Preservation Of Entanglement Research Articles

Preservation of entanglement in local noisy channels

Preservation of entanglement in local noisy channels

Quantum and coherent signal transmission on a single-frequency channel via the electro-optic serrodyne technique.

Fiber-optical networks are well established to accommodate global data traffic via coherent information transmission. The next generation of telecommunications will require the integration of quantum information into fiber-optic networks, e.g., for quantum key distribution. A promising and scalable route to enable quantum networking is encoding quantum information into the frequency of photons. While the cointegration of frequency-entangled photons with coherent information transmission is achieved via spectral multiplexing, more resource-efficient approaches are required. In this work, we introduce and experimentally demonstrate a transceiver concept that enables the transmission of coherent and frequency-entangled photons over a single-frequency channel. Our concept leverages the serrodyne technique via electro-optic phase modulation leading to very different dynamics for entangled and coherent photons. This enables temporal multiplexing of the respective signals. We demonstrate the preservation of entanglement over the channel in the presence of coherent light. Our approach reveals a strong potential for efficient bandwidth use in hybrid networks.

Full Bell-basis measurement of an atom-photon 2-qubit state and its application for quantum networks

The efficiency of a Bell-state measurement on photon pairs is bound to 50% due to the number of Bell states that can be distinguished using linear optics. Here we present the implementation of a protocol that allows us to distinguish all four Bell states by the use of a single-ion quantum memory and heralded absorption as state-selective measurement. The protocol is implemented in two steps. First we demonstrate the state-preserving mapping of a photonic qubit onto the quantum memory, verified by the preservation of entanglement in the process. Then we demonstrate the full Bell-state projection between a memory qubit and an incoming photonic qubit, by applying it for atom-to-photon quantum-state teleportation. Published by the American Physical Society 2024

Gaussian quantum entanglement in curved spacetime

The influence of Hawking radiation on quantum entanglement for bimodal Gaussian states near a Schwarzschild black hole is investigated. It is shown that for a thermal squeezed state of a bimodal bosonic system the Hawking radiation reduces and even can destroy the entanglement between the mode of a Kruskal observer Alice and the mode of Bob, who is an accelerated observer hovering outside the event horizon of black hole. By contrary, the Hawking radiation increases and even can generate quantum entanglement between Bob and anti-Bob, who is a hypothetical observer inside event horizon. We show that in both these scenarios the competition between the contrary influences produced by Hawking temperature, squeezing and field frequency, may favour the preservation of the quantum entanglement. We investigate also the influence of the thermal environment on the behaviour in time of the entanglement between the considered observers and show that the entanglement is destroyed in a finite time for both considered bipartite scenarios of observers Alice and Bob, and respectively Bob and anti-Bob, for non-zero values of the temperature of the thermal environment, i.e. the phenomenon of entanglement sudden death takes place. For a zero temperature of the thermal bath the initial existing entanglement is decreasing over time, but it keeps for all finite times a non-zero value and the logarithmic negativity tends to zero only in the limit of infinite time.

Environment assisted quantum model for studying RNA-DNA-error correlation created due to the base tautomery

The adaptive mutation phenomenon has been drawing the attention of biologists for several decades in evolutionist community. In this study, we propose a quantum mechanical model of adaptive mutation based on the implications of the theory of open quantum systems. We survey a new framework that explain how random point mutations can be stabilized and directed to be adapted with the stresses introduced by the environments according to the microscopic rules dictated by constraints of quantum mechanics. We consider a pair of entangled qubits consist of DNA and mRNA pair, each coupled to a distinct reservoir for analyzing the spreed of entanglement using time-dependent perturbation theory. The reservoirs are physical demonstrations of the cytoplasm and nucleoplasm and surrounding environments of mRNA and DNA, respectively. Our predictions confirm the role of the environmental-assisted quantum progression of adaptive mutations. Computing the concurrence as a measure that determines to what extent the bipartite DNA-mRNA can be correlated through entanglement, is given. Preventing the entanglement loss is crucial for controlling unfavorable point mutations under environmental influences. We explore which physical parameters may affect the preservation of entanglement between DNA and mRNA pair systems, despite the destructive role of interaction with the environments.

Dynamics of quantum-memory assisted entropic uncertainty and entanglement in two-dimensional graphene

We explore the quantum-memory assisted entropic uncertainty (QMA-EU), Jensen-Shannon coherence and entanglement dynamics in a Graphene sheet of disordered electrons in the presence of the intrinsic decoherence. The Graphene sheet containing two sublattices in a two-dimensional honeycomb lattice, which results due to the impurity-potentials interaction of two Dirac points. Entropic uncertainty and logarithmic negativity are used to investigate the generation and preservation of QMA-EU and entanglement under the major factors of Graphene material, including the band structure parameter, the wave numbers as well as the decoherence effect. For the initial uncorrelated two-lattice-point-qubit state, it is found that the lattice-point interactions have high capacity to generated partially/maximally two-lattice-point-qubit entangled and hence the partial/perfect Bob’s ability to guessing the outcome of Alice’s measurement. The increase of the graphite band structure parameter, the wave numbers enhance the generated lattice-point entanglement and Jensen-Shannon coherence, and hence the quantum memory game has a high prediction accuracy. For the intrinsic decoherence, the ability to generate entanglement, Jensen-Shannon coherence. and guessing the Alice’s measurement outcomes weakens. The sudden death-birth phenomenon in the logarithmic-negativity dynamics appears. The increase of the graphite band structure parameter weakens the robustness dynamics against the decoherence effect, while the increase of the wave number operators enhances this robustness. For initial maximally correlated state, the robustness dynamics of the QMA-EU, Jensen-Shannon coherence, and logarithmic-negativity entanglement is very sensitive to the increase of the band structure, wave numbers, and intrinsic decoherence.

Dynamics of quantum-memory assisted entropic uncertainty of a two-spin Heisenberg XXX model under the intrinsic decoherence effect

In this study, the quantum-memory assisted entropic uncertainty (QM-EU) and entanglement dynamics of the two-qubit Heisenberg XXX chain have been explored in the presence of intrinsic decoherence. The effect of the x-component of Dzyaloshinskii-Moriya (DM) and Kaplan-Shekhtman-Entin-Wohlman-Aharony (KSEA) interactions has been considered. The generation and preservation of quantum memory and entanglement have been examined for various values of the DM, KSEA, spin-spin, and spin coupling strengths. The uncertainty negatively affects the entanglement and both have anti-correlation. The absence and presence of intrinsic decoherence prevail in differing impacts on the dynamics of the system. In the first case, prolonged entanglement preservation, uncertainty suppression, and oscillatory dynamics have been observed. Moreover, in order to achieve the best-prolonged entanglement preservation and relative reduction of the entropic uncertainty, we have analyzed several parameter settings. We find that the effects of raising the DM, KSEA, and spin-spin interaction individually and simultaneously are different. The individual and simultaneous increase of the DM, KSEA, and spin-spin interaction parameters control the degree of entanglement, entropic uncertainty, and primarily the dynamics of the system.

Telecom quantum photonic interface for a 40Ca+ single-ion quantum memory

Entanglement-based quantum networks require quantum photonic interfaces between stationary quantum memories and photons, enabling entanglement distribution. Here we present such a photonic interface, designed for connecting a 40Ca+ single-ion quantum memory to the telecom C-band. The interface combines a memory-resonant, cavity-enhanced spontaneous parametric down-conversion photon pair source with bi-directional polarization-conserving quantum frequency conversion. We demonstrate preservation of high-fidelity entanglement during conversion, fiber transmission over up to 40 km and back-conversion to the memory wavelength. Even for the longest distance and bi-directional conversion the entanglement fidelity remains larger than 95% (98%) without (with) background correction.

Entanglement mediated by DC current induced nonreciprocal graphene plasmonics.

We investigate entanglement mediated by DC current induced nonreciprocal graphene plasmon polaritons. Nonreciprocal systems are ideal for the enhancement, control, and preservation of entanglement due to the potential for unidirectional beam-like wave propagation, i.e., efficiently transporting photons from one emitter to another. Using a quantum master equation and three-dimensional Green's function analysis, we investigate a system consisting of two two-level emitters dominantly interacting via electric current induced nonreciprocal plasmonic modes of a graphene waveguide. We use concurrence as a measure of entanglement. We show that nonreciprocal graphene plasmon polaritons are a promising candidate to generate and mediate concurrence, where it is shown that there is good enhancement and control of entanglement over vacuum, which is beneficial for the broad applications of entanglement as a quantum resource. We believe our findings contribute to the development of quantum devices, enabling efficient and tunable entanglement between two-level systems, which is a central goal in quantum technologies.

Sharing entanglement of the Werner state by arbitrarily many independent observers

The problem of sharing quantum correlations is an interesting problem in the study of quantum information theory. Silva et al. proposed the study of sharing quantum nonlocality at first. They studied the fundamental limits on nonlocality, asking whether a single pair of entangled qubits could generate a long sequence of nonlocal correlations. At the same time, the sequential scenario was also introduced first, in which Alice and Bob each have half of a pair of entangled qubit states. The first Bob measures his half and then passes his part to a second Bob who measures again and so on. Obviously, even partial preservation of entanglement in a shared state in spite of a few sequences of local operations performed by the sharing parties can be important for information processing schemes in which entanglement is utilized as a resource. Thus, the problem of sharing quantum entanglement has also been extensively investigated. Recently, Srivastava et al. proved that there exist a class of T-states whose entanglement can be shared by arbitrarily many independent observers in [<ext-link ext-link-type="uri" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://doi.org/10.1103/PhysRevA.105.062413"><i>Phys. Rev. A</i> 2022 <b>105</b> 062413</ext-link>]. Here, we want to find whether there are other entangled states that can be shared entanglement arbitrarily many times. In this paper, we consider the problem of sharing quantum entanglement when the initial shared state is a two-qubit entangled Werner state. The goal is to maximize the number of Bobs that can share entanglement with a single Alice. By suitably choosing the entanglement witness operator and the unsharp measurement settings by the Bobs, we prove that there exist two-qubit entangled initial shared Werner states whose entanglement can be detected by arbitrarily many sequential observers Bobs with a single Alice. Then, we also consider the special case of the Werner state, that is, the maximally entangled state as the initial shared state. In this case, its entanglement can also be witnessed arbitrarily many times, and the number of Bobs increases with the decrease of parameter.

Multipartite entanglement and purity dynamics in channels influenced by fractional Gaussian noise

The dynamical map of entanglement, coherence and mixedness in four-qubit maximally entangled GHZ-class state paired with classical channels driven by fractional Gaussian noise is investigated. The qubit-channel coupling is assumed in four distinct ways: common, bipartite, tripartite, and independent local channel-qubit configurations comprising single, double, triple, or independent noisy sources. Using entanglement witness, negativity, purity and von Neumann entropy, except for the independent configuration, we show that indefinite entanglement, coherence, and purity preservation may be simulated in multipartite GHZ-like states. Quantum correlations and purity decrease exponentially in four qubits, and exact fluctuating local field behavior, as well as entanglement sudden death and birth revivals, are completely suppressed. Entanglement, coherence, and purity preservation are affected by noise and the number of independent channels utilized. The Hurst parameter of fractional Gaussian noise was discovered in the four qubits to improve entanglement, coherence and avoid mixedness.

Long-time protection of thermal correlations in a hybrid-spin system under random telegraph noise.

The engineering features of transmitting mediums and their impact on different characteristics of a quantum system play a significant role in the efficient performance of nonlocal protocols. For this purpose, the dynamics of open quantum systems and coupling mediums remain a pathway. In this work, we investigate the dynamics of quantum correlations using negativity, uncertainty-induced nonlocality, and local quantum Fisher information in a hybrid qubit-qutrit thermal state when coupled with a magnetic field and influenced by random telegraph noise. Different features of the system parameters are taken into account while designing longer preservation of qubit-qutrit correlations. We show that the temperature has an inverse impact on the initial values of negativity, uncertainty-induced nonlocality, and local quantum Fisher information. When the magnetic field is characterized by different features, the entanglement, nonlocality, and Fisher information show a variety of dynamical maps, assuring their distinct nature. In addition, the qubit-qutrit correlations undergo repeated revivals when the configuration is restricted to the non-Markovian regime. On the other hand, an exponential drop with a single minimum is observed in the Markovian regime of the coupled field. Most importantly, our findings reveal that the present coupled fields have several advantages that can be leveraged to generate the optimal degree of entanglement, nonlocality, and local quantum Fisher information preservation in quantum dynamical maps.

Protecting quantum coherence and entanglement in a correlated environment

Long-term preservation of quantum coherence and entanglement is indispensable for practical quantum computation. We study the evolution of quantum coherence and genuine multipartite concurrence of extended Werner like states transmitted through correlated amplitude damping (AD), phase damping (PD) and depolarizing (DP) channels. The results show that the decay rate of coherence is curtailed in the presence of correlation between successive actions of the channel. It is shown that the fragility of genuine multipartite entanglement due to decoherence can be protected to some significant amount by using the correlated channels. In fact, for even qubit Werner like states, coherence and entanglement exhibit freezing phenomenon, in which it remains intact against decohering environment in perfectly correlated phase damping and depolarizing channels. For multipartite GHZ-class states in a perfectly correlated channel, it is shown that entanglement sudden death (ESD) is circumvented in amplitude damping channel, and there is an entanglement sudden birth (ESB) for odd qubit systems in depolarizing channel. Further, we have established analytical relation between coherence and entanglement for completely uncorrelated and fully correlated quantum channels.

Direct measurement of nonlocal interactions in the many-body localized phase

The interplay of interactions and strong disorder can lead to an exotic quantum many-body localized (MBL) phase of matter. Beyond the absence of transport, the MBL phase has distinctive signatures, such as slow dephasing and logarithmic entanglement growth; they commonly result in slow and subtle modifications of the dynamics, rendering their measurement challenging. Here, we experimentally characterize these properties of the MBL phase in a system of coupled superconducting qubits. By implementing phase sensitive techniques, we map out the structure of local integrals of motion in the MBL phase. Tomographic reconstruction of single and two-qubit density matrices allows us to determine the spatial and temporal entanglement growth between the localized sites. In addition, we study the preservation of entanglement in the MBL phase. The interferometric protocols implemented here detect affirmative quantum correlations and exclude artifacts due to the imperfect isolation of the system. By measuring elusive MBL quantities, our work highlights the advantages of phase sensitive measurements in studying novel phases of matter.Received 30 March 2021Accepted 10 November 2021DOI:https://doi.org/10.1103/PhysRevResearch.4.013148Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasLocalizationMany-body localizationQuantum entanglementQuantum simulationPhysical SystemsSuperconducting qubitsCondensed Matter, Materials & Applied PhysicsQuantum Information

Probing tripartite entanglement and coherence dynamics in pure and mixed independent classical environments

The type of environments to which a quantum system is exposed has a significant impact on the quantum system’s entanglement and coherence protection. In this regard, we investigate the time evolution of tripartite entanglement and coherence in GHZ-like state when subject to independent classical environments. In particular, we focus on local environments with the same and mixed disorders, resulting in various Gaussian noisy conditions, namely pure power-law noise, pure fractional Gaussian noise, power-law noise maximized, and fractional Gaussian noise maximized configurations. We show that the environments with mixed disorders are more detrimental than those having single kind of disorder for entanglement and coherence preservation using time-dependent quantum negativity, entanglement witnesses, purity, and decoherence metrics. Besides, there is no ultimate solution for avoiding the negative consequences of fractional Gaussian noise-assisted classical environments in both pure and mixed noise conditions. Not only the noise, but also the number of qubits driven by a certain noise, has been discovered to strongly influence the amount, nature of the decay, and preservation intervals. We also show that the GHZ-like states can be modelled in classical channels driven by pure power-law noise for extended quantum correlations, coherence, and quantum information preservation. In addition, we compare the entanglement measurement efficiency between entanglement witness and negativity measures.

Quantifying entanglement preservability of experimental processes

Preserving entanglement is a crucial dynamical process for entanglement-based quantum computation and quantum-information processes, such as one-way quantum computing and quantum key distribution. However, the problem of quantifying the ability of an experimental process to preserve two-qubit entanglement in experimentally feasible ways is not well understood. Accordingly, herein, we consider the use of two measures, namely composition and robustness, for quantitatively characterizing the ability of a process to preserve entanglement, referred to henceforth as entanglement preservability. A fidelity benchmark is additionally derived to identify the ability of a process to preserve entanglement. We show that the measures and introduced benchmark are experimentally feasible and require only local measurements on single qubits and preparations of separable states. Moreover, they are applicable to all physical processes that can be described using the general theory of quantum operations, e.g., qubit dynamics in photonic and superconducting systems. Our method extends the existing tools for analyzing channels, e.g., channel resource theory, to quantify entanglement preservability for non-trace-preserving quantum processes. The results are of significant interest for applications in quantum-information processing in which entanglement preservation is required.

Resource theory of unextendibility and nonasymptotic quantum capacity

In this paper, we introduce the resource theory of unextendibility as a relaxation of the resource theory of entanglement. The free states in this resource theory are the k-extendible states, associated with the inability to extend quantum entanglement in a given quantum state to multiple parties. The free channels are k-extendible channels, which preserve the class of k-extendible states. We define several quantifiers of unextendibility by means of generalized divergences and establish their properties. By utilizing this resource theory, we obtain non-asymptotic upper bounds on the rate at which quantum communication or entanglement preservation is possible over a finite number of uses of an arbitrary quantum channel assisted by k-extendible channels at no cost. These bounds are significantly tighter than previously known bounds for both the depolarizing and erasure channels. Finally, we revisit the pretty strong converse for the quantum capacity of antidegradable channels and establish an upper bound on the non-asymptotic quantum capacity of these channels.

Witnessing the survival of time-energy entanglement through biological tissue and scattering media.

We demonstrate the preservation of the time-energy entanglement of near-IR photons through thick biological media (≤1.55 mm) and tissue (≤ 235 μm) at room temperature. Using a Franson-type interferometer, we demonstrate interferometric contrast of over 0.9 in skim milk, 2% milk, and chicken tissue. This work supports the many proposed opportunities for nonclassical light in biological imaging and analyses from sub-shot noise measurements to entanglement-enhanced fluorescence imaging, clearly indicating that the entanglement characteristics of photons can be maintained even after propagation through thick, turbid biological samples.

Quantumness Measures for a System of Two Qubits Interacting with a Field in the Presence of the Time-Dependent Interaction and Kerr Medium.

In this work, we introduce the standard Tavis-Cummings model to describe two-qubit system interacting with a single-mode field associated to power-law (PL) potentials. We explore the effect of the time-dependent interaction and the Kerr-like medium. We solve the Schrödinger equation to obtain the density operator that allows us to investigate the dynamical behaviour of some quantumness measures, such as von Neumann entropy, negativity and Mandel’s parameter. We provide how these entanglement measures depend on the system parameters, which paves the way towards better control of entanglement generation in two-qubit systems. We find that the enhancement and preservation of the atoms-field entanglement and atom-atom entanglement can be achieved by a proper choice of the initial parameters of the field in the absence and presence of the time-dependent interaction and Kerr medium. We examine the photons distribution of the field and determine the situations for which the field exhibits super-poissonian, poissonian or sub-poissonian distribution.

Entanglement-preserving limit cycles from sequential quantum measurements and feedback

Entanglement generation and preservation is a key task in quantum information processing, and a variety of protocols exist to entangle remote qubits via measurement of their spontaneous emission. We here propose feedback methods, based on monitoring the fluorescence of two qubits and using only local pi-pulses for control, to increase the yield and/or lifetime of entangled two-qubit states. Specifically, we describe a protocol based on photodetection of spontaneous emission (i.e. using quantum jump trajectories) which allows for entanglement preservation via measurement undoing, creating a limit cycle around a Bell states. We then demonstrate that a similar modification can be made to a recent feedback scheme based on homodyne measurement (i.e. using diffusive quantum trajectories), [L. S. Martin and K. B. Whaley, arXiv:1912.00067] in order to increase the lifetime of the entanglement it creates. Our schemes are most effective for high measurement efficiencies, and the impact of less-than-ideal measurement efficiency is quantified. The method we describe here combines proven techniques in a novel way, complementing existing protocols, and offering a pathway towards generating and protecting entangled states so that they may be used in various applications on demand.