We propose and analyze a new approach for quantum state transfer between remote spin qubits. Specifically, we demonstrate that coherent quantum coupling between remote qubits can be achieved via certain classes of random, unpolarized (infinite temperature) spin chains. Our method is robust to coupling strength disorder and does not require manipulation or control over individual spins. In principle, it can be used to attain perfect state transfer over arbitrarily long range via purely Hamiltonian evolution and may be particularly applicable in a solid-state quantum information processor. As an example, we demonstrate that it can be used to attain strong coherent coupling between Nitrogen-Vacancy centers separated by micrometer distances at room temperature. Realistic imperfections and decoherence effects are analyzed.PACS numbers: 03.67. Lx, 03.67.Hk, 05.50.+q, 75.10.Dg In addition to diverse applications ranging from quantum key distribution to quantum teleportation [1, 2], reliable quantum state transfer between distant qubits forms an essential ingredient of any scalable quantum information processor [3]. However, most direct qubit interactions are short-range and the corresponding interaction strength decays rapidly with physical separation. For this reason, most of the feasible approaches that have been proposed for quantum computation rely upon the use of quantum channels which serve to connect remote qubits; such channels include: electrons in semiconductors [4], optical photons [5][6][7][8], and the physical transport of trapped ions [9]. Coupled quantum spin chains have also been extensively studied [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24]. A key advantage of such spin chain quantum channels is the ability to manipulate, transfer, and process quantum information utilizing the same fundamental hardware [25]; indeed, both quantum memory and quantum state transfer can be achieved in coupled spin chain arrays [26], eliminating the requirement for an external interface between the quantum channel and the quantum register. Prior work on spin chain quantum channels has focused on three distinct regimes, in which the spin chain is either initialized [10][11][12][13]24], engineered [15,27,29] or dynamically controlled [19,28,[30][31][32]].An important application of spin-chain mediated coherent coupling is in the context of realizing a room temperature quantum information processor based upon localized spins in the solid-state [33]. In this case, it is difficult to envision mechanical qubit transport, while other coupling mechanisms are often not available or impose additional prohibitive requirements such as cryogenic cooling [8]. At the same time, long spin chains are generally difficult to polarize, impossible to control with single-spin resolution, and suffer from imperfect spin-positioning [21,22]; such imperfections can cause both on-site and coupling disorder, resulting in localization [34]. For these reasons, a detailed understanding of quantum coherence and state transfer in rando...
