Experimental demonstration of quantum entanglement among more than two quantum systems with continuous spectra is summarized in the paper. The tripartite entangled state, named also GHZ-like state, is produced by dist...
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ISBN:
(纸本)0780377338
Experimental demonstration of quantum entanglement among more than two quantum systems with continuous spectra is summarized in the paper. The tripartite entangled state, named also GHZ-like state, is produced by distributing a two-mode squeezed state light to three parties using beamsplitter. A nondegenerate optical parameter amplifier (NOPA) operating at deamplification serves as the initial bipartite entanglement source. The output optical modes from the NOPA are a pair of bright EPR entangled beams with orthogonal polarizations, anticorrelated amplitude quadratures and correlated phase quadratures. The results confirm the existence of the quantum correlation among three amplitude quadratures of modes.
We consider how randomness can be made to play a useful role in quantuminformationprocessing-in particular, for decoherence control and the implementation of quantumalgorithms. For a two-level system in which the d...
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We consider how randomness can be made to play a useful role in quantuminformationprocessing-in particular, for decoherence control and the implementation of quantumalgorithms. For a two-level system in which the decoherence channel is non-dissipative, we show that decoherence suppression is possible if memory is present in the channel. Random switching between two potentially harmful noise sources can then provide a source of stochastic control. Such random switching can also be used in an advantageous way for the implementation of quantumalgorithms. (C) 2002 Elsevier Science B.V. All rights reserved.
We investigate distinguishability (measured by fidelity) of the initial and the final state of a qubit, which is an object of the so-called nonideal quantum measurement of the first kind. We show that the fidelity of ...
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We investigate distinguishability (measured by fidelity) of the initial and the final state of a qubit, which is an object of the so-called nonideal quantum measurement of the first kind. We show that the fidelity of a nonideal measurement can be greater than the fidelity of the corresponding ideal measurement. This result is somewhat counterintuitive, and can be traced back to the quantum parallelism in quantum operations, in analogy with the quantum parallelism manifested in the quantum computing theory. In particular, as the quantum parallelism in quantum computing underlies efficient quantumalgorithms, the quantum parallelism in quantuminformation theory underlies the classically unexpected increase of fidelity.
Experimental realization of quantuminformationprocessing in the field of nuclear magnetic resonance (NMR) has been well established. Implementation of conditional phase-shift gate has been a significant step, which ...
Experimental realization of quantuminformationprocessing in the field of nuclear magnetic resonance (NMR) has been well established. Implementation of conditional phase-shift gate has been a significant step, which has lead to realization of important algorithms such as Grover's search algorithm and quantum Fourier transform. This gate has so far been implemented in NMR by using coupling evolution method. We demonstrate here the implementation of the conditional phase-shift gate using transition selective pulses. As an application of the gate, we demonstrate Grover's search algorithm and quantum Fourier transform by simulations and experiments using transition selective pulses. (C) 2002 Elsevier Science (USA). All rights reserved.
In this article we present a signal processing framework that we refer to as quantum signal processing (QSP) (Eldar 2001) that is aimed at developing new or modifying existing signal processingalgorithms by borrowing...
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In this article we present a signal processing framework that we refer to as quantum signal processing (QSP) (Eldar 2001) that is aimed at developing new or modifying existing signal processingalgorithms by borrowing from the principles of quantum mechanics and some of its interesting axioms and constraints. However, in contrast to such fields as quantum computing and quantuminformation theory, it does not inherently depend on the physics associated with quantum mechanics. Consequently, in developing the QSP framework we are free to impose quantum mechanical constraints that we find useful and to avoid those that are not. This framework provides a unifying conceptual structure for a variety of traditional processing techniques and a precise mathematical setting for developing generalizations and extensions of algorithms, leading to a potentially useful paradigm for signal processing with applications in areas including frame theory, quantization and sampling methods, detection, parameter estimation, covariance shaping, and multiuser wireless communication systems. We present a general overview of the key elements in quantum physics that provide the basis for the QSP framework and an indication of the key results that have so far been developed within this framework. In the remainder of the article, we elaborate on the various elements in this figure.
The advantages of using quantum systems for performing many computational tasks have already been established. Several quantumalgorithms have been developed which exploit the inherent property of quantum systems such...
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The advantages of using quantum systems for performing many computational tasks have already been established. Several quantumalgorithms have been developed which exploit the inherent property of quantum systems such as superposition of states and entanglement for efficiently performing certain tasks. The experimental implementation has been achieved on many quantum systems, of which nuclear magnetic resonance has shown the largest progress in terms of number of qubits. This paper describes the use of a spin-7/2 as a three-qubit system and experimentally implements the half-adder and subtractor operations. The required qubits are realized by partially orienting 133Cs nuclei in a liquid-crystalline medium, yielding a quadrupolar split well-resolved septet. Another feature of this paper is the proposal that labeling of quantum states of system can be suitably chosen to increase the efficiency of a computational task.
We consider the problem of identifying a base k string given an oracle which returns information about the number of correct components in a query, specifically, the Hamming distance between the query and the solution...
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We consider the problem of identifying a base k string given an oracle which returns information about the number of correct components in a query, specifically, the Hamming distance between the query and the solution, modulo r = max{2, 6 - k}. Classically this problem requires Omega(n log(r) k) queries. For k is an element of {2, 3, 4}, we construct quantumalgorithms requiring only a single quantum query. For k > 4, we show that O(root k) quantum queries suffice. In both cases the quantumalgorithms are optimal.
A quantum computer directly manipulates information stored in the state of quantum mechanical systems. The available operations have many attractive features but also underly severe restrictions, which complicate the ...
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ISBN:
(纸本)0819444073
A quantum computer directly manipulates information stored in the state of quantum mechanical systems. The available operations have many attractive features but also underly severe restrictions, which complicate the design of quantumalgorithms. We present a divide-and-conquer approach to the design of various quantumalgorithms. The class of algorithm includes many transforms which are well-known in classical signal processing applications. We show how fast quantumalgorithms can be derived for the discrete Fourier transform, the Walsh-Hadamard transform, the Slant transform, and the Hartley transform. All these algorithms use at most O(log(2) N) operations to transform a state vector of a quantum computer of length N.
We prove that majorization relations hold step by step in the quantum Fourier Transformation (QFT) for phase-estimation algorithms. Our result relies on the fact that states which are mixed by Hadamard operators at an...
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We prove that majorization relations hold step by step in the quantum Fourier Transformation (QFT) for phase-estimation algorithms. Our result relies on the fact that states which are mixed by Hadamard operators at any stage of the computation only differ by a phase. This property is a consequence of the structure of the initial state and of the QFT, based on controlled-phase operators and a single action of a Hadamard gate per qubit. The detail of our proof shows that Hadamard gates sort the probability distribution associated to the quantum state, whereas controlled-phase operators carry all the entanglement but are immaterial to majorization. We also prove that majorization in phase-estimation algorithms follows in a most natural way from unitary evolution, unlike its counterpart in Grover's algorithm.
I review and expand the model of quantum associative memory that I have recently proposed. In this model binary patterns of n bits are stored in the quantum superposition of the appropriate subset of the computational...
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I review and expand the model of quantum associative memory that I have recently proposed. In this model binary patterns of n bits are stored in the quantum superposition of the appropriate subset of the computational basis of n qbits. information can be retrieved by performing an input-dependent rotation of the memory quantum state within this subset and measuring the resulting state. The amplitudes of this rotated memory state are peaked on those stored patterns which are closest in Hamming distance to the input, resulting in a high probability of measuring a memory pattern very similar to it. The accuracy of pattern recall can be tuned by adjusting a parameter playing the role of an effective temperature. This model solves the well-known capacity shortage problem of classical associative memories, providing a large improvement in capacity.
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