Quantum Neural Network and Soft Quantum Computing

A new paradigm of quantum computing, namely, soft quantum computing, is proposed for nonclassical computation using real world quantum systems with naturally occurring environment-induced decoherence and dissipation. As a specific example of soft quantum computing, we suggest a quantum neural network, where the neurons connect pairwise via the "controlled Kraus operations", hoping to pave an easier and more realistic way to quantum artificial intelligence and even to better understanding certain functioning of the human brain. Our quantum neuron model mimics as much as possible the realistic neurons and meanwhile, uses quantum laws for processing information. The quantum features of the noisy neural network are uncovered by the presence of quantum discord and by non-commutability of quantum operations. We believe that our model puts quantum computing into a wider context and inspires the hope to build a soft quantum computer much earlier than the standard one.Comment: 5 pages, 1 figure; comments are welcom

Quantum Hall Effect under Rotation and Mass of the Laughlin Quasiparticles

We consider the quantum Hall effect induced by magnetic field and rotation, which can drive the Hall samples into the quantum Hall regime and induce fractional excitations. Both the mass and the charge of the Laughlin quasiparticles are predicted to be fractionally quantized. The observable effects induced by rotation are discussed. Based on the usual Hall samples under rotation, we propose an experimental setup for detecting the macroscopic quantization phenomena and the fractional mass of the Laughlin quasiparticles.Comment: 4 pages, 2 figures; comments are welcom

Unambiguous discrimination of extremely similar states by a weak measurement

In this paper, we propose a method to discriminate two extremely similar quantum states via a weak measurement. For the two states with equal prior probabilities, the optimum discrimination probability given by Ivanovic-Dieks-Peres limit can be achieved by our protocol with an appropriate choice of the interaction strength. However, compared with the conventional method for state discrimination, our approach shows the advantage of error-tolerance by achieving a better ratio of the success probability to the probability of error

Universal Entanglement and an Information-Complete Quantum Theory

The most challenging problem of modern physics is how to reconcile quantum theory and general relativity, namely, to find a consistent quantum theory in which gravity is quantized. This Progress Report focuses on such a tentative theory called the information-complete quantum theory (ICQT), in which (1) spacetime (gravity) as a physical quantum system plays a central role for formulating the theory, and (2) there are no any classical systems and concepts. Here universal spacetime-matter entanglement "glues" spacetime and matter (matter fermions and their gauge fields) as an indivisible trinity, encodes information-complete physical predictions of the world, and is as universal as universal gravitation. After summarizing the basic theoretic structure of the ICQT, conceptual advances achieved so far and some new issues within the ICQT are considered. While such a theory integrating quantum gravity is of fundamental interest to a wider audience, its relevance to quantum information technologies is discussed, with emphasis on its potential impacts on quantum computing and quantum communication.Comment: 35 pages. Comments are welcom

The information-complete quantum theory

Quantum mechanics is a cornerstone of our current understanding of nature and extremely successful in describing physics covering a huge range of scales. However, its interpretation remains controversial since the early days of quantum mechanics. What does a quantum state really mean? Is there any way out of the so-called quantum measurement problem? Here we present an information-complete quantum theory (ICQT) and the trinary property of nature to beat the above problems. We assume that a quantum system's state provides an information-complete description of the system in the trinary picture. We give a consistent formalism of quantum theory that makes the information-completeness explicitly and argue that conventional quantum mechanics is an approximation of the ICQT. We then show how our ICQT provides a coherent picture and fresh angle of some existing problems in physics. The computational content of our theory is uncovered by defining an information-complete quantum computer.Comment: 12 pages+1 figure; updated version; comments are welcom

Quantum Information Dynamics of Spacetime and Matter

It was known long ago that quantum theory and general relativity, two pillars of modern physics, are in sharp conflict in their foundations. Their fundamental inconsistencies render a consistent theory of quantum gravity the most challenging problem in physics. Here we propose an information-complete quantum field theory (ICQFT), which describes elementary fermions, their gauge fields, and gravity (together, called the trinary fields) as an elementary trinity without any conceptual inconsistency of existing theories. We then argue that the ICQFT provides a coherent picture and conceptual framework of unifying matter and spacetime (gravity) as information via spacetime-matter entanglement and gives a compelling solution to the problem of time and time's arrow. The trinary fields are characterized by dual entanglement and dual dynamics. Spacetime-matter entanglement encodes complete physical predictions of the theory and allows us to give a quantum information definition of dark energy. We consider two particular forms of spacetime-matter entangled states and their physical consequences. One of them\ is consistent with the variational holographic relation and another results in an universal relation between entanglement entropy and geometry (area and volume). This latter relation allows us to determine the cosmological constant term in the classical Einstein equation and implies that our Universe is not strictly holographic due to dark energy (related to an universal negative pressure). We predict the interior quantum state of a Schwarzschild black hole to be maximally information-complete. As a concrete quantum formulation of gravity coupled with matter, the ICQFT is about quantum information dynamics for spacetime and matter and eliminates the conceptual obstacles of existing quantum gravity theory.Comment: 17 pages, no figure; improved version. Comments are welcom

Practical Quantum Digital Signature

Guaranteeing nonrepudiation, unforgeability as well as transferability of a signature is one of the most vital safeguards in today's e-commerce era. Based on fundamental laws of quantum physics, quantum digital signature (QDS) aims to provide information-theoretic security for this cryptographic task. However, up to date, the previously proposed QDS protocols are impractical due to various challenging problems and most importantly, the requirement of authenticated (secure) quantum channels between participants. Here, we present the first quantum digital signature protocol that removes the assumption of authenticated quantum channels while remaining secure against the collective attacks. Besides, our QDS protocol can be practically implemented over more than 100 km under current mature technology as used in quantum key distribution.Comment: 13 pages 3 figure

Coupling-Deformed Pointer Observables and Weak Values

While the novel applications of weak values have recently attracted wide attention, weak measurement, the usual way to extract weak values, suffers from risky approximations and severe quantum noises. In this paper, we show that the weak-value information can be obtained exactly in strong measurement with postselections, via measuring the coupling-deformed pointer observables, i.e., the observables selected according to the coupling strength. With this approach, we keep all the advantages claimed by weak-measurement schemes and at the same time solve some widely criticized problems thereof, such as the questionable universality, systematical bias, and drastic inefficiency.Comment: 8 pages, 2 figure, accepted by Phys. Rev.

Rain Removal By Image Quasi-Sparsity Priors

Rain streaks will inevitably be captured by some outdoor vision systems, which lowers the image visual quality and also interferes various computer vision applications. We present a novel rain removal method in this paper, which consists of two steps, i.e., detection of rain streaks and reconstruction of the rain-removed image. An accurate detection of rain streaks determines the quality of the overall performance. To this end, we first detect rain streaks according to pixel intensities, motivated by the observation that rain streaks often possess higher intensities compared to other neighboring image structures. Some mis-detected locations are then refined through a morphological processing and the principal component analysis (PCA) such that only locations corresponding to real rain streaks are retained. In the second step, we separate image gradients into a background layer and a rain streak layer, thanks to the image quasi-sparsity prior, so that a rain image can be decomposed into a background layer and a rain layer. We validate the effectiveness of our method through quantitative and qualitative evaluations. We show that our method can remove rain (even for some relatively bright rain) from images robustly and outperforms some state-of-the-art rain removal algorithms.Comment: 12 pages, 12 figure

Quantum Uncertainty and Error-Disturbance Tradeoff

The uncertainty principle is often interpreted by the tradeoff between the error of a measurement and the consequential disturbance to the followed ones, which originated long ago from Heisenberg himself but now falls into reexamination and even heated debate. Here we show that the tradeoff is switched on or off by the quantum uncertainties of two involved non-commuting observables: if one is more certain than the other, there is no tradeoff; otherwise, they do have tradeoff and the Jensen-Shannon divergence gives it a good characterization.Comment: 8 pages, 2 figure