1,721,033 research outputs found
Directly proving the bosonic nature of photons
No full textA simple yet effective optical set-up, employing two controllable, indistinguishable photons, is proven to allow a direct measurement of the exchange phase due to the bosonic particle statistics
Entanglement and coherence dynamics in photonic quantum memristors
Full text linkMemristive systems exhibit dynamics that depend on their past states, making them useful as memory units. Recently, quantum memristor models have been proposed, and notably, a photonic quantum memristor (PQM) has been experimentally proven. In this work, we explore and characterize various quantum properties that emerge from this specific model of PQM. First, we find that a single PQM displays memristive dynamics on its quantum coherence. Second, we analytically show that a network made of two independent PQMs can manifest memory effects on the dynamics of both entanglement and coherence of correlated photons traveling through the network, regardless of their distance, in the hypothesis of negligible external disturbances. Additionally, we build and run a circuit-model of the PQM on a real qubit-based quantum computer (IBM-Q), showing that (1) this system can effectively be used for nonlinear quantum computing under specific conditions and (2) digital quantum simulations can reproduce the dynamics of a memristive quantum system in a non-Markovian regime
Searching for exceptional points and inspecting non-contractivity of trace distance in (anti-) PT -symmetric systems
Full text linkNon-Hermitian systems with parity-time (PT) symmetry and anti-PT symmetry lead to exceptional points (EPs) with intriguing properties related to, e.g., chiral transport and enhanced sensitivity, due to the coalescence of eigenvectors. In this paper, we propose an easily computable tool, based on the Hilbert–Schmidt speed (HSS), not requiring the diagonalization of the evolved density matrix, to detect exactly the EPs, especially in high-dimensional systems. Our theoretical predictions, made without the need for modification of the Hilbert space, are completely consistent with results extracted from recent experiments studying the criticality in (anti-)PT-symmetric systems. Moreover, not modifying the Hilbert space of the non-Hermitian system, we find that the trace distance whose dynamics is known as a faithful witness of non-Markovianity, may be non-contractive under the non-Hermitian evolution of the system. Therefore, it losses one of the most important characteristics which must be met by any standard witness of non-Markovianity. We also address the non-contractivity of quantum Fisher information in non-Hermitian systems
Hilbert–Schmidt speed as an efficient figure of merit for quantum estimation of phase encoded into the initial state of open n-qubit systems
Full text linkHilbert–Schmidt speed (HSS) is a special type of quantum statistical speed which is easily computable, since it does not require diagonalization of the system state. We find that, when both HSS and quantum Fisher information (QFI) are calculated with respect to the phase parameter encoded into the initial state of an n-qubit register, the zeros of the HSS dynamics are actually equal to those of the QFI dynamics. Moreover, the signs of the time-derivatives of both HSS and QFI exactly coincide. These findings, obtained via a thorough investigation of several paradigmatic open quantum systems, show that HSS and QFI exhibit the same qualitative time evolution. Therefore, HSS reveals itself as a powerful figure of merit for enhancing quantum phase estimation in an open quantum system made of n qubits. Our results also provide strong evidence for both contractivity of the HSS under memoryless dynamics and its sensitivity to system-environment information backflows to detect the non-Markovianity in high-dimensional systems, as suggested in previous studies
Quantumness and memory of one qubit in a dissipative cavity under classical control
Full text linkHybrid quantum–classical systems constitute a promising architecture for useful control strategies of quantum systems by means of a classical device. Here we provide a comprehensive study of the dynamics of various manifestations of quantumness with memory effects, identified by non-Markovianity, for a qubit controlled by a classical field and embedded in a leaky cavity. We consider both Leggett–Garg inequality and quantum witness as experimentally-friendly indicators of quantumness, also studying the geometric phase of the evolved (noisy) quantum state. We show that, under resonant qubit-classical field interaction, a stronger coupling to the classical control leads to enhancement of quantumness despite a disappearance of non-Markovianity. Differently, increasing the qubit-field detuning (out-of-resonance) reduces the nonclassical behavior of the qubit while recovering non-Markovian features. We then find that the qubit geometric phase can be remarkably preserved irrespective of the cavity spectral width via strong coupling to the classical field. The controllable interaction with the classical field inhibits the effective time-dependent decay rate of the open qubit. These results supply practical insights towards a classical harnessing of quantum properties in a quantum information scenari
Witnessing global memory effects of multiqubit correlated noisy channels by Hilbert-Schmidt speed
No full textIn correlated noisy channels, the global memory effects on the dynamics of a quantum system depend on both non-Markovianity of the single noisy channel (intrinsic memory) and classical correlations between multiple uses of the channel itself (correlation-based memory). We show that the Hilbert-Schmidt speed (HSS), a measure of non-Markovianity, serves as a reliable figure of merit for evaluating the role of this correlation-based memory on the global memory effects, for both unital and non-unital channels irrespective of initial basis. The intensity of the correlation-based memory is ruled by a classical correlation strength between consecutive applications of the channel. We establish that classical correlation between multiple uses of a channel does not alter the duration of revivals in unital channels, whereas in non-unital channels, it does. Therefore, HSS can serve as an effective tool for distinguishing between unital and non-unital correlated channels. We demonstrate that, for unital noisy channels, increasing the number of qubits of the system significantly weakens the sensitivity of the HSS to this classical correlation strength. Such a pattern indicates that the state evolution of large quantum systems may be less prone to be affected by classical correlations between noisy channels. Moreover, assuming that the qubits are affected by independent or classically correlated local non-Markovian unital channels, we observe that, as the number of qubits increases, the collective behavior of the multiqubit system inhibits the non-Markovian features of the overall system dynamics
Dynamics of spatially indistinguishable particles and quantum entanglement protection
No full textA complete treatment of open quantum systems made of identical particles has remained elusive due to the intrinsic problem of these particles being individually unaddressable. Filling this gap is essential for the full characterization of quantum networks which are typically built by identical subsystems. We provide a general framework which allows one to obtain the dynamics of N noninteracting spatially indistinguishable particles locally coupled to separated environments. This framework is universal, being valid for both bosons and fermions and for any type of system-environment interaction. It is applied to study the dynamics of two identical qubits under paradigmatic Markovian noises, such as phase damping, depolarization, and amplitude damping. We find that spatial indistinguishability of identical qubits is a controllable inherent property of the system which protects exploitable quantum entanglement against detrimental noise
Relativistic quantum thermometry through a moving sensor
Full text linkUsing a two-level moving probe, we address the temperature estimation of a static thermal bath modeled by a massless scalar field prepared in a thermal state. Different couplings of the probe to the field are discussed under various scenarios. We find that the thermometry is completely unaffected by the Lamb shift of the energy levels. We take into account the roles of probe velocity, its initial preparation, and environmental control parameters for achieving optimal temperature estimation. We show that a practical technique can be utilized to implement such a quantum thermometry. Finally, exploiting the thermal sensor moving at high velocity to probe temperature within a multiparameter-estimation strategy, we demonstrate perfect supremacy of the joint estimation over the individual one
Witnessing non-Markovian effects of quantum processes through Hilbert-Schmidt speed
Full text linkNon-Markovian effects can speed up the dynamics of quantum systems while the limits of the evolution time can be derived by quantifiers of quantum statistical speed. We introduce a witness for characterizing the non-Markovianity of quantum evolutions through the Hilbert-Schmidt speed (HSS), which is a special type of quantum statistical speed. This witness has the advantage of not requiring diagonalization of the evolved density matrix. Its sensitivity is investigated by considering several paradigmatic instances of open quantum systems, such as one qubit subject to phase-covariant noise and a Pauli channel, two independent qubits locally interacting with leaky cavities, and V-type and Lambda-type three-level atoms (qutrits) in a dissipative cavity. We show that the proposed HSS-based non-Markovianity witness detects memory effects, in agreement with the well-established trace-distance-based witness, being sensitive to system-environment information backflows
Indistinguishability-Enhanced Entanglement Recovery by Spatially Localized Operations and Classical Communication
Full text linkWe extend a procedure exploiting spatial indistinguishability of identical particles to recover the spoiled entanglement between two qubits interacting with Markovian noisy environments. Here, the spatially localized operations and classical communication (sLOCC) operational framework is used to activate the entanglement restoration from the indistinguishable constituents. We consider the realistic scenario where noise acts for the whole duration of the process. Three standard types of noises are considered: a phase damping, a depolarizing, and an amplitude damping channel. Within this general scenario, we find the entanglement to be restored in an amount proportional to the degree of spatial indistinguishability. These results elevate sLOCC to a practical framework for accessing and utilizing quantum state protection within a quantum network of spatially indistinguishable subsystems
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