Quantum memory in non-inertial frames

2014

The quantum and classical correlations are quantified by means of the coherent and mutual information, respectively, where we use the single-mode approximation. It is shown that the users can communicate in an optimal way for small values of accelerations. The capacity of accelerated channel is investigated for different classes of initial states. It is shown that the capacities of the traveling channels depend on the frame in which the accelerated channels are observed in and the initial shared state between the partners. In some frames, the capacities decay as the accelerations of both qubit increase. The decay rate is larger if the partners initially share a maximum entangled state. The possibility of using the accelerated quantum channels to perform quantum coding protocol is discussed. The amount of decoded information is quantified for different cases, where it decays as the partner's accelerations increase to reach its minimum bound. This minimum bound depends on the initial shared states, and it is large for maximum entangled state.

2010

These authors contributed equally to this work.

Nature Physics, 2011

A quantum memory for light is a key element for the realization of future quantum information networks. Requirements for a good quantum memory are versatility (allowing a wide range of inputs) and preservation of quantum information in a way unattainable with any classical memory device. Here we demonstrate such a quantum memory for continuous-variable entangled states, which play a fundamental role in quantum information processing. We store an extensive alphabet of two-mode 6.0dB squeezed states obtained by varying the orientation of squeezing and the displacement of the states. The two components of the entangled state are stored in two room-temperature cells separated by 0.5m, one for each mode, with a memory time of 1ms. The true quantum character of the memory is rigorously proved by showing that the experimental memory fidelity 0.52+/-0.02 significantly exceeds the benchmark of 0.45 for the best possible classical memory for a range of displacements.

arXiv: Quantum Physics, 2018

Quantum temporal correlations exhibited by violations of Leggett-Garg Inequality (LGI) and Temporal Steering Inequality (TSI) are in general found to be non-increasing under decoherence channels when probed on two-qubit pure entangled states. We study the action of decoherence channels, such as amplitude damping, phase-damping and depolarising channels when partial memory is introduced in a way such that two consecutive uses of the channels are time-correlated. We show that temporal correlations demonstrated by violations of the above temporal inequalities can be protected against decoherence using the effect of memory.

International Journal of Theoretical Physics, 2019

Semi-Bell states are exploited for storing and sending information in non-inertial frames. In this paper, we consider four types of semi-bell states, |Φ ± α = α|0 |0 ± √ 1 − α 2 |1 |1 and |Ψ ± α = α|0 |1 ± √ 1 − α 2 |1 |0 , and study entanglements and other quantum correlations of these states from the viewpoint of an accelerated and an inertial observers by computing such measures as negativity, quantum coherence, and purity of these states. As expected, these measures degrade for semi-bell states with increasing acceleration. The states, however, exhibit different types of degradation depending on the statistics of the particles. Entanglement, coherence, and purity of bosonic states degrade more rapidly than do states with fermionic statistics. A duality exists in the measures of the two types of semibell states and for the maximally entangled states (α = 1 √ 2), there is no difference between the measures of |Φ ± α and |Ψ ± α. In the fermionic case, differences of the measures between the |Φ ± α and |Ψ ± α states are greater for large values of acceleration, while in the bosonic case, their subtractions are larger for small values of acceleration.

Physical Review A, 2009

I explore entanglement dynamics in examples of quantum memories, decoherence free subspaces (DFS) and noiseless subsystems (NS), to determine how a complete loss of entanglement affects the ability of these techniques to protect quantum information. Using negativity and concurrence as entanglement measures, I find that in general there is no correlation between the complete loss of entanglement in the system and the fidelity of the stored quantum information. These results complement previous results in which quantum protocols not explictly based on entanglement exhibit little correlation between ESD and the accuracy of the given protocol.

In this paper, some properties of multi-qubit states traveling in non-inertial frames are investigated, where we assume that all particles are accelerated. These properties are including fidelities, capacities and entanglement of the accelerated channels for three different states, namely, Greeberger-Horne-Zeilinger (GHZ) state, GHZ-like state and W-state. It is shown here that all these properties are decreased as the accelerations of the moving particles are increased. The obtained results show that the GHZ-state is the most robust one comparing to the others, where the degradation rate is less than that for the other states particularly in the second Rindler region. Also, it is shown here that the entangled property doesn't change in the accelerated frames. Additionally, the paper shows that the degree of entanglement decreases as the accelerations of the particles increase in the first Rindler region. However in the second region, where all subsystems are disconnected at zero acceleration, entangled channels are generated as the acceleration increases.

Physical Review A, 2008

A procedure to obtain the dynamics of $N$ independent qudits ($d$-level systems) each interacting with its own reservoir, for any arbitrary initial state, is presented. This is then applied to study the dynamics of the entanglement of two qubits, initially in an extended Werner-like mixed state with each of them in a zero temperature non-Markovian environment. The dependence of the entanglement dynamics on the purity and degree of entanglement of the initial states and on the amount of non-Markovianity is also given. This extends the previous work about non-Markovian effects on the two-qubit entanglement dynamics for initial Bell-like states [B. Bellomo \textit{et al.}, Phys. Rev. Lett. \textbf{99}, 160502 (2007)]. The effect of temperature on the two-qubit entanglement dynamics in a Markovian environment is finally obtained.

Nature Physics, 2010

A quantum memory for light is a key element for the realization of future quantum information networks. Requirements for a good quantum memory are (i) versatility (allowing a wide range of inputs) and (ii) true quantum coherence (preserving quantum information). Here we demonstrate such a quantum memory for states possessing Einstein-Podolsky-Rosen (EPR) entanglement. These multi-photon states are two-mode squeezed by 6.0 dB with a variable orientation of squeezing and displaced by a few vacuum units. This range encompasses typical input alphabets for a continuous variable quantum information protocol. The memory consists of two cells, one for each mode, filled with cesium atoms at room temperature with a memory time of about 1msec. The preservation of quantum coherence is rigorously proven by showing that the experimental memory fidelity 0.52(2) significantly exceeds the benchmark of 0.45 for the best possible classical memory for a range of displacements.

2010