International Journal of Quantum Information

It is well known that quantum mechanics admits a geometric formulation on the complex projective space as a Kähler manifold. In this paper, we consider the notion of mutual information among continuous random variables in relation to the geometric description of a composite quantum system introducing a new measure of total correlations that can be computed in terms of Gaussian integrals.

Recently, a novel quantum-key-distribution (QKD) protocol, called Round-robin-differential-phase-shift (RRDPS) QKD, has been proposed to share a secure key without monitoring the signal disturbance. In this paper, we propose a decoy state RRDPS-QKD protocol with odd coherent states (OCS). We implement a one-intensity decoy state method into the RRDPS-QKD with OCS to estimate the key rate. The results show that both the maximum transmission distance and the key rate of our protocol are significantly improved. Moreover, only one-intensity decoy state is sufficient for the protocol to approach the asymptotic limit with infinite decoy states.

In the process of quantum key distribution (QKD), error correction algorithm is used to correct the error bits of the key at both ends. The existing applied QKD system has a low key rate and is generally Kbps of magnitude. Therefore, the performance requirement of data processing such as error correction is not high. In order to cope with the development demand of high-speed QKD system in the future, this paper introduces the Winnow algorithm to realize high-speed parity and hamming error correction based on Field Programmable Gate Array (FPGA), and explores the performance limit of this algorithm. FPGA hardware implementation can achieve the scale of Mbps bandwidth, with choosing different group length of sifted key by different error rate, and can achieve higher error correction efficiency by reducing the information leakage in the process of error correction, and improves the QKD system’s secure key rate, thus helping the future high-speed QKD system.

We research the input–output process with nitrogen-vacancy (NV) centers fixed on the surface of micro-toroidal resonators (MTRs) with whispering-gallery modes (WGMs) and then present an efficient scheme for the synchronized generation of Bell and W states. In our scheme, entanglement can be prepared with the assistance of the polarized photon pulse and electron spin state of NV center. The analysis of the efficiency shows that our scheme is feasible with the current technology, which can be further used for quantum information processing.

In this paper [J. Sun, S. Lu and F. Liu, Open Syst. Info. Dyn.23(3) (2016) 1650016], we have studied a general class of adiabatic evolutions in quantum adiabatic search type problem, and found another limitation on it, besides those reported in our early work. In this paper, we extend this study by considering adding an extra driving scheme to the system Hamiltonian of this type of quantum adiabatic evolution. It will be shown that, like the previous study in [J. Sun, S. Lu and F. Liu, Open Syst. Info. Dyn.23(3) (2016) 1650016], the limitation above can also possibly penetrate into the search type quantum-adiabatic computation even by this more general family of system Hamiltonian, which may shed light on what we should have in mind when solving practical problems by means of quantum adiabatic evolution.

Traditional machine learning shares several benefits with quantum information processing field. The study of machine learning with quantum mechanics is called quantum machine learning. Data clustering is an important tool for machine learning where quantum computing plays a vital role in its inherent speed up capability. In this paper, a hybrid quantum algorithm for data clustering (quantum walk-based hybrid clustering (QWBHC)) is introduced where one-dimensional discrete time quantum walks (DTQW) play the central role to update the positions of data points according to their probability distributions. A quantum oracle is also designed and it is mainly implemented on a finite $d$-regular bipartite graph where data points are initially distributed as a predefined set of clusters. An overview of a quantum walk (QW) based clustering algorithm on 1D lattice structure is also introduced and described in this paper. In order to search the nearest neighbors, a unitary and reversible DTQW gives a quadratic speed up over the traditional classical random walk. This paper also demonstrates the comparisons of our proposed hybrid quantum clustering algorithm with some state-of-the-art clustering algorithms in terms of clustering accuracy and time complexity analysis. The proposed quantum oracle needs $O(\sqrt{n})$ queries to mark the nearest data points among clusters and modify the existing clusters. Finally, the proposed QWBHC algorithm achieves $O(n)+O(\sqrt{n})$ performance.

We introduce a new method to compute the Quantum Geometric Tensor, this procedure allows us to compute the Quantum Information Metric and the Berry curvature perturbatively for a theory with an arbitrary interaction Hamiltonian. The calculation uses the generating function method, and it is illustrated with the harmonic oscillator with a linear and a quartic perturbation.

This work is at the interface of graph theory and quantum mechanics. Quantum correlations epitomize the usefulness of quantum mechanics. Quantum discord is an interesting facet of bipartite quantum correlations. Earlier, it was shown that every combinatorial graph corresponds to quantum states whose characteristics are reflected in the structure of the underlined graph. A number of combinatorial relations between quantum discord and simple graphs were studied. To extend the scope of these studies, we need to generalize the earlier concepts applicable to simple graphs to weighted graphs, corresponding to a diverse class of quantum states. To this effect, we determine the class of quantum states whose density matrix representation can be derived from graph Laplacian matrices associated with a weighted directed graph and call them graph Laplacian quantum states. We find the graph theoretic conditions for zero and nonzero quantum discord for these states. We apply these results on some important pure two qubit states, as well as a number of mixed quantum states, such as the Werner, Isotropic, and $X$-states. We also consider graph Laplacian states corresponding to simple graphs as a special case.

We propose to utilize the Bose–Einstein condensate (BEC) for precision phase sensitive measurement of position and momentum displacements. The controlled two-soliton dynamics can be turned into a quantum probe to measure these parameters with high precision in an experimentally verified system of bright solitary trains. A careful phase space analysis of the dynamics of the mesoscopic wave packet is carried out through Wigner phase space picture for finding out the parameter domain exhibiting sub-Planck structures, required for precision quantum metrology. We propose two experimentally feasible scenarios, one involving the overall phase and the other through the relative phase between the two-solitons when they are oscillating inside the trap. In both the cases, detailed analytical studies are carried out through the overlap functions which reveal the sensitivity issue. A careful analysis is also performed to find the parametric domain relevant for the use of BEC for weak value estimation.

This paper points out a security loophole in the Quantum key distribution with limited classical Bob [Int. J. Quantum Inf. 11(01) (2013) 1350005]. With the loophole, an eavesdropper can perform the double CNOT attack to reveal about $n∕4$-bits out of an $n$-bit key without being detected by the protocol.