150 research outputs found
Analysis of quantum coherence for localized fermionic systems in an accelerated motion
Although quantum coherence is a well known phenomenon in quantum information theory and quantum optics, it has been investigated from the resource theory perspective only recently. Furthermore, quantum coherence has important implications in relativistic quantum information where the degradation of entanglement can be attributed to decoherence. In this paper, we investigate the quantum coherence of Dirac field modes localized in a cavity as observed by two relatively accelerated observers. The acceleration is assigned very small values and its effects are investigated in a perturbative regime. For this purpose, we use parameterized two-qubit pure entangled state and a Werner state. We find that coherence shows a periodic degradation due to accelerated motion. However, this degradation can be balanced by adjusting the durations of uniform and accelerated motion. Moreover, it is found that dynamics of quantum coherence closely resembles that of entanglement under the same settings. This similarity confirms the recent attempts to relate the resource theories of coherence and entanglement in a relativistic regime.publishedVersionUnit Licence Agreemen
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 constant acceleration. Due to relativistic motion
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 non-zero value.
These results hold for both single- and two-qubit relativistic motion. In the
GHZ and W states the coherence is distributed as correlations between the
qubits and is known as global coherence. But quantum coherence can also exist
due to the superposition within a qubit, the local coherence. To study the
properties of local coherence we investigate separable state. The GHZ state,
W-state and separable states contain only one type of coherence. Next we
consider the and star states in which both local and global
coherences coexist. We find that under relativistic motion both local and
global coherence show similar qualitative behaviour. Finally we derive analytic
expressions for the quantum coherence of -partite GHZ and W states where
qubits are subject to relativistic motion. 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.Comment: 18 page
Cohering and decohering power of massive scalar fields under instantaneous interactions
Employing a non-perturbative approach based on an instantaneous interaction
between a two-level Unruh-DeWitt detector and a massive scalar field, we
investigate the ability of the field to generate or destroy coherence in the
detector by deriving the cohering and decohering power of the induced quantum
evolution channel. For a field in a coherent state a previously unnoticed
effect is reported whereby the amount of coherence that the field generates
displays a revival pattern with respect to the size of the detector. It is
demonstrated that by including mass in a thermal field the set of maximally
coherent states of the detector decoheres less compared to a zero mass. In both
of the examples mentioned, by making a suitable choice of detector radius,
field energy and coupling strength it is possible to infer the mass of the
field by either measuring the coherence present in the detector in the case of
an interaction with a coherent field or the corresponding decoherence of a
maximally coherent state in the case of a thermal field. In view of recent
advances in the study of Proca metamaterials, these results suggest the
possibility of utilising the theory of massive electromagnetism for the
construction of novel applications for use in quantum technologies
Classification of a supersolid: Trial wavefunctions, Symmetry breakings and Excitation spectra
A state of matter is characterized by its symmetry breaking and elementary
excitations.
A supersolid is a state which breaks both translational symmetry and internal
symmetry.
Here, we review some past and recent works in phenomenological
Ginsburg-Landau theories, ground state trial wavefunctions and microscopic
numerical calculations. We also write down a new effective supersolid
Hamiltonian on a lattice.
The eigenstates of the Hamiltonian contains both the ground state
wavefunction and all the excited states (supersolidon) wavefunctions. We
contrast various kinds of supersolids in both continuous systems and on
lattices, both condensed matter and cold atom systems. We provide additional
new insights in studying their order parameters, symmetry breaking patterns,
the excitation spectra and detection methods.Comment: REVTEX4, 19 pages, 3 figure
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