Infinite Acceleration Limit Research Articles

Schwinger correlation of Dirac fields in accelerated frames

We study the Schwinger correlation of Dirac fields in the noninertial frames under the influences of both constant and pulsed electric fields. We use both the entanglement negativity and quantum mutual information between particle and antiparticle as the indicator of the Schwinger correlation observed by the accelerated observers. We find that the Schwinger correlation in the inertial frames is the largest. With the increase of acceleration of the observers, the Schwinger correlation becomes smaller and smaller, but does not vanish in the limit of infinite acceleration. For the given acceleration, the Schwinger correlation is a nonmonotonic function of the electric field intensity, and there is an optimal value of electric field intensity for which the Schwinger correlation is the largest. In the case of pulsed electric fields, the Schwinger correlation is also the nonmonotonic function of pulsed width, which suggests the existence of optimal pulsed width for observing Schwinger correlation.

Tripartite Uncertainty, Quantum, and Classical Correlations Dynamics under Unruh Effect

AbstractHow the dynamics of classical and quantum correlations due to the Unruh effect are reflected in the properties of tripartite entropic uncertainty is investigated. It is found that, despite the quantum correlations disappearing at the limit of infinite acceleration, the uncertainty about the measurement outcome is at its minimum. This is due to the three‐qubit system still containing classic correlations at that stage of acceleration. Additionally, the decrease in the entropic uncertainty when the measured qubit interacts strongly with the scalar field can be attributed to the increase in classical correlations. Furthermore, it is found that the entropic uncertainty is fully anti‐correlated to classical correlations, and minimal uncertainty can be obtained even in the absence of quantum correlations. A tremendously tight constraint that effectively defined the properties of tripartite entropic uncertainty based on the difference between the total correlation and the Holevo quantities is achieved.

Quantum correlations and coherence in a moving Unruh–deWitt detector

In this paper, we investigate the quantum correlations and coherence of two accelerating Unruh–deWitt detectors coupled to a scalar field in 3+1 Minkowski space–time. We show that the entanglement is completely destroyed in the limit of infinite acceleration while the local quantum uncertainty and l1-norm of coherence remain nonzero. In addition, we also highlight the role of Unruh temperature and energy spacing of detectors on quantum correlations for different choices of initial states.

Pentapartite Entanglement Measures of GHZ and W-Class State in the Noninertial Frame.

We study both pentapartite GHZ and W-class states in the noninertial frame and explore their entanglement properties by carrying out the negativities including 1-4, 2-3, and 1-1 tangles, the whole entanglement measures such as algebraic and geometric averages and , and von Neumann entropy. We illustrate graphically the difference between the pentapartite GHZ and W-class states. We find that all 1-4, 2-3 tangles and the whole entanglements, which are observer dependent, degrade more quickly as the number of accelerated qubits increases. The entanglements of these quantities still exist even at the infinite acceleration limit. We also notice that all 1-1 tangles of pentapartite GHZ state where , whereas all 1-1 tangles of the W-class state and are unequal to zero, e.g., but and disappear at and , respectively. We notice that the entanglement of the pentapartite GHZ and W-class quantum systems decays faster as the number of accelerated particles increases. Moreover, we also illustrate the difference of von Neumann entropy between them and find that the entropy in the pentapartite W-class state is greater than that of GHZ state. The von Neumann entropy in the pentapartite case is more unstable than those of tripartite and tetrapartite subsystems in the noninertial frame.

Accessible and inaccessible quantum coherence in relativistic quantum systems

The quantum coherence of a multipartite system is investigated when some of the parties are moving with uniform acceleration and the analysis is carried out using the single-mode approximation. Due to acceleration the quantum coherence is divided into two parts as accessible and inaccessible coherence. First we investigate tripartite systems, considering both GHZ and $W$ states. We find that the quantum coherence of these states does not vanish in the limit of infinite acceleration, rather asymptoting to a nonzero value. These results hold for both single- and two-qubit acceleration. In the GHZ and $W$ states the coherence is distributed as correlations between the qubits and is known as global coherence. However, quantum coherence can also exist due to the superposition within a qubit, the local coherence. To study the properties of local coherence we investigate a separable state. The GHZ state, $W$ state, and separable states contain only one type of coherence. Next we consider the $W\overline{W}$ and star states in which both local and global coherences coexist. We find that under uniform acceleration both local and global coherence show similar qualitative behavior. Finally, we derive analytic expressions for the quantum coherence of $N$-partite GHZ and $W$ states for $n<N$ accelerating qubits. We find that the quantum coherence of a multipartite GHZ state falls exponentially with the number of accelerated qubits, whereas for multipartite $W$ states the quantum coherence decreases only polynomially. We conclude that $W$ states are more robust to Unruh decoherence and discuss some potential applications in satellite-based quantum communication and black-hole physics.

Rindler Physics on the String Worldsheet.

We construct the tensionless limit of bosonic string theory in terms of a family of worldsheets with increasing acceleration and show that the null string emerges in the limit of infinite acceleration when the Rindler horizon is hit. We discover a novel phenomenon we call null string complementarity, which gives two distinct observer-dependent pictures of the emergence of open string physics from closed strings in the tensionless limit. The closed string vacuum as observed by the inertial worldsheet turns into a D instanton in the tensionless limit, while in the complementary picture from the accelerated worldsheet, one sees the emergence of a D-25 brane. We finally discuss approaching the Rindler horizon through time evolution at constant acceleration and also show how an open string picture arises very naturally.

Multipartite Quantum Clock Synchronization under The Influence of Unruh Thermal Noise

AbstractA protocol for multipartite quantum clock synchronization is performed under the influence of Unruh thermal noise. The dynamics of multipartite quantum system consisting of Unruh–DeWitt detectors when one of the detectors is accelerated are obtained. To estimate the time difference between the clocks, the time probability is calculated and how the probability is influenced by the Unruh thermal noise and other factors is analyzed. It is shown that both relativistic motion and interaction between the atom and the external scalar field affect the choice of optimal number of excited atoms in the initial state, which leads to a higher clock adjustment accuracy. Time probabilities for different types of initial states approach the same value in the limit of infinite acceleration, while tend to different minimums with increasing number of atoms. In addition, the accuracy of clock synchronization using a pair of entangled clocks in two‐party system is always higher than in a multipartite system, while the optimal Z‐type multipartite initial state always performs better than the W‐type state.

An investigation of some quantum correlations of Dirac fields in noninertial frames

In this paper, some concepts of quantum correlations, such as one-way quantum deficit, purity, and entanglement of formation are investigated between the modes of Dirac fields in noninertial frames. We consider two bipartite divisions of a tripartite system constructed by initial Werner states, which is shared between two relatively accelerated observers. The degradation of these quantum correlations is shown when the acceleration parameter increases. However, a nonzero amount of correlations survives even at infinite acceleration limit. Furthermore, we study the inevitable influence of mixedness factor of initial state on the quantum correlations behaviour. Finally, we review our calculation beyond single-mode approximation and point out some differences and similarities between the two regimes.

Quantum coherence of fermionic systems in noninertial frames beyond the single-mode approximation

In this paper, we investigate the behavior of the quantum coherence for bipartite fermionic systems in noninertial frames beyond the single-mode approximation. It is shown a redistribution of coherence between particle and antiparticle modes, and the behavior in terms of coherence for fermionic systems is convergent in the infinite acceleration limit. We demonstrate that the physical accessible coherence is not always destroyed with the increase in acceleration, which is different from the features of entanglement in the accelerated frame. Besides, we obtain a quantitative relationship about the redistribution of coherence via the \(l_1\)-norm measure. It is worth mentioning that a rotation operation can change the coherence values, since the amount of coherence is related to the selection of reference basis.

Quantum coherence behaviors of fermionic system in non-inertial frame

In this paper, we analyze the quantum coherence behaviors of a single qubit in the relativistic regime beyond the single-mode approximation. Firstly, we investigate the freezing condition of quantum coherence in fermionic system. We also study the quantum coherence tradeoff between particle and antiparticle sector. It is found that there exists quantum coherence transfer between particle and antiparticle sector, but the coherence lost in particle sector is not entirely compensated by the coherence generation of antiparticle sector. Besides, we emphatically discuss the cohering power and decohering power of Unruh channel with respect to the computational basis. It is shown that cohering power is vanishing and decohering power is dependent of the choice of Unruh mode and acceleration. Finally, we compare the behaviors of quantum coherence with geometric quantum discord and entanglement in relativistic setup. Our results show that this quantifiers in two region converge at infinite acceleration limit, which implies that this measures become independent of Unruh modes beyond the single-mode approximations. It is also demonstrated that the robustness of quantum coherence and geometric quantum discord are better than entanglement under the influence of acceleration, since entanglement undergoes sudden death.

Residual entanglement of accelerated fermions is useful

The non-vanishing residual entanglement, between the fermionic modes in the infinite acceleration limit, does not violate CHSH inequality, therefore it is not non-local. In this paper, we study the usefulness of the residual fermionic entanglement in single mode approximation and beyond single mode approximation. It is shown that there are some cases where the CHSH inequality is not violated by the residual entanglement, but the state is useful for quantum teleportation. Conditions for the violation of the CHSH inequality in terms of the “presence probability” of the particle in different Rindler regions are given for the state to be useful for teleportation and superdense coding.

Tetrapartite entanglement of fermionic systems in noninertial frames

Under the single-mode approximate, we theoretically investigate the properties of entanglement for four-mode Fermi GHZ state when some observers are in uniform acceleration with respective to others. We use two different definitions for calculating the degree of entanglement, i.e., the arithmetic and geometric average of tangles. It is shown that a maximally entangled state in an inertial frame shall become one with less entanglement in noninertial frame and the partial and the whole entanglements decrease as the number of accelerated observers. In particular, for 1–3 accelerated observers, there is still entanglement in the limit of infinite acceleration for all tangles. However, the sudden death shall be present for both the whole and the part one only when four observers are accelerated. In addition, we make a comparison for these two definitions of entanglement. It is interesting to notice that, for three accelerated observers, the difference first increases and then decreases as the increasing parameter r.

No survival of Nonlocalilty of fermionic quantum states with alpha vacuum in the infinite acceleration limit

In this article, we investigate the nonlocal behavior of the quantum state of fermionic system having the alpha vacuum. We evaluate the maximum violation of CHSH inequality in the quantum state. Even when the maximally entangled quantum state is initially shared it cannot violate the CHSH inequality, regardless of any alpha vacuum, when the infinite acceleration is applied. It means that the nonlocality of the quantum state in fermionic system with the alpha vacuum cannot survive in the infinite acceleration limit.

Tripartite entanglement of fermionic system in accelerated frames

The dynamics of tripartite entanglement of fermionic system in noninertial frames through linear contraction criterion when one or two observers are accelerated is investigated. In one observer accelerated case the entanglement measurement is not invariant with respect to the partial realignment of different subsystems and for two observers accelerated case it is invariant. It is shown that the acceleration of the frame does not generate entanglement in any bipartite subsystems. Unlike the bipartite states, the genuine tripartite entanglement does not completely vanish in both one observer accelerated and two observers accelerated cases even in the limit of infinite acceleration. The degradation of tripartite entanglement is fast when two observers are accelerated than when one observer is accelerated. It is shown that tripartite entanglement is a better resource for quantum information processing than the bipartite entanglement in noninertial frames.

Quantum Fisher information in noninertial frames

We investigate the performance of quantum Fisher information (QFI) under the Unruh-Hawking effect, where one of the observers (e.g., Rob) is uniformly accelerated with respect to other partners. In the context of relativistic quantum information theory, we demonstrate that quantum Fisher information, as an important measure of the information content of quantum states, has a rich and subtle physical structure compared with entanglement or Bell nonlocality. In this work, we mainly focus on the parametrized (and arbitrary) pure two-qubit states, where the weight parameter $\ensuremath{\theta}$ and phase parameter $\ensuremath{\phi}$ are naturally introduced. Intriguingly, we prove that QFI with respect to $\ensuremath{\theta}$ (${\mathcal{F}}_{\ensuremath{\theta}}$) remains unchanged for both scalar and Dirac fields. Meanwhile, we observe that QFI with respect to $\ensuremath{\phi}$ (${\mathcal{F}}_{\ensuremath{\phi}}$) decreases with the increase of acceleration $r$ but remains finite in the limit of infinite acceleration. More importantly, our results show that the symmetry of ${\mathcal{F}}_{\ensuremath{\phi}}$ (with respect to $\ensuremath{\theta}=\ensuremath{\pi}/4$) has been broken by the influence of the Unruh effect for both cases.

Entanglement dynamics of two cavities interacting with reservoir in noninertial frame

We investigate the entanglement dynamics of two cavities interacting respectively with reservoir in non-inertial frames. We consider not only the influence of acceleration, but also the influence of different rates between right and left components of the Unruh single-particle state on entanglement. The result shows that the reservoir-entanglement will increase with the decrease of the cavity-entanglement when the acceleration parameter is fixed. In addition, there appears the redistribution of entanglement between particle mode and antiparticle mode, when the initial state is in a maximal by entangled state with |qR|=1. We also find that the sudden death of entanglement happens in infinite acceleration limit when |qR|=|qL|=1/√2, whereas the death of entanglement happens at finite acceleration when qR2.

Quantum discord amplification of fermionic systems in an accelerated frame

Quantum discord of fermionic systems in the relativistic regime, that is, beyond the single-mode approximation (SMA) is investigated. It is shown that quantum discord is amplified for the fermionic system in non-inertial frames irrespective of the choice of state, region and level of mixedness. This ensures that the phenomenon of amplification can actually happen in the relativistic regime. It is seen that quantum discord converges at infinite acceleration limit, which means that it becomes independent of $$q_{R}$$qR (Unruh modes) beyond SMA. This implies that most of the tensor product structures already used in the literature to compute quantum field correlations in relativistic quantum information cannot give rise to physical results. The dynamics of quantum discord is investigated under amplitude damping, depolarizing and flipping channels. The vanishing behavior of quantum discord is seen for higher level of decoherence in the infinite acceleration limit. The depolarizing channel dominantly affects the fermionic quantum discord as compared to the amplitude damping channel. It means that the depolarizing channel has most destructive influence on the discord of the fermionic systems. Moreover, the effect of environment on the discord is much stronger than that of the acceleration of non-inertial frames.

Dynamics of Fermionic Geometric Discord beyond Single-Mode Approximations

Geometric quantum discord of fermionic systems in the relativistic regime, that is, beyond the single-mode approximation, is investigated. It is shown that geometric quantum discord for the fermionic systems in non-inertial frames converges at an infinite acceleration limit, which means that the fermionic systems become independent of the choice of Unruh modes (qR) beyond single-mode approximation. The discord may vanish or be retained depending upon the level of mixedness of the fermionic system. The dynamics of geometric discord are investigated under amplitude damping, depolarizing, phase damping and flipping channels. The vanishing behavior of discord is seen for a higher level of decoherence in the infinite acceleration limit. The depolarizing channel dominantly affects the fermionic geometric discord as compared to the amplitude and phase damping channels. This implies that the depolarizing channel has most destructive influence on the discord of the fermionic systems. However, the flipping channels have a symmetrical effect on the discord. Moreover, the discord heavily depends on the mixedness parameter of the quantum state of the fermionic systems in accelerated frames beyond single-mode approximation.

Measurement-induced-nonlocality via the Unruh effect

Treated beyond the single-mode approximation, Measurement-Induced-Nonlocality (MIN) is investigated for both Dirac and Bosonic fields in non-inertial frames. Two distinct differences between the Dirac and Bosonic fields are: (i) the MIN for Dirac fields persists for any acceleration, while the quantity for Bosonic fields does decay to zero in the infinite acceleration limit; (ii) the dynamic behaviors of the MIN for Dirac fields is quite different from the Bosonic fields case. Besides, we also study the nonlocality for Dirac fields and find that the MIN is more general than the quantum nonlocality related to violation of Bell’s inequalities. Meanwhile some discussions of geometric discord are presented too.

Entanglement and discord: Accelerated observations of local and global modes

We investigate the amount of entanglement and quantum discord extractable from a two mode squeezed state as considered from the viewpoint of two observers, Alice (inertial) and Rob (accelerated). We find that using localized modes produces qualitatively different correlation properties for large accelerations than do Unruh modes. Specifically, the entanglement undergoes a sudden death as a function of acceleration and the discord asymptotes to zero in the limit of infinite acceleration. We conclude that the previous Unruh mode analyses do not determine the acceleration dependent entanglement and discord degradation of a given quantum state.