scholarly journals Robust Phase Estimation of Gaussian States in the Presence of Outlier Quantum States

2020 ◽  
Vol 10 (16) ◽  
pp. 5475
Author(s):  
Yukito Mototake ◽  
Jun Suzuki
Keyword(s):  
Coherent State ◽  
Quantum System ◽  
Robust Statistics ◽  
Quantum States ◽  
Phase Estimation ◽  
Gaussian States ◽  
Statistical Framework

In this paper, we investigate the problem of estimating the phase of a coherent state in the presence of unavoidable noisy quantum states. These unwarranted quantum states are represented by outlier quantum states in this study. We first present a statistical framework of robust statistics in a quantum system to handle outlier quantum states. We then apply the method of M-estimators to suppress untrusted measurement outcomes due to outlier quantum states. Our proposal has the advantage over the classical methods in being systematic, easy to implement, and robust against occurrence of noisy states.

Proposal for dimensionality testing in QPQ

2018 ◽  
Vol 18 (13&14) ◽  
pp. 1125-1142
Author(s):  
Arpita Maitra ◽  
Bibhas Adhikari ◽  
Satyabrata Adhikari
Keyword(s):  
Information Processing ◽  
Quantum Information ◽  
Quantum System ◽  
Quantum State ◽  
Quantum Information Processing ◽  
Quantum States ◽  
Quantum Private Query ◽  
Unfair Advantage ◽  
Security Proofs

Recently, dimensionality testing of a quantum state has received extensive attention (Ac{\'i}n et al. Phys. Rev. Letts. 2006, Scarani et al. Phys. Rev. Letts. 2006). Security proofs of existing quantum information processing protocols rely on the assumption about the dimension of quantum states in which logical bits are encoded. However, removing such assumption may cause security loophole. In the present paper, we show that this is indeed the case. We choose two players' quantum private query protocol by Yang et al. (Quant. Inf. Process. 2014) as an example and show how one player can gain an unfair advantage by changing the dimension of subsystem of a shared quantum system. To resist such attack we propose dimensionality testing in a different way. Our proposal is based on CHSH like game. As we exploit CHSH like game, it can be used to test if the states are product states for which the protocol becomes completely vulnerable.

Sub- and super-fidelity as bounds for quantum fidelity

2009 ◽  
Vol 9 (1&2) ◽  
pp. 103-130
Author(s):  
J.A. Miszczak ◽  
Z. Puchala ◽  
P. Horodecki ◽  
A. Uhlmann ◽  
K. Zyczkowski
Keyword(s):  
Quantum System ◽  
Quantum States ◽  
Concave Functions ◽  
Two Dimensional ◽  
Quantum Fidelity

We derive several bounds on fidelity between quantum states. In particular we show that fidelity is bounded from above by a simple to compute quantity we call super--fidelity. It is analogous to another quantity called sub--fidelity. For any two states of a two--dimensional quantum system (N=2) all three quantities coincide. We demonstrate that sub-- and super--fidelity are concave functions. We also show that super--fidelity is super--multiplicative while sub--fidelity is sub--multiplicative and design feasible schemes to measure these quantities in an experiment.Super--fidelity can be used to define a distance between quantum states. With respect to this metric the set of quantum states forms a part of a N^2-1 dimensional hypersphere.

scholarly journals Probing Rényi entanglement entropy via randomized measurements

Science ◽  
2019 ◽  
Vol 364 (6437) ◽  
pp. 260-263 ◽  
Author(s):  
Tiff Brydges ◽  
Andreas Elben ◽  
Petar Jurcevic ◽  
Benoît Vermersch ◽  
Christine Maier ◽  
...  
Keyword(s):  
Quantum System ◽  
Entanglement Entropy ◽  
Quantum Systems ◽  
Quantum States ◽  
Many Body ◽  
Trapped Ion ◽  
Statistical Correlations ◽  
Quantum Simulator ◽  
Entanglement Structure ◽  
Arbitrary Quantum

Entanglement is a key feature of many-body quantum systems. Measuring the entropy of different partitions of a quantum system provides a way to probe its entanglement structure. Here, we present and experimentally demonstrate a protocol for measuring the second-order Rényi entropy based on statistical correlations between randomized measurements. Our experiments, carried out with a trapped-ion quantum simulator with partition sizes of up to 10 qubits, prove the overall coherent character of the system dynamics and reveal the growth of entanglement between its parts, in both the absence and presence of disorder. Our protocol represents a universal tool for probing and characterizing engineered quantum systems in the laboratory, which is applicable to arbitrary quantum states of up to several tens of qubits.

Quantum states of extended objects beyond the coherent state approximation

1977 ◽  
Vol 118 (5) ◽  
pp. 371-380 ◽  
Author(s):  
Jürgen Baacke ◽  
Heinz J. Rothe
Keyword(s):  
Coherent State ◽  
Quantum States ◽  
State Approximation

scholarly journals Optical phase estimation via the coherent state and displaced-photon counting

2016 ◽  
Vol 94 (3) ◽  
Author(s):  
Shuro Izumi ◽  
Masahiro Takeoka ◽  
Kentaro Wakui ◽  
Mikio Fujiwara ◽  
Kazuhiro Ema ◽  
...  
Keyword(s):  
Coherent State ◽  
Photon Counting ◽  
Phase Estimation ◽  
Optical Phase

scholarly journals Partial traces and the geometry of entanglement: Sufficient conditions for the separability of Gaussian states

2021 ◽  
Author(s):  
Nuno Costa Dias ◽  
Maurice de Gosson ◽  
João Nuno Prata
Keyword(s):  
Density Operator ◽  
Sufficient Conditions ◽  
Quantum States ◽  
Partial Trace ◽  
Gaussian States ◽  
Geometrical Properties ◽  
Partial Transposition

The notion of partial trace of a density operator is essential for the understanding of the entanglement and separability properties of quantum states. In this paper, we investigate these notions putting an emphasis on the geometrical properties of the covariance ellipsoids of the reduced states. We thereafter focus on Gaussian states and we give new and easily numerically implementable sufficient conditions for the separability of all Gaussian states. Unlike the positive partial transposition criterion, none of these conditions is however necessary.

Sign in / Sign up

Export Citation Format

Share Document