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Frequency shift of an optical cavity mode due to a single-atom motion
摘要： Using quantum coherence effects, we have developed a new technique of detection of motion of single atoms or ions in an optical cavity. We have theoretically demonstrated that the presence of a single atom or ion inside cavity leads to a shift in cavity frequency and phase of transmitted probe beams. It has been shown by the use of EIT technique, the change of the phase is extremely sensitive to probe detuning in the vicinity of resonance frequency and can be in the order of 10?4.
关键词： optical cavity,frequency shift,Single-atom detector,phase shift,quantum coherence
更新于2025-09-23 15:22:29
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Experimental test of the relation between coherence and path information
摘要： Quantum coherence stemming from the superposition behaviour of a particle beyond the classical realm, serves as one of the most fundamental features in quantum mechanics. The wave-particle duality phenomenon, which shares the same origin, has a strong relationship with quantum coherence. Recently, an elegant relation between quantum coherence and path information has been theoretically derived. Here, we experimentally test such new duality by l1-norm measure and the minimum-error state discrimination. We prepare three classes of two-photon states encoded in polarisation degree of freedom, with one photon serving as the target and the other photon as the detector. We observe that wave-particle-like complementarity and Bagan’s equality, defined by the duality relation between coherence and path information, is well satisfied. Our results may shed new light on the original nature of wave-particle duality and on the applications of quantum coherence as a fundamental resource in quantum technologies.
关键词： wave-particle duality,minimum-error state discrimination,Bagan's equality,path information,quantum coherence,l1-norm measure
更新于2025-09-23 15:22:29
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Optimal distillation of quantum coherence with reduced waste of resources
摘要： We present an optimal probabilistic protocol to distill quantum coherence. Inspired by a specific entanglement distillation protocol, our main result yields a strictly incoherent operation that produces one of a family of maximally coherent states of variable dimension from any pure quantum state. We also expand this protocol to the case where it is possible, for some initial states, to avert any waste of resources as far as the output states are concerned, by exploiting an additional transformation into a suitable intermediate state. These results provide practical schemes for efficient quantum resource manipulation.
关键词： distillation,resource theory,quantum coherence,strictly incoherent operations
更新于2025-09-23 15:22:29
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Tightening the entropic uncertainty relations for multiple measurements and applying it to quantum coherence
摘要： The uncertainty principle sets limit on our ability to predict the values of two incompatible observables measured on a quantum particle simultaneously. This principle can be stated in various forms. In quantum information theory, it is expressed in terms of the entropic measures. Uncertainty bound can be altered by considering a particle as a quantum memory correlating with the primary particle. In this work, a method is provided for converting the entropic uncertainty relation in the absence of quantum memory to that in its presence. It is shown that the lower bounds obtained through the method are tighter than those having been achieved so far. The method is also used to obtain the uncertainty relations for multiple measurements in the presence of quantum memory. Also for a given state, the lower bounds on the sum of the relative entropies of unilateral coherences are provided using the uncertainty relations in the presence of quantum memory, and it is shown which one is tighter.
关键词： Quantum memory,Entropic uncertainty relations,Quantum coherence,Multiple measurements
更新于2025-09-23 15:21:21
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Persistent coherence of quantum superpositions in an optimally doped cuprate revealed by 2D spectroscopy
摘要： Quantum materials displaying intriguing magnetic and electronic properties could be key to the development of future technologies. However, it is poorly understood how the macroscopic behavior emerges in complex materials with strong electronic correlations. While measurements of the dynamics of excited electronic populations have been able to give some insight, they have largely neglected the intricate dynamics of quantum coherence. Here, we apply multidimensional coherent spectroscopy to a prototypical cuprate and report unprecedented coherent dynamics persisting for ~500 fs, originating directly from the quantum superposition of optically excited states separated by 20 to 60 meV. These results reveal that the states in this energy range are correlated with the optically excited states at ~1.5 eV and point to nontrivial interactions between quantum many-body states on the different energy scales. In revealing these dynamics and correlations, we demonstrate that multidimensional coherent spectroscopy can interrogate complex quantum materials in unprecedented ways.
关键词： multidimensional coherent spectroscopy,quantum coherence,quantum materials,electronic correlations,cuprate
更新于2025-09-23 15:21:01
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[Texts and Readings in Physical Sciences] Open Quantum Systems Volume 20 (Dynamics of Nonclassical Evolution) || Quantum Tunneling
摘要： Tunneling is a bona?de quantum mechanical e?ect [175, 176]. Since it involves barrier penetration, it is also an inherently non-perturbative process. It serves a crucial role in the test of quantum coherence in macroscopic regimes, also known as Macroscopic Quantum Coherence (MQC) [68]. Development in technology has made the concept of tunneling crucial to the development of devices on the nanoscopic, nanometre 10?9m range, and mesoscopic, upto a few microns μm, scales. Further, tunneling has important rami?cations to almost all branches of physics, such as atomic, molecular, condensed matter physics as well as to quantum ?eld theory and cosmology. A very powerful technique for dealing with tunneling is the semiclassical approximation, which we detail below. Tunneling processes can be broadly classi?ed into two categories: coherent and incoherent tunneling. Coherent tunneling phenomena involve the coherent overlap of wavefunctions located in individual domains, such as, ground states of potential wells, and separated by energy barriers. Incoherent tunneling involves scattering between reservoirs or decay of metastable states into the continuum and hence no overlap of the wavefunction. Tunneling has two perspectives: time independent energy domain considerations and that invoking the time dependent dynamics.
关键词： Macroscopic Quantum Coherence,Semiclassical Approximation,Quantum Tunneling,Incoherent Tunneling,Coherent Tunneling
更新于2025-09-23 15:21:01
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Variational approach to the optimal control of coherently driven, open quantum system dynamics
摘要： Quantum coherence inherently affects the dynamics and the performances of a quantum machine. Coherent control can, at least in principle, enhance the work extraction and boost the velocity of evolution in an open quantum system. Using advanced tools from the calculus of variations and reformulating the control problem in the instantaneous Hamiltonian eigenframe, we develop a general technique for minimizing a wide class of cost functionals when the external control has access to full rotations of the system Hamiltonian. The method is then applied both to time and heat loss minimization problems and explicitly solved in the case of a two-level system in contact with either bosonic or fermionic thermal environments.
关键词： quantum coherence,bosonic thermal environments,fermionic thermal environments,open quantum system,heat loss minimization,time minimization,two-level system,optimal control
更新于2025-09-23 15:21:01
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Coherent control of spatial and angular Goos-H?¤nchen shifts in a metal-clad waveguide structure
摘要： A metal-clad waveguide backed by a coherent atomic medium is proposed to achieve tunable giant spatial and angular Goos-H?nchen (GH) shifts. With a metal layer of appropriate thickness, a large GH shift can occur simultaneously for transverse-magnetic- and transverse-electric-polarized light beams when the waveguide modes are resonantly excited. The phase change and dip slope of the re?ection coef?cient around the resonance angle are closely related to the system’s internal damping, which depends on the absorption of the medium. Then based on the quantum coherence effect, the spatial and angular shifts can be greatly enhanced by adjusting the parameters of the atomic system. The lateral displacement can also be switched from positive to negative or vice versa via coherent control of the absorption by the medium. Moreover, the dependence of the resonance angle of the guided mode on the refractive index makes the peak position of GH shifts tunable. The proposed scheme provides more ?exibility for manipulating the spatial and the angular GH shifts, and it has potential applications in optical switches, beam steering, etc.
关键词： optical switches,coherent atomic medium,quantum coherence effect,beam steering,Goos-H?nchen shifts,metal-clad waveguide
更新于2025-09-23 15:21:01
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Resonance fluorescence of a single semiconductor quantum dot: the impact of a fluctuating electrostatic environment
摘要： Semiconductor quantum dots are very efficient sources of single and highly indistinguishable photons. These properties rely on the possibility to coherently control the system at the single spin level. At this ultimate level of control, the quantum dot becomes a very sensitive probe of its solid-state environment and any interaction turns into a dephasing process that alters its coherence properties. In this topical review, we give an overview of the issue of charge noise which remains one of the main dephasing mechanisms to overcome. This phenomenon which strongly depends on sample preparation, originates from a fluctuating electrostatic landscape around the quantum dots and renders a unified description quite awkward. We present the common characteristic features induced by charge noise that have been observed in the resonant fluorescence experiments of single quantum dots and discuss the different approaches that have been proposed in the literature to circumvent this problem.
关键词： quantum dots,quantum coherence,optical properties,resonance fluorescence,excitons,III–V semiconductors
更新于2025-09-23 15:19:57
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Verifying multipartite entangled Greenberger-Horne-Zeilinger states via multiple quantum coherences
摘要： The ability to generate and verify multipartite entanglement is an important benchmark for near-term quantum devices. We develop a scalable entanglement metric based on multiple quantum coherences and demonstrate experimentally on a 20-qubit superconducting device. We report a state fidelity of 0.5165 ± 0.0036 for an 18-qubit GHZ state, indicating multipartite entanglement across all 18 qubits. Our entanglement metric is robust to noise and only requires measuring the population in the ground state; it can be readily applied to other quantum devices to verify multipartite entanglement.
关键词： quantum coherence,multipartite entanglement,quantum computing,superconducting qubits,GHZ states
更新于2025-09-23 15:19:57