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Chinese Physics B

Enhancing quantum temporal steering via frequency modulation

Mengkai 孟凯 Wu 吴, Weiwen 维文 Cheng 程

Published Feb 2, 2024• 3 citations
Publisher

Abstract

Various strategies have been proposed to harness and protect space-like quantum correlations in different models under decoherence. However, little attention has been given to temporal-like correlations, such as quantum temporal steering (TS), in this context. In this work, we investigate TS in a frequency-modulated two-level system coupled to a zero-temperature reservoir in both the weak and strong coupling regimes. We analyze the impact of various frequency-modulated parameters on the behavior of TS and non-Markovian. The results demonstrate that appropriate frequency-modulated parameters can enhance the TS of the two-level system, regardless of whether the system is experiencing Markovian or non-Markovian dynamics. Furthermore, a suitable ratio between modulation strength and frequency (i.e., all zeroes of the 0th Bessel function J 0(δ/Ω)) can significantly enhance TS in the strong coupling regime. These findings indicate that efficient and effective manipulation of quantum TS can be achieved through a frequency-modulated approach.

DOI
10.1088/1674-1056/ad2505

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Various strategies have been proposed to harness and protect space-like quantum correlations in different models under decoherence. However, little attention has been given to temporal-like correlations, such as quantum temporal steering (TS), in this context. In this work, we investigate TS in a frequency-modulated two-level system coupled to a zero-temperature reservoir in both the weak and strong coupling regimes. We analyze the impact of various frequency-modulated parameters on the behavior of TS and non-Markovian. The results demonstrate that appropriate frequency-modulated parameters can enhance the TS of the two-level system, regardless of whether the system is experiencing Markovian or non-Markovian dynamics. Furthermore, a suitable ratio between modulation strength and frequency (i.e., all zeroes of the 0th Bessel function J 0(δ/Ω)) can significantly enhance TS in the strong coupling regime. These findings indicate that efficient and effective manipulation of quantum TS can be achieved through a frequency-modulated approach.
Abstract In this paper, the issue of Quantum Synchronization in a driven two‐level (qubit) system situated within a structured environment is examined. The findings have practical implications as it is discovered that adding a time‐dependent periodic modulation to the transition frequency of the qubit can significantly enhance quantum synchronization. The phase preference and, consequently, the phase locking conditions in the system is first discovered using the Husimi ‐function. It is revealed that combining frequency modulation and non‐Markovian effects enables us to achieve a stable phase‐locking for the system. It is shown that tuning the amplitude‐to‐frequency ratio of the modulation process on the zeros of the zeroth‐order Bessel function led to phase locking and, thus, surprisingly enhances quantum synchronization in the system. These results provide new insights into efficiently understanding phase dynamics in quantum environments.
We experimentally simulate a quantum channel in a linear optical setup, which is modeled by a two-level system (i.e., qubit) interacting with a bosonic bath. Unlike the traditional works, we treat the system–bath interaction without applying the Born approximation, the Markov approximation, or the rotating-wave approximation (RWA). To the best of our knowledge, this is the first experimental simulation of a quantum channel without any of the approximations mentioned above by using linear optical devices. This non-RWA channel provides a more accurate picture of the quantum open-system dynamics. It not only reveals the effect of the counterrotating terms but also enables us to consider arbitrarily strong coupling regimes. With the proposed channel, we further experimentally investigate the dynamics of the quantum temporal steering (TS), i.e., a temporal analog of Einstein–Podolsky–Rosen steering. The experimental and theoretical results are in good agreement and show that the counterrotating terms significantly influence the TS dynamics. The TS in non-RWA and RWA channels presents different dynamics. However, we emphasize that the results without RWA are closer to realistic situations and thus more reliable. Due to the close relationship between TS and the security of the quantum cryptographic protocols, our findings are expected to have useful applications in secure quantum communications. This work also inspires future interest in studying other quantum coherence properties in the non-RWA channels.
Controlling the non-Markovian dynamics of open quantum systems is essential in quantum information technology since it plays a crucial role in preserving quantum memory. Albeit in many realistic scenarios the quantum system can simultaneously interact with composite environments, this condition remains little understood, particularly regarding the effect of the coupling between environmental parts. We analyze the non-Markovian behavior of a qubit interacting at the same time with two coupled single-mode cavities which in turn dissipate into memoryless or memory-keeping reservoirs. We show that increasing the control parameter, that is the two-mode coupling, allows for triggering and enhancing a non-Markovian dynamics for the qubit starting from a Markovian one in the absence of coupling. Surprisingly, if the qubit dynamics is non-Markovian for the zero control parameter, increasing the latter enables multiple transitions from non-Markovian to Markovian regimes. These results hold independently on the nature of the reservoirs. This work highlights that suitably engineering the coupling between parts of a compound environment can efficiently harness the quantum memory, stored in a qubit, based on non-Markovianity.
Finding strategies to preserve quantum resources in open systems is nowadays a main requirement for reliable quantum-enhanced technologies. We address this issue by considering structured cavities embedding qubits whose transition frequency is modulated by a driving field. We first focus on a single-qubit system to determine the optimal modulation parameters and the qubit-cavity coupling regime allowing a long-time preservation of both coherence and quantum Fisher information. We relate this behavior to the inhibition of the qubit effective decay rate rather than to stronger memory effects (non-Markovianity) of the system. We then use these findings to efficiently control resources like entanglement, discord and coherence in a system of two separated qubits. We discuss the feasibility of the system and show that individual qubit frequency modulation can produce quantum resource lifetimes orders of magnitude longer than their natural (uncontrolled) decay times. These results provide new useful insights towards efficient experimental strategies against decoherence.
A two-level atom coupled to a reservoir with Lorentzian spectral response function is considered. It is shown that if the free oscillations of the atomic dipole are suitably modulated by an external field, then the dynamics of the spontaneous decay can be strongly modified. As a result, the probability of finding the atom in an excited state can be large even for very long times. This is because the frequency modulation may lead to both effective detuning of the atom from the resonance with reservoir modes and to effective cancellation of the coupling between the atom and the reservoir. Non-Markovian features of the reservoir are found to be essential for this effect to be observable. Conditions of experimental verifications are provided.
Characterizing the dynamics of open systems usually starts with a perturbative theory and involves various approximations, such as the Born, Markov and rotating-wave approximation (RWA). However, the approximation approaches could introduce more or less incompleteness in describing the bath behaviors. Here, we consider a quantum channel, which is modeled by a qubit (a two-level system) interacting with a bosonic bath. Unlike the traditional works, we experimentally simulate the system-bath interaction without applying the Born, Markov, and rotating-wave approximations. To our knowledge, this is the first experimental simulation of the quantum channels without any approximations mentioned above, by using linear optical devices. The results are quite useful and interesting, which not only reveal the effect of the counter-rotating terms but also present a more accurate picture of the quantum channel dynamics. Besides, we experimentally investigate the dynamics of the quantum temporal steering (TS), i.e., a temporal analogue of Einstein-Podolsky-Rosen steering. The experimental and theoretical results are in good agreement and show that the counter-rotating terms significantly influence the TS dynamics. When one monogamously associates TS with the security of the cryptographic protocols (e.g., BB84), our experimental tests reveal that the channels based on RWA will provide exaggerated security durations, while they are actually insecure in non-RWA channel cases. This implies that doing RWA may result in a risk for the security of quantum key distribution. Our findings are expected to have useful applications in secure quantum communications and future interesting TS studies.