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arXiv:quant-ph/0202146

Experimental study of quantum decoherence using nuclear magnetic resonance

Jingfu Zhang, Zhi-Heng Lu, Shan Lu, Zhiwei Deng

Published Feb 26, 2002• 1 citation
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Abstract

Quantum decoherence has been studied using nuclear magnetic resonance(NMR). By choosing one qubit to simulate environment, we examine the decoherence behavior of two quantum systems: a one qubit system and a two qubit system. The experimental results show agreements with the theoretical predictions. Our experiment schemes can be generalized to the case that the environment is composed of multiple qubits.

DOI
10.48550/arxiv.quant-ph/0202146

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Quantum decoherence has been studied using nuclear magnetic resonance(NMR). By choosing one qubit to simulate environment, we examine the decoherence behavior of two quantum systems: a one qubit system and a two qubit system. The experimental results show agreements with the theoretical predictions. Our experiment schemes can be generalized to the case that the environment is composed of multiple qubits.
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"We review the theoretical and the experimental researches aimed at quantifying or identifying quantum correlations in liquid-state nuclear magnetic resonance (NMR) systems at room temperature. We first overview, at the formal level, a method to determine the quantum discord and its classical counterpart in systems described by a deviation matrix. Next, we describe an experimental implementation of that method. Previous theoretical analysis of quantum discord decoherence had predicted the time dependence of the discord to change suddenly under the influence of phase noise. The experiment attests to the robustness of the effect, sufficient to confirm the theoretical prediction even under the additional influence of a thermal environment. Finally, we discuss an observable witness for the quantumness of correlations in two-qubit systems and its first NMR implementation. Should the nature, not the amount, of the correlation be under scrutiny, the witness offers the most attractive alternative."
This paper presents our theoretical and nuclear magnetic resonance(NMR) experimental work on several QIPs including quantum super dense coding(QSDC),quantum algorithms,quantum error correction,and decoherence-free subspace.The main contents are,(1) Using NMR technique,we realize two kinds of QSDC.The experimental results show that QSDC only needs to transfer(N-1) qubits during transmitting N bits classical information;(2) On NMR quantum computers,we realize three kinds of quantum algorithms that include four-qubit summing algorithm,four-qubit Deutsch-like algorithm and seven-qubit Deutsch-Jozsa algorithm;(3) We present a quantum error correction scheme based on quantum cloning.This scheme shows the relationship between quantum cloning and quantum error correction;(4) To avoid decoherence in quantum algorithms,we construct a decoherence-free subspace(DFS) by using multiple quantum coherences.The validity of this DFS is also experimentally verified on our NMR quantum computers.The DFS makes the three unaddressed protons in a CH_3 group distinguished in two-dimensional(2D) NMR.It can protect against more error operators.This idea may provide new insights into extending the number of qubits in the sense that it effectively utilizes the magnetically equivalent nuclei.
This Letter presents a two-dimensional nuclear magnetic resonance (NMR) approach for constructing a two-logical-qubit decoherence-free subspace (DFS) by using four multiple-quantum coherences of a CH3 spin system as logical qubits. The three protons in this spin system are magnetically equivalent and can only be used as a single qubit in one-dimensional NMR. We have experimentally demonstrated that our DFS can protect against more types of decoherences than those of the one composed of four noisy physical qubits all with different chemical shifts. This idea may provide new insights into extending qubit systems in the sense that it effectively utilizes the magnetically equivalent nuclei.
Quantum simulation uses a well-known quantum system to predict the behavior of another quantum system. Certain limitations in this technique arise, however, when applied to specific problems, as we demonstrate with a theoretical and experimental study of an algorithm proposed by Wu, Byrd, and Lidar [Phys. Rev. Lett. 89, 057904 (2002).10.1103/PhysRevLett.89.057904] to find the low-lying spectrum of a pairing Hamiltonian. While the number of elementary quantum gates required scales polynomially with the size of the system, it increases inversely to the desired error bound E. Making such simulations robust to decoherence using fault tolerance requires an additional factor of approximately 1/E gates. These constraints, along with the effects of control errors, are illustrated using a three qubit NMR system.