43 research outputs found
Bounds on an effective thermalization beyond the Zeno limit
Developing protocols for preserving information in quantum systems is a
central quest for implementing realistic quantum computation. In this regard,
the quantum Zeno effect has emerged as a widely utilized technique to safeguard
classical information stored in quantum systems. However, existing results
pertaining to this method often assume operations performed infinitely fast on
the system of interest, which only serves as an approximation to real-world
scenarios where the temporal resolution of any experimental apparatus is
inherently finite. In this study, we go beyond this conventional assumption and
derive the effective Zeno dynamics for any time interval between operations.
Our analysis considers a qubit undergoing thermalization, as described by a
generalized amplitude damping channel, while the operations performed consist
of projections onto an orthonormal basis that may or may not coincide with the
pointer basis to which the system is thermalizing. By obtaining the probability
of successfully storing a bit of information after a given time, we investigate
the performance of the protocol in two important scenarios: the limit of many
interventions, with a first-order correction to the Zeno limit, and the limit
of very few interventions. In doing so, we provide valuable insights into the
protocol's performance by establishing bounds on its efficacy. These findings
enhance our understanding of the practical applicability of the quantum Zeno
effect in preserving classical information stored in quantum systems, allowing
for better design and optimization of quantum information processing protocols
The Elephant Quantum Walk
We explore the impact of long-range memory on the properties of a family of
quantum walks in a one-dimensional lattice and discrete time, which can be
understood as the quantum version of the classical "Elephant Random Walk"
non-Markovian process. This Elephant Quantum Walk is robustly superballistic
with the standard deviation showing a constant exponent, , whatever the quantum coin operator, on which the diffusion coefficient is
dependent. On the one hand, this result indicates that contrarily to the
classical case, the degree of superdiffusivity in quantum non- Markovian
processes of this kind is mainly ruled by the extension of memory rather than
other microscopic parameters that explicitly define the process. On the other
hand, these parameters reflect on the diffusion coefficient.Comment: 4 figures, any comments is welcome. Accepted in PR
Conditional quantum thermometry -- enhancing precision by measuring less
Taking accurate measurements of the temperature of quantum systems is a
challenging task. The mathematical peculiarities of quantum information make it
virtually impossible to measure with infinite precision. In the present letter,
we introduce a generalize thermal state, which is conditioned on the pointer
states of the available measurement apparatus. We show that this conditional
thermal state outperforms the Gibbs state in quantum thermometry. The origin
for the enhanced precision can be sought in its asymmetry quantified by the
Wigner-Yanase-Dyson skew information. This additional resource is further
clarified in a fully resource-theoretic analysis, and we show that there is a
Gibbs-preserving map to convert a target state into the conditional thermal
state. Finally, we relate the quantum J-divergence between the conditional
thermal state and the same target state to quantum heat.Comment: 5+6 pages, 2 figure
Distributed correlations and information flows within a hybrid multipartite quantum-classical system
Understanding the non-Markovian mechanisms underlying the revivals of quantum
entanglement in the presence of classical environments is central in the theory
of quantum information. Tentative interpretations have been given by either the
role of the environment as a control device or the concept of hidden
entanglement. We address this issue from an information-theoretic point of
view. To this aim, we consider a paradigmatic tripartite system, already
realized in the laboratory, made of two independent qubits and a random
classical field locally interacting with one qubit alone. We study the
dynamical relationship between the two-qubit entanglement and the genuine
tripartite correlations of the overall system, finding that collapse and
revivals of entanglement correspond, respectively, to raise and fall of the
overall tripartite correlations. Interestingly, entanglement dark periods can
enable plateaux of nonzero tripartite correlations. We then explain this
behavior in terms of information flows among the different parties of the
system. Besides showcasing the phenomenon of the freezing of overall
correlations, our results provide new insights on the origin of retrieval of
entanglement within a hybrid quantum-classical system.Comment: 9 pages, 5 figures. To appear on Phys. Rev.