Experimental realization of quantum cheque using a five-qubit quantum computer

Quantum cheques could be a forgery-free way to make transaction in a quantum networked banking system with perfect security against any no-signalling adversary. Here, we demonstrate the implementation of quantum cheque, proposed by Moulick and Panigrahi (Quantum Inf Process 15:2475–2486, 2016), using the five-qubit IBM quantum computer. Appropriate single qubit, CNOT and Fredkin gates are used in an optimized configuration. The accuracy of implementation is checked and verified through quantum state tomography by comparing results from the theoretical and experimental density matrices.     

Toward quantum computation: a five-qubit quantum processor

Quantum physics presents intriguing possibilities for achieving computational gains after conventional miniaturization reaches its limits. Accordingly, we describe a nuclear magnetic-resonance quantum computer demonstrating a quantum algorithm that exponentially outperforms classical algorithms     

Bidirectional controlled quantum teleportation and secure direct communication using five-qubit entangled state

A scheme is presented to implement bidirectional controlled quantum teleportation (QT) by using a five-qubit entangled state as a quantum channel, where Alice may transmit an arbitrary single qubit state called qubit A to Bob and at the same time, Bob may also transmit an arbitrary single qubit state called qubit B to Alice via the control of the supervisor Charlie. Based on our channel, we explicitly show how the bidirectional controlled QT protocol works. By using this bidirectional controlled teleportation, espcially, a bidirectional controlled quantum secure direct communication (QSDC) protocol, i.e., the so-called controlled quantum dialogue, is further investigated. Under the situation of insuring the security of the quantum channel, Alice (Bob) encodes a secret message directly on a sequence of qubit states and transmits them to Bob (Alice) supervised by Charlie. Especially, the qubits carrying the secret message do not need to be transmitted in quantum channel. At last, we show this QSDC scheme may be determinate and secure.     

Constructing quantum logic gates using q-deformed harmonic oscillator algebras

We study two-level q-deformed angular momentum states, and using q-deformed harmonic oscillators, we provide a framework for constructing qubits and quantum gates. We also present the construction of some basic one-qubit and two-qubit quantum logic gates.     

基于IBM量子计算云服务的量子傅里叶变换实现

Shor算法能够相对经典大整数分解算法实现指数加速,从而直接威胁到了RSA密码体制,而量子傅里叶变换是Shor算法中的一个关键变换,也能够相对经典离散傅里叶变换实现指数加速,从而引起了广泛关注。主要针对量子傅里叶变换的实现方案进行研究。首先介绍了IBM公司量子计算云服务的编程基础,随后设计了3比特量子傅里叶变换的量子线路,最后在IBM公司5超导量子比特的量子计算芯片上进行了实验验证。     

Schemes for teleportation of quantum gates

Quantum teleportation is a computational primitive that allows non-local quantum communication and quantum computation. In this work, we present two schemes for quantum gate teleportation. The first scheme shows under what conditions an n-qudit gate can be teleported using a generalization of Gottesman-Chuang procedure [Nature 402, 390 (1999)]. The second scheme shows that quantum gate teleportation can be transformed in the teleportation of a single-qudit.     

参数化的广义量子通用相位门

主要研究参数化的广义量子通用相位门,给出了单比特量子门、双比特量子门以及三比特量子门的参数化构造。证明参数化的广义量子门和M.Nielsen给出的广义量子门是等价的。举例说明了参数化的广义量子通用门在量子计算中的作用。     

Finding the chromatic sums of graphs using a D-Wave quantum computer

The Journal of Supercomputing - In this paper we demonstrate how to solve the chromatic sum problem using a D-Wave quantum computer. Starting from a BIP (binary integer programming) formulation, we...     

Simulating fermions on a quantum computer

The real-time probabilistic simulation of quantum systems in classical computers is known to be limited by the so-called dynamical sign problem, a problem leading to exponential complexity. In 1981 Richard Feynman raised some provocative questions in connection to the “exact imitation” of such systems using a special device named a “quantum computer”. Feynman hesitated about the possibility of imitating fermion systems using such a device. Here we address some of his concerns and, in particular, investigate the simulation of fermionic systems. We show how quantum computers avoid the sign problem in some cases by reducing the complexity from exponential to polynomial. Our demonstration is based upon the use of isomorphisms of algebras. We present specific quantum algorithms that illustrate the main points of our algebraic approach.     

Theoretical comparison of quantum Zeno gates and logic gates based on the cross-Kerr nonlinearity

Quantum logic operations can be implemented using nonlinear phase shifts (the Kerr effect) or the quantum Zeno effect based on strong two-photon absorption. Both approaches utilize three-level atoms, where the upper level is tuned on resonance for the Zeno gates and off-resonance for the nonlinear phase gates. The performance of nonlinear phase gates and Zeno gates are compared under conditions where the parameters of the resonant cavities and three-level atoms are the same in both cases. It is found that the expected performance is comparable for the two approaches despite the fundamental differences between the Zeno and Kerr effects.     

A quantum full adder for a scalable nuclear spin quantum computer

We demonstrate a strategy for implementation a quantum full adder in a spin chain quantum computer. As an example, we simulate a quantum full adder in a chain containing 201 spins. Our simulations also demonstrate how one can minimize errors generated by non-resonant effects.     

Quantum information splitting of an arbitrary three-qubit state by using a genuinely entangled five-qubit state and a Bell-state

A new application of the genuinely entangled five-qubit state introduced by Brown et al. (J Phys A 38(5), 1119–1131, 2005) is investigated for quantum information splitting (QIS) of an arbitrary three-qubit state. We demonstrate that such a genuine five-qubit entangled state and a Bell-state can be used to realize the deterministic QIS of an arbitrary three-qubit state by performing the Bell-state measurements and single qubit measurement. The presented protocol is showed to be secure against certain eavesdropping attacks.     

Direct implementation of an N-qubit controlled-unitary gate in a single step

We present a new scheme to implement an N-qubit controlled-unitary operation directly in a single step. The main advantage of our scheme is that we do not use conventional gate decomposition protocols to break an N-qubit controlled-unitary gate into one- and two-qubit gates. This greatly reduces the number of computational steps in implementing quantum algorithms and error-correcting codes, which use multi-control unitary operations. We show how to find analytic solutions to the time evolution of the system, so that system parameters can be found to realize the desired N-qubit controlled-unitary operations.     

Scalable digital hardware for a trapped ion quantum computer

Quantum Information Processing - Many of the challenges of scaling quantum computer hardware lie at the interface between the qubits and the classical control signals used to manipulate them....     

Efficient experimental design of high-fidelity three-qubit quantum gates via genetic programming

We have designed efficient quantum circuits for the three-qubit Toffoli (controlled–controlled-NOT) and the Fredkin (controlled-SWAP) gate, optimized via genetic programming methods. The gates thus obtained were experimentally implemented on a three-qubit NMR quantum information processor, with a high fidelity. Toffoli and Fredkin gates in conjunction with the single-qubit Hadamard gates form a universal gate set for quantum computing and are an essential component of several quantum algorithms. Genetic algorithms are stochastic search algorithms based on the logic of natural selection and biological genetics and have been widely used for quantum information processing applications. We devised a new selection mechanism within the genetic algorithm framework to select individuals from a population. We call this mechanism the “Luck-Choose” mechanism and were able to achieve faster convergence to a solution using this mechanism, as compared to existing selection mechanisms. The optimization was performed under the constraint that the experimentally implemented pulses are of short duration and can be implemented with high fidelity. We demonstrate the advantage of our pulse sequences by comparing our results with existing experimental schemes and other numerical optimization methods.     

Electrocardiomultigraphimeter using a home computer

The drop in hardware costs has fostered the widespread use of home-computer systems. Because of this situation, the home computer can be profitably employed in some highly specialized fields. We believe electrocardiographic instrumentation to be one such field. We have built an electrocardiomultigraphimeter (ECXGM), which can be considered as a development of the traditional electrocardiograph that performs some additional functions. Our prototype features vectorcardiography, polar coordinate tracing, automatic measurements between fiducial points selected by the user with a joystick and screen cursor and trace filing by patient on labelled floppy disks. The standard hardware consists of a Commodore 64 console, a monitor, two floppy disk drives and an Epson HI-80 plotter, all of which are readily available. The special hardware consists of an A/D converter, which receives the electrocardiographic signal downstream of the amplifying stage, which is a standard feature of any electrocardiograph. Prototype development mostly involved the software. Difficulties were posed by the limited resources available on home computers, an important point in view of the problem to be tackled. The solutions adopted are based on the use of assembler language and overloading techniques and minimizing the interconnections among the software modules defined in a compactly built program. The result is an instrument with significantly advanced clinico-scientific capabilities as compared to current electrocardiographic instruments. This fact, and the class of the hardware used and special software built, confer originality to this work. The new instrument ought to be especially suitable for the offices of cardiologists who have an interest in such capabilities, and for schools of electrocardiography.     

Electrocardiogram simulation using a personal computer

A personal computer with a digital-to-analog converter is used as an electrocardiogram simulator. A TurboPascal procedure, given the heart rate, rhythm, and ST segment levels, generates the voltages for Leads II and V5. A simple circuit reduces the voltages to the physiologic range and smoothes the waveforms, removing the staircase effects of digitalization. The procedure can be manually controlled using a software interface or driven by other programs for use in a full-scale operating room simulator.     

Spatial conferencing using a wearable computer

Wearable computers provide constant access to computing and communications resources; however, there are many unanswered questions as to how this computing power can be used to enhance communication. We describe a wearable augmented reality communication space that uses spatialised 3D graphics and audio cues to aid communication. The user is surrounded by virtual avatars of the remote collaborators that they can interact with using natural head and body motions. The use of spatial cues means that the conferencing space can potentially support dozens of simultaneous users. We report on two experiments that show users can understand speakers better with spatial rather than non-spatial audio, and that minimal visual cues may be sufficient to distinguish between speakers. Additional informal user studies with real conference participants suggest that wearable communication spaces may offer significant advantages over traditional communication devices.     

Realization of multiple-input basic logic gates using microprocessors

The possibility of performing various basic logic operations (e.g. OR and AND) on multiple-input gates using a microprocessor is investigated. This work may be useful in simulating logic circuits is software without going into the hardware implementation.     

Experimental demonstration of reset control design

Using the describing function method, engineers in the 1950s and 1960s conceived of novel nonlinear compensators in an attempt to overcome performance limitations inherent in linear time-invariant (LTI) control systems. This paper is concerned with a subset of such devices called “reset controllers”, which are LTI systems equipped with mechanisms and laws to reset their states to zero. This paper reports on a design procedure and a laboratory experiment, the first to be reported in the literature, in which the resulting reset controller provides better design tradeoffs than LTI compensation. Specifically, it is shown that reset control increases the level of sensor-noise suppression without sacrificing either disturbance-rejection performance or gain/phase margins.