8,376 research outputs found
Testing quantum adiabaticity with quench echo
Adiabaticity of quantum evolution is important in many settings. One example
is the adiabatic quantum computation. Nevertheless, up to now, there is no
effective method to test the adiabaticity of the evolution when the
eigenenergies of the driven Hamiltonian are not known. We propose a simple
method to check adiabaticity of a quantum process for an arbitrary quantum
system. We further propose a operational method for finding a uniformly
adiabatic quench scheme based on Kibble-Zurek mechanism for the case when the
initial and the final Hamiltonians are given. This method should help in
implementing adiabatic quantum computation.Comment: This is a new version. Some typos in the New Journal of Physics
version have been correcte
Mesoscopic circuits with charge discreteness:quantum transmission lines
We propose a quantum Hamiltonian for a transmission line with charge
discreteness. The periodic line is composed of an inductance and a capacitance
per cell. In every cell the charge operator satisfies a nonlinear equation of
motion because of the discreteness of the charge. In the basis of one-energy
per site, the spectrum can be calculated explicitly. We consider briefly the
incorporation of electrical resistance in the line.Comment: 11 pages. 0 figures. Will be published in Phys.Rev.
Sensitive Chemical Compass Assisted by Quantum Criticality
The radical-pair-based chemical reaction could be used by birds for the
navigation via the geomagnetic direction. An inherent physical mechanism is
that the quantum coherent transition from a singlet state to triplet states of
the radical pair could response to the weak magnetic field and be sensitive to
the direction of such a field and then results in different photopigments in
the avian eyes to be sensed. Here, we propose a quantum bionic setup for the
ultra-sensitive probe of a weak magnetic field based on the quantum phase
transition of the environments of the two electrons in the radical pair. We
prove that the yield of the chemical products via the recombination from the
singlet state is determined by the Loschmidt echo of the environments with
interacting nuclear spins. Thus quantum criticality of environments could
enhance the sensitivity of the detection of the weak magnetic field.Comment: 4 pages, 3 figure
Mixed-state fidelity and quantum criticality at finite temperature
We extend to finite temperature the fidelity approach to quantum phase
transitions (QPTs). This is done by resorting to the notion of mixed-state
fidelity that allows one to compare two density matrices corresponding to two
different thermal states. By exploiting the same concept we also propose a
finite-temperature generalization of the Loschmidt echo. Explicit analytical
expressions of these quantities are given for a class of quasi-free fermionic
Hamiltonians. A numerical analysis is performed as well showing that the
associated QPTs show their signatures in a finite range of temperatures.Comment: 7 pages, 4 figure
Critical dynamics of decoherence
We study decoherence induced by a dynamic environment undergoing a quantum
phase transition. Environment's susceptibility to perturbations - and,
consequently, efficiency of decoherence - is amplified near a critical point.
Over and above this near-critical susceptibility increase, we show that
decoherence is dramatically enhanced by non-equilibrium critical dynamics of
the environment. We derive a simple expression relating decoherence to the
universal critical exponents exhibiting deep connections with the theory of
topological defect creation in non-equilibrium phase transitions.Comment: 8 pages; version accepted in PR
Enhancement of Distribution System State Estimation Using Pruned Physics-Aware Neural Networks
Realizing complete observability in the three-phase distribution system
remains a challenge that hinders the implementation of classic state estimation
algorithms. In this paper, a new method, called the pruned physics-aware neural
network (P2N2), is developed to improve the voltage estimation accuracy in the
distribution system. The method relies on the physical grid topology, which is
used to design the connections between different hidden layers of a neural
network model. To verify the proposed method, a numerical simulation based on
one-year smart meter data of load consumptions for three-phase power flow is
developed to generate the measurement and voltage state data. The IEEE 123-node
system is selected as the test network to benchmark the proposed algorithm
against the classic weighted least squares (WLS). Numerical results show that
P2N2 outperforms WLS in terms of data redundancy and estimation accuracy
Quantum Critical Dynamics of A Qubit Coupled to An Isotropic Lipkin-Meshkov-Glick Bath
We explore a dynamic signature of quantum phase transition (QPT) in an
isotropic Lipkin-Meshkov-Glick (LMG) model by studying the time evolution of a
central qubit coupled to it. We evaluate exactly the time-dependent purity,
which can be used to measure quantum coherence, of the central qubit. It is
found that distinctly different behaviors of the purity as a function of the
parameter reveal clearly the QPT point in the system. It is also clarified that
the present model is equivalent to an anti Jaynes-Cummings model under certain
conditions.Comment: 8 pages, 4 figure
Entanglement and quantum phase transition in the extended Hubbard model
We study quantum entanglement in one-dimensional correlated fermionic system.
Our results show, for the first time, that entanglement can be used to identify
quantum phase transitions in fermionic systems.Comment: 5 pages, 4 figure
Ground state fidelity in bond-alternative Ising chains with Dzyaloshinskii-Moriya interactions
A systematic analysis is performed for quantum phase transitions in a
bond-alternative one-dimensional Ising model with a Dzyaloshinskii-Moriya (DM)
interaction by using the fidelity of ground state wave functions based on the
infinite matrix product states algorithm. For an antiferromagnetic phase, the
fidelity per lattice site exhibits a bifurcation, which shows spontaneous
symmetry breaking in the system. A critical DM interaction is inversely
proportional to an alternating exchange coupling strength for a quantum phase
transition. Further, a finite-entanglement scaling of von Neumann entropy with
respect to truncation dimensions gives a central charge c = 0.5 at the critical
point.Comment: 6 pages, 4 figure
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