Measurement-induced Disturbance Research Articles

Witnessing quantum correlations in two coupled quantum dots under intrinsic decoherence

The influences of intrinsic decoherence, tunnelling rates, and Coulomb coupling interaction on the behaviour of negativity, quantum coherence and the measurement-induced disturbance of two coupled quantum dot molecules are discussed. The aforementioned is implemented by obtaining the exact solution of the Milburn equation, where the initial setting state is prepared in an entangled Werner state. Various phenomena are illustrated for three physical measures, namely entanglement, coherence, and quantum correlations. It showed that the intrinsic decoherence strength plays a destructive role for the maximum bounds of all these physical quantities, in which they are decayed to a non-zero fixed point. Altering the tunnelling rates strength increases/ decreases the maximum and minimum bounds of the three physical measurements, whereby increasing the tunnelling rate lessens the entanglement and denigrates the maximum and minimum values of coherence and quantumness. Otherwise, the Coulomb coupling enhances the stability of all physical quantities.

Quantum Correlation Swapping between Two Werner States Undergoing Local and Nonlocal Unitary Operations.

In this paper, quantum correlation (QC) swapping between two Werner-like states, which are transformed from Werner states undergoing local and nonlocal unitary operations, are studied. Bell states measures are performed in the middle node to realize the QC swapping and correspondingly final correlated sates are obtained. Two different QC quantifiers, i.e., measurement-induced disturbance (MID) and ameliorated MID, are employed to characterize and quantify all the concerned QCs in the swapping process. All QCs in the concerned states are evaluated analytically and numerically. Correspondingly, their characteristics and properties are exposed in detail. It is exposed that, through the QC swapping process, one can obtain the long-distance QC indeed. Moreover, the similarities of monotony features of MID and AMID between the initial states and final states are exposed and analyzed.

Increasing Quantum Correlations Based on Measurement-Induced Disturbance via a Swapping Procedure with Two-Qubit Mixed States.

In this paper, quantum correlation (QC) swapping for certain separable two-qubit mixed states is treated. A QC quantifier, measurement-induced disturbance (MID) (Luo in Phys Rev A 77:022301, 2008), is employed to characterize and quantify QCs in the relevant states. Properties of all QCs in the swapping process are revealed. Particularly, it is found that MID can be increased through QC swapping for certain separable two-qubit mixed states.

Decoherence in two-dimensional quantum walks with two- and four-state coins

Two-dimensional quantum walks using a two-state coin have simpler experimental implementation than two-dimensional quantum walks using a four-state coin. However, decoherence occurs inevitably during the evolution of quantum walks due to the coupling between the quantum systems and their environment. Thus, it is interesting to investigate the robustness against decoherence for two- and four-state two-dimensional quantum walks. Here, we investigate the effects of the decoherence on two- and four-state two-dimensional quantum walks produced by the broken-link-type noise and compare their robustness against the broken-link-type noise. Specifically, we analyze the quantum correlation between the two spatial dimensions x and y by using measurement-induced disturbance for the two-state quantum walks, i.e. the alternate walk and the Pauli walk, and the four-state quantum walks, i.e. the Grover, Hadamard and Fourier walks, respectively. Our analysis shows that the two-state walks are more robust against the broken-link-type noise than the four-state walks.

Steering-induced coherence in decoherence channels

We study steering-induced coherence (SIC) in local decoherence channels. Two types of channels are considered in this work, one is the amplitude damping channel under rotating-wave approximation (RWA) and the other the non-RWA channel. Unlike the amplitude damping channel, the system-environment interaction of the non-RWA channel is treated without RWA. We use the hierarchy equation method to calculate the dynamical evolution of SIC and B-side measurement-induced disturbance (MID). For the two channels, SIC decreases with time monotonically or oscillatingly due to the decoherence effect. Moreover, the different behavior of SIC between the two channels are also shown through the numerical results. SIC and MID obviously exhibit more oscillatory behavior in the non-RWA channel compared with the cases in the RWA channel. In some regions of system-environment coupling, the value of SIC (MID) in the non-RWA channel is larger than that in the RWA channel. However, in the strong non-Markovian regions, SIC (MID) drops to zero in the RWA channel, while it does not happen in the non-RWA channels. Additionally, we find that SIC can be generated from the states without entanglement.

Quantum correlation swapping between Werner and separable states

In this paper we study quantum correlation (QC) swapping between two different kinds of quantum-correlated states. To be concrete, one is the famous Werner state while another is a kind of separable state. We employ measurement-induced disturbance (Luo 2008 Phys. Rev. A 77 02230) as the quantifier to characterize and quantify QC. We work out QCs in all the concerned states and concretely analyze their behaviors and properties such monotony features and thresholds. We find that a long-distance shared QC can be generated from two short-distance ones via intermediate measure. Moreover, the amount of the long-distance shared QC cannot reach that in the Werner state but that in the separable state.

Observing the quantum Cheshire cat effect with noninvasive weak measurement

One of the common conceptions of nature, typically derived from the experiences with classical systems, is that attributes of the matter coexist with the substance. In the quantum regime, however, the quantum particle itself and its physical property may be in spatial separation, known as the quantum Cheshire cat effect. While there have been several reports to date on the observation of the quantum Cheshire cat effect, all such experiments are based on first-order interferometry and destructive projection measurement, thus allowing simple interpretation due to measurement-induced disturbance and also subject to trivial interpretation based on classical waves. In this work, we report an experimental observation of the quantum Cheshire cat effect with noninvasive weak quantum measurement as originally proposed. The use of the weak-measurement probe has allowed us to identify the location of the single photon and that of the disembodied polarization state in a quantum interferometer. The weak-measurement probe based on two-photon interference makes our observation unable to be explained by classical physics. We furthermore elucidate the quantum Cheshire cat effect as quantum interference of the transition amplitudes for the photon and the polarization state which are directly obtained from the measurement outcomes or the weak values. Our work not only reveals the true quantum nature of Cheshire cat effect but also sheds light on a comprehensive understanding for the counter-intuitive quantum phenomena.

Dynamics of quantum discord based on linear entropy and negativity of qutrit-qubit system under classical dephasing environments

A reliable analytical method to evaluate the non-classical correlations based on linear entropy for an arbitrary qudit-qubit quantum state is proposed. The linear entropy is used to overcome the difficulty encountered with the computability of quantum discord based on von Neumann entropy. The quantum discord based on linear entropy is employed to derive the quantum correlations for a qutrit-qubit system undergoing global (bilocal + collective) classical dephasing environment. Our studies were focused mainly on a particular initial qutrit-qubit state in thermal equilibrium at a temperature T. The obtained amount of quantum discord (QD) is then compared with the measurement-induced disturbance (MID) and logarithmic negativity (LN). The analysis shows that both QD and MID are more robust than entanglement (LN) against the decoherence effect. Besides, the system exhibits interesting behaviors. As for instance, freezing dynamics and entanglement sudden death (ESD). The method developed in this paper to quantify quantum correlations is reliable because it allows us to consider analytically the arbitrary qutrit-qubit quantum states in the classical dephasing environment.

A two-dimensional quantum walk driven by a single two-side coin* *Project supported by the National Natural Science Foundation of China (Grant Nos. 11674056 and U1930402) and the startup fund from Beijing Computational Science Research Center. KKW acknowledges support from the Project funded by China Postdoctoral Science Foundation (Grant No. 2019M660016).

We study a two-dimensional quantum walk with only one walker alternatively walking along the horizontal and vertical directions driven by a single two-side coin. We find the analytical expressions of the first two moments of the walker’s position distribution in the long-time limit, which indicates that the variance of the position distribution grows quadratically with walking steps, showing a ballistic spreading typically for quantum walks. Besides, we analyze the correlation by calculating the quantum mutual information and the measurement-induced disturbance respectively as the outcome of the walk in one dimension is correlated to the other with the coin as a bridge. It is shown that the quantum correlation between walker spaces increases gradually with the walking steps.

Quantum discord based on linear entropy and thermal negativity of qutrit–qubit mixed spin chain under the influence of external magnetic field

We propose a reliable analytical method to evaluate the non-classical correlations based on linear entropy for an arbitrary qudit–qubit quantum state. The linear entropy is used to overcome the difficulty of the maximization of the classical correlations encountered when the von Neumann entropy is used in determining quantum discord. The quantum discord based on linear entropy is employed to derive the amount of quantum correlations in a qutrit–qubit mixed spin system in the thermal equilibrium at temperature T. We investigate also the situation when the system is embedded in an external magnetic field. The obtained amount of quantum discord is then compared with the measurement-induced disturbance (MID) and logarithmic negativity. The analysis shows that both QD and MID are more robust than entanglement. Besides, QD and MID can be exploited to determine the critical points of quantum phase transitions in the system.

New properties of a pure bipartite system in presence of dissipative environments

We investigate some new properties of the model of a pure bipartite system in dissipative environments. The mathematical model of bipartite system with the interaction cavity field in the presence of dissipative environment is designed. The systems is assumed to be initially in the Warner state. The system is analytically solved using master equation method. We quantified the dynamics of quantum correlation between the system, under the influence of the mean photon numbers, type of the initial state and spontaneous emission rate of atom using several measures are, measurement-induced disturbance (MID) and Geometric measure of quantum discord (GQD), negativity (N) and concurrence (C). The effect of the system parameters on dynamics of entanglement is investigated, it is found that the spontaneous emission rate of atom number have much effect on all measures. Moreover the Geometric measure of quantum discord (GQD) have different behavior rather than the others and more influenced by the mean photon number and type of the initial state.

Two Quantum Coins Sharing a Walker

For classical random walks, changing or not changing coins makes a trivial influence on the random-walk behaviors. In this paper, we investigate the quantum walk where a walker’s movement is controlled by two initially independent coins alternately partially or fully after each step. We observe that there exist complicated inter-coin correlations in the quantum walk. Specifically, we study the correlations of two coins by tracing out the walker, and analyze classical, general, and quantum correlations between two coins in terms of classical mutual information, quantum mutual information, and measurement-induced disturbance. Our analysis shows different quantum features from that in classical random walks.

The dynamics of tripartite quantum correlations under Ornstein–Uhlenbeck noise

The dynamics of the tripartite thermal entanglement measured by Negativity (N) and the tripartite quantum correlation described by measurement-induced disturbance (MID) under Ornstein–Uhlenbeck noise are investigated. This study has found that the tripartite N and MID can be preserved more effectively in the non-Markovian environment than in the short-time limit and the Markov limit cases. The short-time limit is a better approximation than the Markov limit. MID vanishes only in the asymptotic limit, while entanglement sudden death may occur, and the decreasing duration of MID far outweighs entanglement. This implies that MID is more robust than Negativity. As the noise bandwidth increases, the disentanglement time and the decay time of MID are significantly shorter. The increase of XZX[Formula: see text]+[Formula: see text]YZY three-site interaction is more effective than XZY−YZX three-site interaction to enhance Negativity and MID as well as the disentanglement time. The magnetic field diminishes Negativity and MID, but has no significant influence on the decreasing durations of both Negativity and MID.

Quantum phase transition for the XY chain with Dzyaloshinsky–Moriya interaction

We study quantum phase transition of the [Formula: see text] spin model with Dzyaloshinsky–Moriya interaction, by using quantum correlation measures, i.e. quantum deficit and measurement-induced disturbance. It is shown that as the Dzyaloshinsky–Moriya coupling parameter [Formula: see text] increases, the behaviors of quantum phase transition can be suppressed. We also investigate quantum phase transition for the Ising and [Formula: see text] spin models at finite temperature. It is found that quantum phase transition characterized by measurement-induced disturbance is greater than or equal to that characterized by quantum deficit. Other interesting analytical results and numerical results on quantum phase transition for the proposed spin models are also presented by applying the two measures. Furthermore, we also compare quantum deficit and measurement-induced disturbance with quantum entanglement, quantum discord and quantum coherence.

Experimental investigation of measurement-induced disturbance and time symmetry in quantum physics

Unlike regular time evolution governed by the Schr\"odinger equation, standard quantum measurement appears to violate time-reversal symmetry. Measurement creates random disturbances (e.g., collapse) that prevents back-tracing the quantum state of the system. The effect of these disturbances is explicit in the results of subsequent measurements. In this way, the joint result of sequences of measurements depends on the order in time in which those measurements are performed. One might expect that if the disturbance could be eliminated this time-ordering dependence would vanish. Following a recent theoretical proposal [A. Bednorz et al 2013 New J. Phys. 15 023043], we experimentally investigate this dependence for a kind of measurement that creates an arbitrarily small disturbance, weak measurement. We perform various sequences of a set of polarization weak measurements on photons. We experimentally demonstrate that, although the weak measurements are minimally disturbing, their time-ordering affects the outcome of the measurement sequence for quantum systems.

Total-Ionizing-Dose Response of Nb2O5-Based MIM Diodes for Neuromorphic Computing Applications

Nb2O5-based metal–insulator–metal (MIM) diodes are ideal for neuromorphic computing applications because they exhibit desirable rectification, hysteresis, and capacitance characteristics without electroforming. We employ capacitance-frequency measurements to evaluate the total-ionizing-dose res- ponse of these devices to avoid measurement-induced disturbance of trap distributions caused by typical gate-voltage sweeping methods. Power-law dependences are observed for the low-frequency capacitance and conductance, consistent with hopping conduction of carriers through the oxides. Despite their high oxygen-vacancy densities, the Nb2O5-based MIM diodes are radiation tolerant up to at least Mrad(SiO2) doses.

Tripartite and bipartite quantum correlations in the XXZ spin chain with three-site interaction

Tripartite and bipartite quantum correlations in the three-qubit XXZ Heisenberg spin chain with two types of three-site interactions and an external magnetic field are investigated. We show that the increase in XZY − YZX interaction can enhance the robustness of both tripartite and bipartite correlations, whereas the increase in XZX $$+$$ YZY interaction could improve the robustness of tripartite quantum correlations, but diminish the robustness of bipartite quantum correlations. Tripartite measurement-induced disturbance is the most robust against temperature, and bipartite entanglement is the most fragile. Tripartite entanglement is even more robust than bipartite quantum discord when XZX $$+$$ YZY or XZY − YZX interaction is relatively large. The cooperative effect of XZX $$+$$ YZY and XZY − YZX interaction could induce bipartite entanglement even at high temperature. The cooperative effect of XZX $$+$$ YZY and XZY − YZX interaction is the most optimal to improve the robustness of all quantum correlations when the magnetic field is negative. When the magnetic field is positive, the effective of XZY − YZX interaction alone is more ideal to preserve different quantum correlations.

Relationship between the field local quadrature and the quantum discord of a photon-added correlated channel under the influence of scattering and phase fluctuation noise

We study quantum correlations and discord in a bipartite continuous variable hybrid system formed by linear combinations of coherent states $|\alpha\rangle$ and single photon added coherent states (SPACS) of the form $|\psi\rangle_{\text{dp(pa)}}= \mathcal{N}/\sqrt{2} (\hat{a}^\dagger |\alpha\rangle_a |\alpha\rangle_b \pm \hat{b}^\dagger |\alpha\rangle_a |\alpha\rangle_b)$. We stablish a relationship between the quantum discord with a local observable (the quadrature variance for one sub-system) under the influence of scattering and phase fluctuation noise. For the pure states the quantum correlations are characterized by means of measurement induced disturbance (MID) with simultaneous quadrature measurements. In a scenario where homodyne conditional measurements are available we show that the MID provides an easy way to select optimal phases to obtain information of the maximal correlations in the channels. The quantum correlations of these entangled states with channel losses are quantitatively characterized with the quantum discord (QD) with a displaced qubit projector. We observe that as scattering increases, QD decreases monotonically. At the same time for the state $|\psi\rangle_{\text{dp}}$, QD is more resistant to high phase fluctuations when the average photon number $n_0$ is bigger than zero, but if phase fluctuations are low, QD is more resistant if $n_0=0$. For the dp model with scattering, we obtain an analytical expression of the QD as a function of the observable quadrature variance in a local sub-system. This relation allows us to have a way to obtain the degree of QD in the channel by just measuring a local property observable such as the quadrature variance. For the other model this relation still exists but is explored numerically. This relation is an important result that allows to identify quantum processing capabilities in terms of just local observables.

Determining Complementary Properties with Quantum Clones.

In a classical world, simultaneous measurements of complementary properties (e.g., position and momentum) give a system's state. In quantum mechanics, measurement-induced disturbance is largest for complementary properties and, hence, limits the precision with which such properties can be determined simultaneously. It is tempting to try to sidestep this disturbance by copying the system and measuring each complementary property on a separate copy. However, perfect copying is physically impossible in quantum mechanics. Here, we investigate using the closest quantum analog to this copying strategy, optimal cloning. The coherent portion of the generated clones' state corresponds to "twins" of the input system. Like perfect copies, both twins faithfully reproduce the properties of the input system. Unlike perfect copies, the twins are entangled. As such, a measurement on both twins is equivalent to a simultaneous measurement on the input system. For complementary observables, this joint measurement gives the system's state, just as in the classical case. We demonstrate this experimentally using polarized single photons.

Macroscopic quantum measurements of noncommuting observables

Assuming a well-behaving quantum-to-classical transition, measuring large quantum systems should be highly informative with low measurement-induced disturbance, while the coupling between system and measurement apparatus is "fairly simple" and weak. Here, we show that this is indeed possible within the formalism of quantum mechanics. We discuss an example of estimating the collective magnetization of a spin ensemble by simultaneous measuring three orthogonal spin directions. For the task of estimating the direction of a spin-coherent state, we find that the average guessing fidelity and the system disturbance are nonmonotonic functions of the coupling strength. Strikingly, we discover an intermediate regime for the coupling strength where the guessing fidelity is quasi-optimal, while the measured state is almost not disturbed.