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Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)

Coherent quantum transport in waveguide lattices

Robert Keil, Armando Pérez-Leija, Alastair Kay, H. M. Moya-Cessa, Stefan Nolte, L. C. Kwek, B. M. Rodríguez-Lara, Alexander Szameit, Demetrios N. Christodoulides

Published May 1, 2013• 0 citations
Publisher

Abstract

The coherent transport of quantum states between distant qubits is one of the key milestones towards the realisation of large-scale quantum computers [1]. For static qubits, this state transfer is often envisioned to be carried out only by the internal dynamics of the system, which has the great advantage that detrimental influences of the environment are minimised. A chain of spin-1/2-qubits with ferromagnetic coupling has been suggested as an implementation of a coherent transport which is perfect in theory [2]. In this scheme, a precise engineering of the coupling strengths between adjacent spins is crucial. To date, such a quantum state transfer has only been achieved for the modest system size of three qubits, employing nuclear magnetic resonance [3]. However, this concept is by no means restricted to spin chains; it is therefore possible to resort to another physical platform, such as optics, to investigate the capabilities of the transferring Hamiltonian.

DOI
10.1109/cleoe-iqec.2013.6801687

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Jacob M. Taylor, Wolfgang D ur, G. Giedke +4 more

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The coherent transport of quantum states between distant qubits is one of the key milestones towards the realisation of large-scale quantum computers [1]. For static qubits, this state transfer is often envisioned to be carried out only by the internal dynamics of the system, which has the great advantage that detrimental influences of the environment are minimised. A chain of spin-1/2-qubits with ferromagnetic coupling has been suggested as an implementation of a coherent transport which is perfect in theory [2]. In this scheme, a precise engineering of the coupling strengths between adjacent spins is crucial. To date, such a quantum state transfer has only been achieved for the modest system size of three qubits, employing nuclear magnetic resonance [3]. However, this concept is by no means restricted to spin chains; it is therefore possible to resort to another physical platform, such as optics, to investigate the capabilities of the transferring Hamiltonian.
Spin chains have been proposed as quantum wires in many quantum-information processing architectures. Coherent transmission of quantum information in spin chains over short distances is enabled by their internal dynamics, which drives the transport of single-spin excitations in perfectly polarized chains. Given the practical challenge of preparing the chain in a pure state, we propose to use a chain that is initially in the maximally mixed state. We compare the transport properties of pure and mixed-state chains and find similarities that enable the experimental study of pure-state transfer via mixed-state chains. We also demonstrate protocols for the perfect transfer of quantum information in these chains. Remarkably, mixed-state chains allow the use of Hamiltonians that do not preserve the total number of single-spin excitations and are more readily obtainable from the naturally occurring magnetic dipolar interaction. We discuss experimental implementations using solid-state nuclear magnetic resonance and defect centers in diamond.
We present an introductory overview of the use of spin chains as quantum wires, which has recently developed into a topic of lively interest. The principal motivation is in connecting quantum registers without resorting to optics. A spin chain is a permanently coupled 1D system of spins. When one places a quantum state on one end of it, the state will be dynamically transmitted to the other end with some efficiency if the spins are coupled by an exchange interaction. No external modulations or measurements on the body of the chain, except perhaps at the very ends, is required for this purpose. For the simplest (uniformly coupled) chain and the simplest encoding (single qubit encoding), however, dispersion reduces the quality of transfer. We present a variety of alternatives proposed by various groups to achieve perfect quantum state transfer through spin chains. We conclude with a brief discussion of the various directions in which the topic is developing.
We present an introductory overview of the use of spin chains as quantum wires, which has recently developed into a topic of lively interest. The principal motivation is in connecting quantum registers without resorting to optics. A spin chain is a permanently coupled 1D system of spins. When one places a quantum state on one end of it, the state will be dynamically transmitted to the other end with some efficiency if the spins are coupled by an exchange interaction. No external modulations or measurements on the body of the chain, except perhaps at the very ends, is required for this purpose. For the simplest ( uniformly coupled) chain and the simplest encoding (single qubit encoding), however, dispersion reduces the quality of transfer. We present a variety of alternatives proposed by various groups to achieve perfect quantum state transfer through spin chains. We conclude with a brief discussion of the various directions in which the topic is developing.
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Spin chains have been proposed as wires to transport information between distributed registers in a quantum information processor. Unfortunately, the challenges in manufacturing linear chains with engineered couplings has hindered experimental implementations. Here we present strategies to achieve perfect quantum information transport in arbitrary spin networks. Our proposal is based on the weak coupling limit for pure state transport, where information is transferred between two end spins that are only weakly coupled to the rest of the network. This regime allows ignoring the complex, internal dynamics of the bulk network and relying on virtual transitions or on the coupling to a single bulk eigenmode. We further introduce control methods capable of tuning the transport process and achieve perfect fidelity with limited resources, involving only manipulation of the end qubits. These strategies could be thus applied not only to engineered systems with relaxed fabrication precision, but also to naturally occurring networks; specifically, we discuss the practical implementation of quantum state transfer between two separated nitrogen vacancy (NV) centers through a network of nitrogen substitutional impurities.