distance norm are explored. We show that we can control the quantum correlations robustness by the intrinsic decoherence rate, the qubit-qubit coupling as well as by the initial coherent states superposition. The phenomenon of sudden changes and the freezing behavior for the local quantum Fisher information are sensitive to the initial coherent state superposition and the intrinsic decoherence.

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WANG, LI, TAO TU, GUO-PING GUO, and GUANG-CAN GUO. "INTRINSIC AND EXTRINSIC DECOHERENCE FOR CHARGE QUBIT DYNAMICS IN A DOUBLE QUANTUM DOT." Modern Physics Letters B 28, no. 02 (January 8, 2014): 1450014. http://dx.doi.org/10.1142/s0217984914500146.

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In this paper, we investigate different decoherence sources with a charge qubit in a semiconductor quantum dot device. We distinguish between the intrinsic qubit population leakage and extrinsic environment noise, through a crucial difference in their signatures on the dynamics of the qubit. The results demonstrated here could help to develop unified understanding of decoherence mechanism in quantum dots and allow us to design suitable protocols for control and measurement.

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Aravena, Daniel, and Eliseo Ruiz. "Spin dynamics in single-molecule magnets and molecular qubits." Dalton Transactions 49, no. 29 (2020): 9916–28. http://dx.doi.org/10.1039/d0dt01414a.

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PRIVMAN, VLADIMIR. "SHORT-TIME DECOHERENCE AND DEVIATION FROM PURE QUANTUM STATES." Modern Physics Letters B 16, no. 13 (June 10, 2002): 459–65. http://dx.doi.org/10.1142/s0217984902003920.

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In systems considered for quantum computing, i.e., for control of quantum dynamics with the goal of processing information coherently, decoherence and deviation from pure quantum states, are the main obstacles to error correction. At low temperatures, usually assumed in quantum computing designs, some of the accepted approaches to evaluation of relaxation mechanisms break down. We develop a new formalism for the estimation of decoherence at short times, appropriate for evaluation of quantum computing architectures.

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LIU, REN-BAO, WANG YAO, and L. J. SHAM. "CONTROL OF ELECTRON SPIN DECOHERENCE IN MESOSCOPIC NUCLEAR SPIN BATHS." International Journal of Modern Physics B 22, no. 01n02 (January 20, 2008): 27–32. http://dx.doi.org/10.1142/s0217979208046013.

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The electron spin decoherence by nuclear spins in semiconductor quantum dots is caused by quantum entanglement between the electron and the nuclei. The many-body dynamics problem of the interacting nuclear spins can be solved with the pair-correlation approximation which treats the nuclear spin flip-flops as mutually independent. The nuclear spin dynamics can be controlled by simply flipping the electron spin so that the electron is disentangled from the nuclei and hence its lost coherence is restored.

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Mohamed, Abdel-Baset A., Hichem Eleuch, and Abdel-Shafy F. Obada. "Influence of the Coupling between Two Qubits in an Open Coherent Cavity: Nonclassical Information via Quasi-Probability Distributions." Entropy 21, no. 12 (November 21, 2019): 1137. http://dx.doi.org/10.3390/e21121137.

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In this paper, we investigate the dynamics of two coupled two-level systems (or qubits) that are resonantly interacting with a microwave cavity. We examine the effects of the intrinsic decoherence rate and the coupling between the two qubits on the non-classicality of different system partitions via quasi-probability functions. New definitions for the partial Q-function and its Wehrl entropy are used to investigate the information and the quantum coherence of the phase space. The amount of the quantum coherence and non-classicality can be appropriately tuned by suitably adopting the rates of the intrinsic-decoherence and the coupling between the two qubits. The intrinsic decoherence has a pronounced effect on the negativity and the positivity of the Wigner function. The coupling between the two qubits can control the negativity and positivity of the quasi-probability functions.

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Milburn, G. J. "Decoherence and the conditions for the classical control of quantum systems." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 370, no. 1975 (September 28, 2012): 4469–86. http://dx.doi.org/10.1098/rsta.2011.0487.

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We find the conditions for one quantum system to function as a classical controller of another quantum system: the controller must be an open system and rapidly diagonalized in the diagonal basis of the controller variable that is coupled to the controlled system. This causes decoherence in the controlled system that can be made small if the rate of diagonalization is fast. We give a detailed example based on the quantum optomechanical control of a mechanical resonator. The resulting equations are structurally similar to recently proposed models for consistently combining quantum and classical stochastic dynamics.

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Shuang, Feng, and Herschel Rabitz. "Cooperating or fighting with decoherence in the optimal control of quantum dynamics." Journal of Chemical Physics 124, no. 15 (April 21, 2006): 154105. http://dx.doi.org/10.1063/1.2186644.

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Lara-Astiaso, Manuel, David Ayuso, Ivano Tavernelli, Piero Decleva, Alicia Palacios, and Fernando Martín. "Decoherence, control and attosecond probing of XUV-induced charge migration in biomolecules. A theoretical outlook." Faraday Discussions 194 (2016): 41–59. http://dx.doi.org/10.1039/c6fd00074f.

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The sudden ionization of a molecule by an attosecond pulse is followed by charge redistribution on a time scale from a few femtoseconds down to hundreds of attoseconds. This ultrafast redistribution is the result of the coherent superposition of electronic continua associated with the ionization thresholds that are reached by the broadband attosecond pulse. Thus, a correct theoretical description of the time evolution of the ensuing wave packet requires the knowledge of the actual ionization amplitudes associated with all open ionization channels, a real challenge for large and medium-size molecules. Recently, the first calculation of this kind has come to light, allowing for interpretation of ultrafast electron dynamics observed in attosecond pump–probe experiments performed on the amino acid phenylalanine [Calegari et al., Science 2014, 346, 336]. However, as in most previous theoretical works, the interpretation was based on various simplifying assumptions, namely, the ionized electron was not included in the description of the cation dynamics, the nuclei were fixed at their initial position during the hole migration process, and the effect of the IR probe pulse was ignored. Here we go a step further and discuss the consequences of including these effects in the photoionization of the glycine molecule. We show that (i) the ionized electron does not affect hole dynamics beyond the first femtosecond, and (ii) nuclear dynamics has only a significant effect after approximately 8 fs, but does not destroy the coherent motion of the electronic wave packet during at least few additional tens of fs. As a first step towards understanding the role of the probe pulse, we have considered an XUV probe pulse, instead of a strong IR one, and show that such an XUV probe does not introduce significant distortions in the pump-induced dynamics, suggesting that pump–probe strategies are suitable for imaging and manipulating charge migration in complex molecules. Furthermore, we show that hole dynamics can be changed by shaping the attosecond pump pulse, thus opening the door to the control of charge dynamics in biomolecules.

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Gherardini, Stefano, Andrea Smirne, Matthias M. Müller, and Filippo Caruso. "Advances in Sequential Measurement and Control of Open Quantum Systems." Proceedings 12, no. 1 (June 24, 2019): 11. http://dx.doi.org/10.3390/proceedings2019012011.

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Novel concepts, perspectives and challenges in measuring and controlling an open quantum system via sequential schemes are shown. We discuss how similar protocols, relying both on repeated quantum measurements and dynamical decoupling control pulses, can allow to: (i) Confine and protect quantum dynamics from decoherence in accordance with the Zeno physics. (ii) Analytically predict the probability that a quantum system is transferred into a target quantum state by means of stochastic sequential measurements. (iii) Optimally reconstruct the spectral density of environmental noise sources by orthogonalizing in the frequency domain the filter functions driving the designed quantum-sensor. The achievement of these tasks will enhance our capability to observe and manipulate open quantum systems, thus bringing advances to quantum science and technologies.

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Giorgi, Gian, Salvatore Lorenzo, and Stefano Longhi. "Topological Protection and Control of Quantum Markovianity." Photonics 7, no. 1 (February 8, 2020): 18. http://dx.doi.org/10.3390/photonics7010018.

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Under the Born–Markov approximation, a qubit system, such as a two-level atom, is known to undergo a memoryless decay of quantum coherence or excitation when weakly coupled to a featureless environment. Recently, it has been shown that unavoidable disorder in the environment is responsible for non-Markovian effects and information backflow from the environment into the system owing to Anderson localization. This turns disorder into a resource for enhancing non-Markovianity in the system–environment dynamics, which could be of relevance in cavity quantum electrodynamics. Here we consider the decoherence dynamics of a qubit weakly coupled to a two-dimensional bath with a nontrivial topological phase, such as a two-level atom embedded in a two-dimensional coupled-cavity array with a synthetic gauge field realizing a quantum-Hall bath, and show that Markovianity is protected against moderate disorder owing to the robustness of chiral edge modes in the quantum-Hall bath. Interestingly, switching off the gauge field, i.e., flipping the bath into a topological trivial phase, allows one to re-introduce non-Markovian effects. Such a result indicates that changing the topological phase of a bath by a tunable synthetic gauge field can be harnessed to control non-Markovian effects and quantum information backflow in a qubit-environment system.

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Zhang, Xiong-Peng, Bin Shao, and Jian Zou. "Investigating the lower bound of minimum gate times using optimal control." Modern Physics Letters B 32, no. 27 (September 27, 2018): 1850322. http://dx.doi.org/10.1142/s0217984918503220.

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Motivated by a bound derived in a recent work [C. Arenz, B. Russell, D. Burgarth and H. Rabitz, New J. Phys. 19 (2017) 103015], we apply optimal control theory to the dynamics of qubit systems, with the goal of investigating the lower bound of minimum gate times. In practice, we not only need to reach the desired unitary gates but we need to do so in a reasonable time (below the typical decoherence time). Therefore, we employ the recently introduced lower bound to estimate the minimum gate time and resort to numerical gate optimization in order to study the tightness of the obtained bound and our findings verify the relationship between the internal Hamiltonian and the minimum evolution time remarkably well. Finally, we discuss both challenges and ways forward for obtaining the same efficacy under realistic conditions.

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Liu, Ren-Bao, Wang Yao, and L. J. Sham. "Control of electron spin decoherence caused by electron–nuclear spin dynamics in a quantum dot." New Journal of Physics 9, no. 7 (July 11, 2007): 226. http://dx.doi.org/10.1088/1367-2630/9/7/226.

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Yang, Yu-Feng, Ye-Hong Chen, Qi-Cheng Wu, Zhi-Cheng Shi, Jie Song, and Yan Xia. "High-fidelity generating multi-qubit W state via dressed states in the system of multiple resonators coupled with a superconducting qubit." Canadian Journal of Physics 96, no. 1 (January 2018): 81–89. http://dx.doi.org/10.1139/cjp-2017-0227.

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In this paper, we present an alternative scheme to generate W state of three superconducting qubits in three spatially separated coplanar waveguide resonators with the quantum Zeno dynamics and the dressed states. When a set of dressed states is suitably chosen, a scheme can be designed for accelerating the adiabatic passage without additional couplings. What is more, the populations of the intermediate states of the system can be restricted by choosing suitable control parameters. We discuss the influence of dissipation and operational imperfection by numerical analysis and the results show that the scheme is robust against various decoherence processes. In addition, we hope the scheme can provide a theoretical basis for the manipulation of the multi-qubit quantum state.

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Li, Boxi, Shahnawaz Ahmed, Sidhant Saraogi, Neill Lambert, Franco Nori, Alexander Pitchford, and Nathan Shammah. "Pulse-level noisy quantum circuits with QuTiP." Quantum 6 (January 24, 2022): 630. http://dx.doi.org/10.22331/q-2022-01-24-630.

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The study of the impact of noise on quantum circuits is especially relevant to guide the progress of Noisy Intermediate-Scale Quantum (NISQ) computing. In this paper, we address the pulse-level simulation of noisy quantum circuits with the Quantum Toolbox in Python (QuTiP). We introduce new tools in qutip-qip, QuTiP's quantum information processing package. These tools simulate quantum circuits at the pulse level, leveraging QuTiP's quantum dynamics solvers and control optimization features. We show how quantum circuits can be compiled on simulated processors, with control pulses acting on a target Hamiltonian that describes the unitary evolution of the physical qubits. Various types of noise can be introduced based on the physical model, e.g., by simulating the Lindblad density-matrix dynamics or Monte Carlo quantum trajectories. In particular, the user can define environment-induced decoherence at the processor level and include noise simulation at the level of control pulses. We illustrate how the Deutsch-Jozsa algorithm is compiled and executed on a superconducting-qubit-based processor, on a spin-chain-based processor and using control optimization algorithms. We also show how to easily reproduce experimental results on cross-talk noise in an ion-based processor, and how a Ramsey experiment can be modeled with Lindblad dynamics. Finally, we illustrate how to integrate these features with other software frameworks.

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Kurizki, Gershon. "Universal Dynamical Control of Open Quantum Systems." ISRN Optics 2013 (September 19, 2013): 1–51. http://dx.doi.org/10.1155/2013/783865.

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Due to increasing demands on speed and security of data processing, along with requirements on measurement precision in fundamental research, quantum phenomena are expected to play an increasing role in future technologies. Special attention must hence be paid to omnipresent decoherence effects, which hamper quantumness. Their consequence is always a deviation of the quantum state evolution (error) with respect to the expected unitary evolution if these effects are absent. In operational tasks such as the preparation, transformation, transmission, and detection of quantum states, these effects are detrimental and must be suppressed by strategies known as dynamical decoupling, or the more general dynamical control by modulation developed by us. The underlying dynamics must be Zeno-like, yielding suppressed coupling to the bath. There are, however, tasks which cannot be implemented by unitary evolution, in particular those involving a change of the system’s state entropy. Such tasks necessitate efficient coupling to a bath for their implementation. Examples include the use of measurements to cool (purify) a system, to equilibrate it, or to harvest and convert energy from the environment. If the underlying dynamics is anti-Zeno like, enhancement of this coupling to the bath will occur and thereby facilitate the task, as discovered by us. A general task may also require state and energy transfer, or entanglement of noninteracting parties via shared modes of the bath which call for maximizing the shared (two-partite) couplings with the bath, but suppressing the single-partite couplings. For such tasks, a more subtle interplay of Zeno and anti-Zeno dynamics may be optimal. We have therefore constructed a general framework for optimizing the way a system interacts with its environment to achieve a desired task. This optimization consists in adjusting a given “score” that quantifies the success of the task, such as the targeted fidelity, purity, entropy, entanglement, or energy by dynamical modification of the system-bath coupling spectrum on demand.

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Norcia, Matthew A., Robert J. Lewis-Swan, Julia R. K. Cline, Bihui Zhu, Ana M. Rey, and James K. Thompson. "Cavity-mediated collective spin-exchange interactions in a strontium superradiant laser." Science 361, no. 6399 (July 19, 2018): 259–62. http://dx.doi.org/10.1126/science.aar3102.

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Laser-cooled and quantum degenerate atoms are being pursued as quantum simulators and form the basis of today’s most precise sensors. A key challenge toward these goals is to understand and control coherent interactions between the atoms. We observe long-range exchange interactions mediated by an optical cavity, which manifest as tunable spin-spin interactions on the pseudo spin-½ system composed of the millihertz linewidth clock transition in strontium. This leads to one-axis twisting dynamics, the emergence of a many-body energy gap, and gap protection of the optical coherence against certain sources of decoherence. Our observations will aid in the future design of versatile quantum simulators and the next generation of atomic clocks that use quantum correlations for enhanced metrology.

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CAMACHO B., A. S., and R. M. GUTIERREZ. "COHERENT DYNAMICS OF AN ASYMMETRIC DOUBLE QUANTUM WELL." Surface Review and Letters 09, no. 05n06 (October 2002): 1623–30. http://dx.doi.org/10.1142/s0218625x02004104.

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Coherent optical effects coming from two excited levels in an engineered asymmetric double quantum well have been detected with duration of picoseconds.1 This short decoherence time is related with the dephasing time. Although dephasing is mainly due to electron–electron scattering and LO phonons in polar semiconductor provide the dominant inelastic scattering mechanism, a study of the elastic scattering with phonons during the coherent stage is also needed to understand the coherent electron dynamics. In this work is presented a microscopic study of the elastic scattering rates due to electron–LO-phonon interaction, which are obtained for each of the three conduction subbands on a tailored double asymmetric quantum well by using the imaginary part of the polaron self-energy within a many-body formalism. Both absorption and emission rates are calculated. The dephasing times for different electronic states in a given heterostructure can be very different, depending on the material, geometry, temperature, carrier density, etc. As an important geometric parameter is chosen the barrier width, which tunes the energy differences between the two upper levels or tunneling times. Electron density effect is studied through screening. Two limits are presented — unscreened and static screening. It is found that after an ultrashort pulse the absorption and emission scattering rates in each level are very different from the scattering rates in equilibrium and that screening effects can be used as coherent control mechanism.

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Trabattoni, A., M. Galli, M. Lara-Astiaso, A. Palacios, J. Greenwood, I. Tavernelli, P. Decleva, M. Nisoli, F. Martín, and F. Calegari. "Charge migration in photo-ionized aromatic amino acids." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 377, no. 2145 (April 2019): 20170472. http://dx.doi.org/10.1098/rsta.2017.0472.

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Attosecond pump–probe spectroscopy is a unique tool for the direct observation of the light-activated electronic motion in molecules and it offers the possibility to capture the first instants of a chemical reaction. Recently, advances in attosecond technology allowed the charge migration processes to be revealed in biochemically relevant molecules. Although this purely electronic process might be key for a future chemistry at the electron time scale, the influence of this ultrafast charge flow on the reactivity of a molecule is still debated. In this work, we exploit extreme ultraviolet attosecond pulses to activate charge migration in two aromatic amino acids, namely phenylalanine and tryptophan. Advanced numerical calculations are performed to interpret the experimental data and to discuss the effects of the nuclear dynamics on the activated quantum coherences. By comparing the experimental results obtained in the two molecules, we show that the presence of different functional groups strongly affects the fragmentation pathways, as well as the charge rearrangement. The observed charge dynamics indeed present peculiar aspects, including characteristic periodicities and decoherence times. Numerical results indicate that, even for a very large molecule such as tryptophan, the quantum coherences can survive the nuclear dynamics for several femtoseconds. These results open new and important perspectives for a deeper understanding of the photo-induced charge dynamics, as a promising tool to control the reactivity of bio-relevant molecules via photo-excitation. This article is part of the theme issue ‘Measurement of ultrafast electronic and structural dynamics with X-rays’.

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Huang, Peihao, and Xuedong Hu. "Spin manipulation and decoherence in a quantum dot mediated by a synthetic spin–orbit coupling of broken T-symmetry." New Journal of Physics 24, no. 1 (December 30, 2021): 013002. http://dx.doi.org/10.1088/1367-2630/ac430c.

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Abstract The electrical control of a spin qubit in a quantum dot (QD) relies on spin–orbit coupling (SOC), which could be either intrinsic to the underlying crystal lattice or heterostructure, or extrinsic via, for example, a micro-magnet. In experiments, micromagnets have been used as a synthetic SOC to enable strong coupling of a spin qubit in quantum dots with electric fields. Here we study theoretically the spin relaxation, pure dephasing, spin manipulation, and spin–photon coupling of an electron in a QD due to the synthetic SOC induced spin–orbit mixing. We find qualitative difference in the spin dynamics in the presence of a synthetic SOC compared with the case of the intrinsic SOC. Specifically, spin relaxation due to the synthetic SOC and deformation potential phonon emission (or Johnson noise) shows B 0 5 (or B 0) dependence with the magnetic field, which is in contrast with the B 0 7 (or B 0 3 ) dependence in the case of the intrinsic SOC. Moreover, charge noise induces fast spin dephasing to the first order of the synthetic SOC, which is in sharp contrast with the negligible spin pure dephasing in the case of the intrinsic SOC. These qualitative differences are attributed to the broken time-reversal symmetry (T-symmetry) of the synthetic SOC. An SOC with broken T-symmetry (such as the synthetic SOC from a micro-magnet) eliminates the ‘Van Vleck cancellation’ and causes a finite longitudinal spin–electric coupling that allows the longitudinal coupling between spin and electric field, and in turn allows spin pure dephasing. Finally, through proper choice of magnetic field orientation, the electric-dipole spin resonance via the synthetic SOC can be improved with potential applications in spin-based quantum computing.

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Fraval, E., M. J. Sellars, and J. J. Longdell. "Dynamic Decoherence Control of a Solid-State Nuclear-Quadrupole Qubit." Physical Review Letters 95, no. 3 (July 15, 2005). http://dx.doi.org/10.1103/physrevlett.95.030506.

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Busto, David, Hugo Laurell, Daniel Finkelstein-Shapiro, Christiana Alexandridi, Marcus Isinger, Saikat Nandi, Richard J. Squibb, et al. "Probing electronic decoherence with high-resolution attosecond photoelectron interferometry." European Physical Journal D 76, no. 7 (July 2022). http://dx.doi.org/10.1140/epjd/s10053-022-00438-y.

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Abstract Quantum coherence plays a fundamental role in the study and control of ultrafast dynamics in matter. In the case of photoionization, entanglement of the photoelectron with the ion is a well-known source of decoherence when only one of the particles is measured. Here, we investigate decoherence due to entanglement of the radial and angular degrees of freedom of the photoelectron. We study two-photon ionization via the 2s2p autoionizing state in He using high spectral resolution photoelectron interferometry. Combining experiment and theory, we show that the strong dipole coupling of the 2s2p and 2p$$^2$$ 2 states results in the entanglement of the angular and radial degrees of freedom. This translates, in angle-integrated measurements, into a dynamic loss of coherence during autoionization. Graphic Abstract

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Bar-Gill, Nir, Gershon Kurizki, Markus Oberthaler, and Nir Davidson. "Dynamic control and probing of many-body decoherence in double-well Bose-Einstein condensates." Physical Review A 80, no. 5 (November 16, 2009). http://dx.doi.org/10.1103/physreva.80.053613.

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Yan, Ying, Chunyan Shi, Adam Kinos, Hafsa Syed, Sebastian P. Horvath, Andreas Walther, Lars Rippe, Xi Chen, and Stefan Kröll. "Experimental implementation of precisely tailored light-matter interaction via inverse engineering." npj Quantum Information 7, no. 1 (September 14, 2021). http://dx.doi.org/10.1038/s41534-021-00473-4.

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AbstractAccurate and efficient quantum control in the presence of constraints and decoherence is a requirement and a challenge in quantum information processing. Shortcuts to adiabaticity, originally proposed to speed up the slow adiabatic process, have nowadays become versatile toolboxes for preparing states or controlling the quantum dynamics. Unique shortcut designs are required for each quantum system with intrinsic physical constraints, imperfections, and noise. Here, we implement fast and robust control for the state preparation and state engineering in a rare-earth ions system. Specifically, the interacting pulses are inversely engineered and further optimized with respect to inhomogeneities of the ensemble and the unwanted interaction with other qubits. We demonstrate that our protocols surpass the conventional adiabatic schemes, by reducing the decoherence from the excited-state decay and inhomogeneous broadening. The results presented here are applicable to other noisy intermediate-scale quantum systems.

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Müller, Matthias M., Stefano Gherardini, Tommaso Calarco, Simone Montangero, and Filippo Caruso. "Information theoretical limits for quantum optimal control solutions: error scaling of noisy control channels." Scientific Reports 12, no. 1 (December 10, 2022). http://dx.doi.org/10.1038/s41598-022-25770-6.

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AbstractAccurate manipulations of an open quantum system require a deep knowledge of its controllability properties and the information content of the implemented control fields. By using tools of information and quantum optimal control theory, we provide analytical bounds (information-time bounds) to characterize our capability to control the system when subject to arbitrary sources of noise. Moreover, since the presence of an external noise field induces open quantum system dynamics, we also show that the results provided by the information-time bounds are in very good agreement with the Kofman–Kurizki universal formula describing decoherence processes. Finally, we numerically test the scaling of the control accuracy as a function of the noise parameters, by means of the dressed chopped random basis (dCRAB) algorithm for quantum optimal control.

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Jing, Jun, and Lian-Ao Wu. "One-component quantum mechanics and dynamical leakage-free paths." Scientific Reports 12, no. 1 (June 2, 2022). http://dx.doi.org/10.1038/s41598-022-13130-3.

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AbstractWe derive an exact one-component equation of motion for the probability amplitude of a target time-dependent state, and use the equation to reformulate quantum dynamics and control for both closed and open systems. Using the one-component equation, we show that an unexpected time-dependent leakage-free path can be induced and we capture a necessary quantity in determining the effect of decoherence suppression. Our control protocol based on the nonperturbative leakage elimination operator provides a unified perspective connecting some subtle, popular, and important concepts of quantum control, such as dynamical decoupling, quantum Zeno effect, and adiabatic passage. The resultant one-component equation will promise significant advantages in both quantum dynamics and control.

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31

Andreev, A. V., A. G. Balanov, T. M. Fromhold, M. T. Greenaway, A. E. Hramov, W. Li, V. V. Makarov, and A. M. Zagoskin. "Emergence and control of complex behaviors in driven systems of interacting qubits with dissipation." npj Quantum Information 7, no. 1 (January 4, 2021). http://dx.doi.org/10.1038/s41534-020-00339-1.

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AbstractProgress in the creation of large-scale, artificial quantum coherent structures demands the investigation of their nonequilibrium dynamics when strong interactions, even between remote parts, are non-perturbative. Analysis of multiparticle quantum correlations in a large system in the presence of decoherence and external driving is especially topical. Still, the scaling behavior of dynamics and related emergent phenomena are not yet well understood. We investigate how the dynamics of a driven system of several quantum elements (e.g., qubits or Rydberg atoms) changes with increasing number of elements. Surprisingly, a two-element system exhibits chaotic behaviors. For larger system sizes, a highly stochastic, far from equilibrium, hyperchaotic regime emerges. Its complexity systematically scales with the size of the system, proportionally to the number of elements. Finally, we demonstrate that these chaotic dynamics can be efficiently controlled by a periodic driving field. The insights provided by our results indicate the possibility of a reduced description for the behavior of a large quantum system in terms of the transitions between its qualitatively different dynamical regimes. These transitions are controlled by a relatively small number of parameters, which may prove useful in the design, characterization, and control of large artificial quantum structures.

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Babu, Aravind Plathanam, Jani Tuorila, and Tapio Ala-Nissila. "State leakage during fast decay and control of a superconducting transmon qubit." npj Quantum Information 7, no. 1 (February 11, 2021). http://dx.doi.org/10.1038/s41534-020-00357-z.

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AbstractSuperconducting Josephson junction qubits constitute the main current technology for many applications, including scalable quantum computers and thermal devices. Theoretical modeling of such systems is usually done within the two-level approximation. However, accurate theoretical modeling requires taking into account the influence of the higher excited states without limiting the system to the two-level qubit subspace. Here, we study the dynamics and control of a superconducting transmon using the numerically exact stochastic Liouville–von Neumann equation approach. We focus on the role of state leakage from the ideal two-level subspace for bath induced decay and single-qubit gate operations. We find significant short-time state leakage due to the strong coupling to the bath. We quantify the leakage errors in single-qubit gates and demonstrate their suppression with derivative removal adiabatic gates (DRAG) control for a five-level transmon in the presence of decoherence. Our results predict the limits of accuracy of the two-level approximation and possible intrinsic constraints in qubit dynamics and control for an experimentally relevant parameter set.

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Sung, Youngkyu, Félix Beaudoin, Leigh M. Norris, Fei Yan, David K. Kim, Jack Y. Qiu, Uwe von Lüpke, et al. "Non-Gaussian noise spectroscopy with a superconducting qubit sensor." Nature Communications 10, no. 1 (September 16, 2019). http://dx.doi.org/10.1038/s41467-019-11699-4.

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Abstract Accurate characterization of the noise influencing a quantum system of interest has far-reaching implications across quantum science, ranging from microscopic modeling of decoherence dynamics to noise-optimized quantum control. While the assumption that noise obeys Gaussian statistics is commonly employed, noise is generically non-Gaussian in nature. In particular, the Gaussian approximation breaks down whenever a qubit is strongly coupled to discrete noise sources or has a non-linear response to the environmental degrees of freedom. Thus, in order to both scrutinize the applicability of the Gaussian assumption and capture distinctive non-Gaussian signatures, a tool for characterizing non-Gaussian noise is essential. Here, we experimentally validate a quantum control protocol which, in addition to the spectrum, reconstructs the leading higher-order spectrum of engineered non-Gaussian dephasing noise using a superconducting qubit as a sensor. This first experimental demonstration of non-Gaussian noise spectroscopy represents a major step toward demonstrating a complete spectral estimation toolbox for quantum devices.

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Masuda, S., and K. Nakamura. "Fast-forward scaling theory." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 380, no. 2239 (November 7, 2022). http://dx.doi.org/10.1098/rsta.2021.0278.

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Speed is the key to further advances in technology. For example, quantum technologies, such as quantum computing, require fast manipulations of quantum systems in order to overcome the effect of decoherence. However, controlling the speed of quantum dynamics is often very difficult due to both the lack of a simple scaling property in the dynamics and the infinitely large parameter space to be explored. Therefore, protocols for speed control based on understanding of the dynamical properties of the system, such as non-trivial scaling property, are highly desirable. Fast-forward scaling theory (FFST) was originally developed to provide a way to accelerate, decelerate, stop and reverse the dynamics of quantum systems. FFST has been extended in order to accelerate quantum and classical adiabatic dynamics of various systems including cold atoms, internal state of molecules, spins and solid-state artificial atoms. This paper describes the basic concept of FFST and reviews the recent developments and its applications such as fast state-preparations, state protection and ion sorting. We introduce a method, called inter-trajectory travel, recently derived from FFST. We also point out the significance of deceleration in quantum technology. This article is part of the theme issue ‘Shortcuts to adiabaticity: theoretical, experimental and interdisciplinary perspectives’.

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Phuc, Nguyen Thanh, and Akihito Ishizaki. "Control of quantum dynamics of electron transfer in molecular loop structures: Spontaneous breaking of chiral symmetry under strong decoherence." Physical Review B 99, no. 6 (February 20, 2019). http://dx.doi.org/10.1103/physrevb.99.064301.

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Minello, Giorgia, Andrea Torsello, and Edwin R. Hancock. "Open system quantum thermodynamics of time-varying graphs." Journal of Complex Networks 8, no. 1 (February 1, 2020). http://dx.doi.org/10.1093/comnet/cnaa004.

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Abstract In this article, we present a novel analysis of time-evolving networks, based on a thermodynamic representation of graph structure. We show how to characterize the evolution of time-varying complex networks by relating major structural changes to thermodynamic phase transitions. In particular, we derive expressions for a number of different thermodynamic quantities (specifically energy, entropy and temperature), which we use to describe the evolutionary behaviour of the network system over time. Since in the real world no system is truly closed and interactions with the environment are usually strong, we assume an open nature of the system. We adopt the Schrödinger picture as the dynamical representation of the quantum system over time. First, we compute the network entropy using a recent quantum mechanical representation of graph structure, connecting the graph Laplacian to a density operator. Then, we assume the system evolves according to the Schrödinger representation, but we allow for decoherence due to the interaction with the environment in a model akin to Environment-Induced Decoherence. We simplify the model by separating its dynamics into (a) an unknown time-dependent unitary evolution plus (b) an observation/interaction process, and this is the sole cause of the changes in the eigenvalues of the density matrix of the system. This allows us to obtain a measure of energy exchange with the environment through the estimation of the hidden time-varying Hamiltonian responsible for the unitary part of the evolution. Using the thermodynamic relationship between changes in energy, entropy, pressure and volume, we recover the thermodynamic temperature. We assess the utility of the method on real-world time-varying networks representing complex systems in the financial and biological domains. We also compare and contrast the different characterizations provided by the thermodynamic variables (energy, entropy, temperature and pressure). The study shows that the estimation of the time-varying energy operator strongly characterizes different states of a time-evolving system and successfully detects critical events occurring during network evolution.

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Xiong, Heng-Na, Lingfeng Li, Zhe Sun, Zejin Yang, Zichun Le, Yixiao Huang, and Xiaoguang Wang. "Information Preservation of two qubits in a structured environment." New Journal of Physics, November 23, 2022. http://dx.doi.org/10.1088/1367-2630/aca559.

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Abstract The environment-induced decoherence of a quantum open system makes it fundamentally import to preserve the initial quantum information of the system in its steady state. Here we study information preservation of two maximally entangled qubits lying inside a photonic-crystal waveguide with semi-infinite cavity-array structure. We generalize our study to arbitrary position and arbitrary frequency detuning of the qubits. We find that for weak qubits-waveguide couplings, the information preservation greatly depends on the position and the frequency detuning of the qubits, while for strong couplings, both of these dependence is significantly weakened. Interestingly, by suitably choosing the position and the frequency of the qubits, high information preservation could be achieved for both weak and strong couplings, irrespective to Markovian or non-Markovian dynamics. Physically, we analytically verify that the ability of information preservation is indeed determined by the existence of the bound states of the entire system, but the probability of information preservation is closely related to the probability of the initial state of the qubits in the bound states. Our results provide an alternative route getting high information preservation without any external controls of the system.

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Band, Yehuda B., and Yonathan Japha. "Tuning the adiabaticity of spin dynamics in diamond nitrogen vacancy centers." Journal of Physics: Condensed Matter, March 24, 2022. http://dx.doi.org/10.1088/1361-648x/ac60d1.

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Abstract We study the spin dynamics of diamond nitrogen vacancy (NV) centers in an oscillating magnetic field along the symmetry axis of the NV in the presence of transverse magnetic fields. It is well-known that the coupling between the otherwise degenerate Zeeman levels $|M_S=\pm1\rangle$ due to strain and electric fields is responsible for a Landau-Zener process near the pseudo-crossing of the adiabatic energy levels when the axial component of the oscillating magnetic field changes sign. We derive an effective two-level Hamiltonian for the NV system that includes coupling between the two levels via virtual transitions into the third far-detuned level $|M_S=0\rangle$ induced by transverse magnetic fields. This coupling adds to the coupling due to strain and electric fields, with a phase that depends on the direction of the transverse field in the plane perpendicular to the NV axis. Hence, the {\em total coupling} of the Zeeman levels can be tuned to control the adiabaticity of spin dynamics by fully or partially compensating the effect of the strain and electric fields, or by enhancing it. Moreover, by varying the strength and direction of the transverse magnetic fields, one can determine the strength and direction of the local strain and electric fields at the position of the NV center, and even the {\em external} stress and electric field. The nuclear spin hyperfine interaction is shown to introduce a nuclear spin dependent offset of the axial magnetic field for which the pseudo-crossing occurs, while the adiabaticity remains unaffected by the nuclear spin. If the NV center is coupled to the environment, modeled by a bath with a Gaussian white noise spectrum, as appropriate for NVs near the diamond surface, then the spin dynamics is accompanied by relaxation of the Zeeman level populations and decoherence with a non-monotonic decrease of the purity of the system. The results presented here have important impact for metrology with NV centers, quantum control of spin systems in solids and coupled dynamics of spin and rotations in levitated nano-objects in the presence of magnetic fields.

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Journal articles on the topic 'Dynamic Decoherence Control'

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