arXiv subjects

Milajiguli Rexiti

Publications and source records attributed to Milajiguli Rexiti.

12 recordsLinked to original sources

arXiv2026

Entanglement-Assisted Timing Optimization for Discriminating Amplitude-Damping Dynamics

We analyze minimum-error discrimination of two qubit dynamical processes generated by phase-covariant amplitude-damping Lindbladians in a single-use scenario. The optimization involves both the input probe, possibly entangled with an isolated ancilla, and the interrogation time. For unassisted probes we obtain a closed expression for the optimal trace-norm distinguishability at fixed time, with distinct interior and boundary branches. For entanglement-assisted probes, the common phase covariance of the two channels reduces the diamond-norm optimization to a one-parameter Schmidt family. The resulting formula gives transparent sufficient conditions for fixed-time entanglement advantage and separates this local advantage from advantage after global optimization over time. We exhibit examples in which the best unassisted strategy is approached only asymptotically, whereas an entangled probe achieves a strictly smaller error probability at finite time.

quant-ph↗

arXiv2025

Bayesian and Markovian classical feedforward for discriminating qubit channels

We address the issue of multishot discrimination between two qubit channels by invoking a simple adaptive protocol that employs Helstrom measurement at each step and classical information feedforward, beside separable inputs. We contrast the performance of Bayesian and Markovian strategies. We show that the former is only slightly advantageous and for a limited parameters' region.

quant-ph↗

arXiv2025

Discrimination of bosonic dephasing quantum channels

We study the possibility of discriminating between two bosonic dephasing quantum channels. We show that unambiguous discrimination is not realizable. We then consider discrimination with nonzero error probability and minimize this latter in the absence of input constraints. In the presence of an input energy constraint, we derive an upper bound on the error probability. Finally, we extend these results from single-shot to multi-shot discrimination, envisaging the asymptotic behavior.

quant-ph↗

arXiv2024

On the effectiveness of Bayesian discrete feedback for quantum information reclaiming

We consider discrete time feedback aimed at reclaiming quantum information after a channel action. We compare Bayesian and Markovian strategies. We show that the former does not offer any advantage for qubit channels, while its superior performance can appear in higher dimensional channels. This is witnessed by cases study for qutrit channels.

quant-ph↗

arXiv2023

Profitable entanglement for channel discrimination

We investigate the usefulness of side entanglement in discriminating between two generic qubit channels, {\ up to unitary pre- and post-processing,} and determine exact conditions under which it does enhance (as well as conditions under which it does not) the success probability. This is done in a constructive way by first analyzing the problem for channels that are extremal in the set of completely positive and trace-preserving qubit linear maps and then for channels that are inside such a set.

quant-ph↗

arXiv2023

Quantum reading of quantum information

We extend the notion of quantum reading to the case where the information to be retrieved, which is encoded into a set of quantum channels, is of quantum nature. We use two qubit unitaries describing the system environment interaction, with the initial environment state determining the system's input output channel and hence the encoded information. The performance of the most relevant two-qubit unitaries is determined with two different approaches: i) one-shot quantum capacity of the channel arising between environment and system's output; ii) estimation of parameters characterizing the initial quantum state of the environment. The obtained results are mostly in (qualitative) agreement, with some distinguishing features that include the CNOT unitary.

quant-ph↗

arXiv2022

Discrimination of dephasing channels

The problem of dephasing channel discrimination is addressed for finite-dimensional systems. In particular, the optimization with respect to input states without energy constraint is solved analytically for qubit, qutrit and ququart. Additionally, it is shown that resorting to side entanglement assisted strategy is completely useless in this case.

quant-ph↗

arXiv2021

Discriminating qubit amplitude damping channels

We address the issue of the discrimination between two-qubit amplitude damping channels by exploring several strategies. For the single-shot, we show that the excited state does not always give the optimal input, and that side entanglement assistance has limited benefit. On the contrary, feedback assistance from the environment is more beneficial. For the two-shot, we prove the in-utility of entangled inputs. Then focusing on individual (local) measurements, we find the optimal adaptive strategy.

quant-ph↗

arXiv2020

Quantum estimation through a bottleneck

We study the estimation of a single parameter characterizing families of unitary transformations acting on two systems. We consider the situation with the presence of bottleneck, i.e. only one of the systems can be measured to gather information. The estimation capabilities are related to unitaries' generators. In particular, we establish continuity of quantum Fisher information with respect to generators. Furthermore, we find conditions on the generators to achieve the same maximum quantum Fisher information we would have in the absence of bottleneck. We also discuss the usefulness of initial entanglement across the two systems as well as across multiple estimation instances.

quant-ph↗

arXiv2019

Adversarial vs cooperative quantum estimation

We address the estimation of a one-parameter family of isometries taking one input into two output systems. This primarily allows us to consider imperfect estimation by accessing only one output system, i.e. through a quantum channel. Then, on the one hand, we consider separate and adversarial control of the two output systems to introduce the concept of \emph{privacy of estimation}. On the other hand we conceive the possibility of separate but cooperative control of the two output systems. Optimal estimation strategies are found according to the minimum mean square error. This also implies the generalization of Personik's theorem to the case of local measurements. Finally, applications to two-qubit unitaries (with one qubit in a fixed input state) are discussed.

quant-ph↗

arXiv2018

The Volume of Two-Qubit States by Information Geometry

Using the information geometry approach, we determine the volume of the set of two-qubit states with maximally disordered subsystems. Particular attention is devoted to the behavior of the volume of sub-manifolds of separable and entangled states with fixed purity. We show that the usage of the classical Fisher metric on phase space probability representation of quantum states gives the same qualitative results with respect to different versions of the quantum Fisher metric.

math-ph↗

arXiv2017

Estimation of two-qubit interactions through channels with environment assistance

We consider the estimation of two-qubit interactions when initial states of both qubit can be locally controlled, while the final state of only one qubit can be measured. This amounts to realize a model of quantum channel communication with environment assistance. In such a framework the unitaries' parameters space results a tetrahedron in $\mathbb{R}^3$. On its edges the problem, becoming of single parameter estimation, can be exactly solved and we derive optimal probe states and estimators. Our results show that the possibility of environment assistance is always beneficial, while the usage of entanglement at channels' input is not.

quant-ph↗