International Journal of Quantum Information

Quantum computation has emerged in the past decades as a consequence of down-scaling of electronic devices to the mesoscopic regime and of advances in the ability of controlling and measuring microscopic quantum systems. Quantum computation has many interdisciplinary aspects, ranging from physics and chemistry to mathematics and computer science. In this paper, we focus on physical hardware, present day challenges and future directions for design of quantum architectures.

A brief introduction to quantum information theory in the context of quantum optics is presented. After presenting the fundamental theoretical basis of the subject, experimental evaluation of entanglement measures are discussed, followed by applications to communication and imaging.

In this paper, we construct two classes of new quantum maximum-distance-separable (MDS) codes with parameters , where q is an odd prime power with q ≡ 3 (mod 4) and ; [[8(q - 1), 8(q - 1) - 2d + 2, d]]_q, where q is an odd prime power with the form q = 8t - 1 (t is an even positive integer) and . Comparing the parameters with all known quantum MDS codes, the quantum MDS codes exhibited here have minimum distances bigger than the ones available in the literature.

This paper considers the construction of quantum error correcting codes from linear codes over finite commutative Frobenius rings. We extend the Calderbank–Shor–Steane (CSS) construction to these rings. Further, quantum codes are extended to matrix product codes. Quantum codes over 𝔽_p^k are also obtained from linear codes over rings using the generalized Gray map.

The mixing process of discrete-time quantum walks on one-dimensional lattices is revisited in a setting where the walker is coupled to an environment, and the time evolution of the walker and the environment is unitary. The mixing process is found to be incomplete, in the sense that the walker does not approach the maximally mixed state indefinitely, but the distance to the maximally mixed state saturates to some finite value depending on the size of the environment. The quantum speedup of mixing time is investigated numerically as the size of the environment decreases from infinity to a finite value. The mixing process in this unitary setting can be explained by interpreting it as an equilibration process in a closed quantum system, where subsystems can exhibit equilibration even when the entropy of the total system remains zero.

A fractal medium is defined and its computational properties (bistability, reproduction itself, capacity to memorize, self-similarity, polarization, information communication, etc.) are presented and argued. As it is well known, the quantum medium is the base of the theoretical fundamentation of the quantum computer. We prove that the fractal medium is an extension of the quantum medium. Hence, the fractal computer can be defined as generalization of the quantum computer.

In this work, we propose a complete design of a quantum relational multi-tables database. We illustrate how to perform basic and advanced queries to insert, update, delete and select records from single or joined digitized tables. A suggestion of a Quantum Query Language (QQL) is then addressed and we illustrate for a simple quantum database how QQL performs. We highlight the used scheme allowing to traduce the QQL semantics to the corresponding CNOT-based implementation and we underline the evolution of the amplitude of probability of the superposed states contained in the tables.

We analyze an optomechanical system formed by a mechanical mode and the two optical modes of an optomechanical cavity for the realization of a strongly quantum correlated three-mode system. We show that the steady state of the system shows three possible bipartite continuous variable (CV) entanglements in an experimentally accessible parameter regime, which are robust against temperature. We further show that selective entanglement between the mechanical mode and any of the two optical modes is also possible by the proper choice of the system parameters. Such a two-mode optomechanical system can be used for the realization of CV quantum information interfaces and networks.