383 research outputs found
Characterization of quantum dynamics using quantum error correction
Characterizing noisy quantum processes is important to quantum computation
and communication (QCC), since quantum systems are generally open. To date, all
methods of characterization of quantum dynamics (CQD), typically implemented by
quantum process tomography, are \textit{off-line}, i.e., QCC and CQD are not
concurrent, as they require distinct state preparations. Here we introduce a
method, "quantum error correction based characterization of dynamics", in which
the initial state is any element from the code space of a quantum error
correcting code that can protect the state from arbitrary errors acting on the
subsystem subjected to the unknown dynamics. The statistics of stabilizer
measurements, with possible unitary pre-processing operations, are used to
characterize the noise, while the observed syndrome can be used to correct the
noisy state. Our method requires at most configurations to
characterize arbitrary noise acting on qubits.Comment: 7 pages, 2 figures; close to the published versio
Quantum Critical Environment Assisted Quantum Magnetometer
A central qubit coupled to an Ising ring of qubits, operating close to a
critical point is investigated as a potential precision quantum magnetometer
for estimating an applied transverse magnetic field. We compute the Quantum
Fisher information for the central, probe qubit with the Ising chain
initialized in its ground state or in a thermal state. The non-unitary
evolution of the central qubit due to its interaction with the surrounding
Ising ring enhances the accuracy of the magnetic field measurement. Near the
critical point of the ring, Heisenberg-like scaling of the precision in
estimating the magnetic field is obtained when the ring is initialized in its
ground state. However, for finite temperatures, the Heisenberg scaling is
limited to lower ranges of values.Comment: 10 pages, 9 figure
Quantum Fisher and Skew information for Unruh accelerated Dirac qubit
We develop a Bloch vector representation of Unruh channel for a Dirac field
mode. This is used to provide a unified, analytical treatment of quantum Fisher
and Skew information for a qubit subjected to the Unruh channel, both in its
pure form as well as in the presence of experimentally relevant external noise
channels. The time evolution of Fisher and Skew information is studied along
with the impact of external environment parameters such as temperature and
squeezing. The external noises are modelled by both purely dephasing phase
damping as well as the squeezed generalized amplitude damping channels. An
interesting interplay between the external reservoir temperature and squeezing
on the Fisher and Skew information is observed, in particular, for the action
of the squeezed generalized amplitude damping channel. It is seen that for some
regimes, squeezing can enhance the quantum information against the
deteriorating influence of the ambient environment. Similar features are also
observed for the analogous study of Skew information, highlighting the similar
origin of the Fisher and Skew information.Comment: 12 pages, 10 figure
Characterization of Unruh Channel in the context of Open Quantum Systems
We show through the Choi matrix approach that the effect of Unruh
acceleration on a qubit is similar to the interaction of the qubit with a
vacuum bath, despite the finiteness of the Unruh temperature. Thus, rather
counterintuitvely, from the perspective of decoherence in this framework, the
particle experiences a vacuum bath with a temperature-modified interaction
strength, rather than a thermal bath. We investigate how this "relativistic
decoherence" is modified by the presence of environmentally induced
decoherence, by studying the degradation of quantum information, as quantified
by parameters such as nonlocality, teleportation fidelity, entanglement,
coherence and quantum measurement-induced disturbance (a discord-like measure).
Also studied are the performance parameters such as gate and channel fidelity.
We highlight the distinction between dephasing and dissipative environmental
interactions, by considering the actions of quantum non-demolition and squeezed
generalized amplitude damping channels, respectively, where, in particular,
squeezing is shown to be a useful quantum resource.Comment: 15 pages, 19 figure
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