发展固态量子信息与计算的实验研究

量子计算与量子信息是21世纪基础和应用科学研究的一大挑战. 要实现实用意义上的量子信息和量子计算,必须解决量子比特系统的可拓展性问题.基于现代半导体技术的固态量子系统,其应用和最终产业化的可行性较高. 然而,固态量子体系受周边环境的影响比较严重,控制其退相干,维持其量子状态的难度更高.实验固态量子计算的研究是个新的领域,尚无实用的技术和方法. 文章介绍了中国科学院物理研究所固态量子信息和计算实验室近几年来新开辟的自旋、 冷原子、 量子点(包括原子空位)、功能氧化物和关联体系等固态量子信息的新载体和同量子计算与量子信息相关的科学与技术难题的实验研究.     

中国科学院物理研究所固态量子信息与计算实验室

以场效应晶体管为代表的传统电子技术已经把人类社会带入了信息时代。但是,随着全球信息化的不断发展,传统信息技术在运算能力、存储量和安全性等多个方面固有的发展瓶颈正逐步显现出来。     

Enhanced quantum state detection efficiency through quantum information processing

We investigate theoretically and experimentally how quantum state-detection efficiency is improved by the use of quantum information processing (QIP). Experimentally, we encode the state of one 9Be(+) ion qubit with one additional ancilla qubit. By measuring both qubits, we reduce the state-detection error in the presence of noise. The deviation from the theoretically allowed reduction is due to infidelities of the QIP operations. Applying this general scheme to more ancilla qubits suggests that error in the individual qubit measurements need not be a limit to scalable quantum computation.     

Perfect quantum information processing with Dicke-class state

We investigate the possibility of implementing perfectquantum information processing with Dicke-class state. It is shownthat the symmetric Dicke state |D_N ^(m)〉 only has themaximal bipartite entanglement of one ebit when N = 2m andgenerally it is not maximally entangled for all bipartitions. Byadjusting the suitable weights and relative phases in the Dickestate |D_N ^(m)〉, we present a class of asymmetric Dickestates \(|\overline D_N^{(m)}\rangle\) which have the maximalbipartite entanglement of q (1 ≤ q ≤ m) ebits. We also obtainthe sufficient and necessary condition that the Dicke-class states\(|\overline D_{N}^{(m)}\rangle\) have the maximal bipartiteentanglement. We illustrate our idea using the four-qubit Dickestate with two excitations. It is shown that our proposedDicke-class states have distinct advantages over the symmetric Dickestate in perfect quantum information processing.     

Ion-trap quantum information processing: Experimental status

Atomic ions trapped in ultra-high vacuum form an especially well-understood and useful physical system for quantum information processing. They provide excellent shielding of quantum information from environmental noise, while strong, well-controlled laser interactions readily provide quantum logic gates. A number of basic quantum information protocols have been demonstrated with trapped ions. Much current work aims at the construction of large-scale ion-trap quantum computers using complex microfabricated trap arrays. Several groups are also actively pursuing quantum interfacing of trapped ions with photons.     

Photonic quantum information processing

Information processing with light is ubiquitous, from communication, metrology and imaging to computing. When we consider light as a quantum mechanical object, new ways of information processing become possible. In this review I give an overview of how quantum information processing can be implemented with single photons, and what hurdles still need to be overcome to implement the various applications in practice. I will place special emphasis on the quantum mechanical properties of light that make it different from classical light, and how these properties relate to quantum information processing tasks.     

核磁共振量子信息处理研究的新进展

过去的二十年中,量子信息相关研究取得了显著的进展,重要的理论和实验工作不断涌现.与其他量子信息处理系统相比,基于自旋动力学的核磁共振系统,不仅具有丰富而且成熟的控制技术,还拥有相干时间长、脉冲操控精确、保真度高等优点.这也是核磁共振体量子系统能够精确操控多达12比特的量子系统的原因.因此,核磁共振量子处理器在量子信息领域一直扮演着重要角色.本文介绍核磁共振量子计算的基本原理和一些新研究进展.研究的新进展主要包括量子噪声注入技术、量子机器学习在核磁共振平台上的实验演示、高能物理和拓扑序的量子模拟以及核磁共振量子云平台等.最后讨论了液态核磁共振的发展前景和发展瓶颈,并对未来发展方向提出展望.     

Experimental realization of maximum confidence quantum state discrimination for the extraction of quantum information

We present the first experimental demonstration of the maximum confidence measurement strategy for quantum state discrimination. Applying this strategy to an arbitrary set of states assigns to each input state a measurement outcome which, when realized, gives the highest possible confidence that the state was indeed present. The theoretically optimal measurement for discriminating between three equiprobable symmetric qubit states is implemented in a polarization-based free-space interferometer. The maximum confidence in the measurement result is 2/3. This is the first explicit demonstration that an improvement in the confidence over the optimal minimum error measurement is possible for linearly dependent states.     

Distributed quantum information processing via quantum dot spins

We propose a scheme to engineer a non-local two-qubit phase gate between two remote quantum-dot spins. Along with one-qubit local operations, one can in principal perform various types of distributed quantum information processing. The scheme employs a photon with linearly polarisation interacting one after the other with two remote quantum-dot spins in cavities. Due to the optical spin selection rule, the photon obtains a Faraday rotation after the interaction process. By measuring the polarisation of the final output photon, a non-local two-qubit phase gate between the two remote quantum-dot spins is constituted. Our scheme may has very important applications in the distributed quantum information processing.     

Cavity quantum networks for quantum information processing in decoherence-free subspace

We give a brief review on the quantum information processing in decoherence-free subspace (DFS). We show how to realize the initialization of the entangled quantum states, information transfer and teleportation of quantum states, two-qubit Grover search and how to construct the quantum network in DFS, within the cavity QED regime based on a cavity-assisted interaction by single-photon pulses.      

Demonstration of sufficient control for two rounds of quantum error correction in a solid state ensemble quantum information processor

We report the implementation of a 3-qubit quantum error-correction code on a quantum information processor realized by the magnetic resonance of carbon nuclei in a single crystal of malonic acid. The code corrects for phase errors induced on the qubits due to imperfect decoupling of the magnetic environment represented by nearby spins, as well as unwanted evolution under the internal Hamiltonian. We also experimentally demonstrate sufficiently high-fidelity control to implement two rounds of quantum error correction. This is a demonstration of state-of-the-art control in solid state nuclear magnetic resonance, a leading test bed for the implementation of quantum algorithms.