233,018 research outputs found
Time dynamics of quantum coherence and monogamy in a non-Markovian environment
The time evolution of the distribution and shareability of quantum coherence
of a tripartite system in a non-Markovian environment is examined. The total
coherence can be decomposed into various contributions, ranging from local,
global bipartite and global tripartite, which characterize the type of state.
We identify coherence revivals for non-Markovian systems for all the
contributions of coherence. The local coherence is found to be much more robust
under the environmental coupling due to an effective smaller coupling to the
reservoir. This allows us to devise a characterization of a quantum state in
terms of a coherence tuple on a multipartite state simply by examining various
combinations of reservoir couplings. The effect of the environment on the
shareability of quantum coherence, as defined using the monogamy of coherence,
is investigated and found that the sign of the monogamy is a preserved quantity
under the decoherence. We conjecture that the monogamy of coherence is a
conserved property under local incoherent processes
Local quantum coherence and superfluidity
We consider a model of bosons on a regular lattice with a kinetic energy due
to hopping among sites and a potential energy due to strong on site
interaction. A superfluid phase is expected when the ground state of the local
energy is doubly degenerate. We consider a new scheme of simmetry breaking
associated to the superfluid phase in which the order parameter is the
statistical average of the quantum coherence operator associated to the
superposition of the degenerate local ground states. In the strong coupling
limit a systematic expansion of the free energy can be performed in terms of
the hopping amplitude at constant order parameter. Within such an expansion we
obtain a self-consistent equation for the order parameter. The first order
approximation gives, in the case of degeneracy between single occupied and
empty state, the same result of the standard mean field approximation for the
``hard core bosons''. This new approach to the superfluid phase is shown to
have a natural application to the implementation of quantum computation on a
superfluid.Comment: 8 page
Sharing of Non-Local Advantage of Quantum Coherence by sequential observers
Non-local Advantage of Quantum Coherence(NAQC) or steerability of local
quantum coherence is a strong non-local resource based on coherence
complementarity relations. In this work, we provide an upper bound on the
number of observers who can independently steer the coherence of the observer
in the other wing in a scenario where half of an entangled pair of
spin- particles is shared between a single observer (Bob) in one
wing and several observers (Alices) on the other, who can act sequentially and
independently of each other. We consider one-parameter dichotomic POVMs for the
Alices and mutually unbiased basis in which Bob measures coherence in case of
the maximally entangled bipartite qubit state. We show that not more than two
Alices can exhibit NAQC when -norm of coherence measure is probed, whereas
for two other measures of coherence, only one Alice can reveal NAQC within the
same framework.Comment: 7 page
Coherence of local and global hulls
We give necessary and sufficient conditions for the hull of a coherent sheaf
to be coherent
Extracting quantum coherence via steering
As the precious resource for quantum information processing, quantum
coherence can be created remotely if the involved two sites are quantum
correlated. It can be expected that the amount of coherence created should
depend on the quantity of the shared quantum correlation, which is also a
resource. Here, we establish an operational connection between coherence
induced by steering and the quantum correlation. We find that the
steering-induced coherence quantified by such as relative entropy of coherence
and trace-norm of coherence is bounded from above by a known quantum
correlation measure defined as the one-side measurement-induced disturbance.
The condition that the upper bound saturated by the induced coherence varies
for different measures of coherence. The tripartite scenario is also studied
and similar conclusion can be obtained. Our results provide the operational
connections between local and non-local resources in quantum information
processing.Comment: almost published versio
Qubit Disentanglement and Decoherence via Dephasing
We consider whether quantum coherence in the form of mutual entanglement
between a pair of qubits is susceptible to decay that may be more rapid than
the decay of the coherence of either qubit individually. An instance of
potential importance for solid state quantum computing arises if embedded
qubits (spins, quantum dots, Cooper pair boxes, etc.) are exposed to global and
local noise at the same time. Here we allow separate phase-noisy channels to
affect local and non-local measures of system coherence. We find that the time
for decay of the qubit entanglement can be significantly shorter than the time
for local dephasing of the individual qubits.Comment: REVTeX, 9 pages, 1 figure, v2 with minor changes, reference adde
Distribution of coherence in multipartite systems under entropic coherence measure
The distribution of coherence in multipartite systems is one of the
fundamental problems in the resource theory of coherence. To quantify the
coherence in multipartite systems more precisely, we introduce new coherence
measures, incoherent-quantum (IQ) coherence measures, on bipartite systems by
the max- and min- relative entropies and provide the operational interpretation
in certain subchannel discrimination problem. By introducing the smooth max-
and min- relative entropies of incoherent-quantum (IQ) coherence on bipartite
systems, we exhibit the distribution of coherence in multipartite systems: the
total coherence is lower bounded by the sum of local coherence and genuine
multipartite entanglement. Besides, we find the monogamy relationship for
coherence on multipartite systems by incoherent-quantum (IQ) coherence
measures. Thus, the IQ coherence measures introduced here truly capture the
non-sharability of quantumness of coherence in multipartite context.Comment: 5.5+5 pages, 1 figur
Trapping Quantum Coherence in Local Energy Minima
Clusters of solid-state quantum devices have long-living metastable states of
local energy minima which may be used to store quantum information. The low to
vanishing rate of dissipation fulfils the prerequisite to maintain quantum
coherence. Then physical symmetrization of the devices could minimize the
couplings of the clusters to environmental degrees of freedom so to reduce the
rate of decoherence. Combined with various other error correction mechanisms
and methods, such designs and optimizations could render solid-state devices
useful for quantum information processing, which have the advantages of
flexibility in state manipulation and system scaling.Comment: Latex fil
Local cause of coherence in Boolean networks
We performed a numerical study on random Boolean networks with power-law rank
outdegree distributions to find local structural cause for the emergence of
high or low degree of coherence in binary state variables. The degree of
randomness and coherence of the binary sequence are measured by entropy and
mutual information, depending on local structure that consists of a node with a
highly connected, called hub and its upstream nodes, and types of Boolean
functions for the nodes. With a large number of output connections from a hub,
the effects of Boolean function on the hub are more prominent. The local
structures that give larger entropy tend to give rise to larger mutual
information. Based on the numerical results and structural conditions we
derived a time-independent transmission characteristic function of state
variables for the local structures. We obtained good relationships between the
numerical and analytical results, which indicate that dynamical properties from
the whole networks can be inferred from the differences in the local
structures.Comment: 6 pages, 6 figures, 3 tables. submitted to AROB 12th '0
Comment on "Unified view of quantum correlations and quantum coherence"
We show that contrary to what it is claimed in Phys. Rev. A \textbf{94},
022329 (2016), in general the local projective measurement that induces maximal
coherence loss is \textit{not} the projection onto the local basis that defines
the coherence of the system, at least for all quantum-incoherent states.Comment: 2 pages, no figure. An open question is raise
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