Initialization and readout of spin chains for quantum information transport

Abstract

Abstract. Linear chains of spins acting as quantum wires are a promising approach for achieving scalable quantum information processors. Nuclear spins in apatite crystals provide an ideal test bed for the experimental study of quantum information transport, as they closely emulate a one-dimensional spin chain, while magnetic resonance techniques can be used to drive the spin chain dynamics and probe the accompanying transport mechanisms. Here we demonstrate initialization and readout capabilities in these spin chains, even in the absence of single-spin addressability. These control schemes enable preparing desired states for quantum information transport and probing their evolution under the transport Hamiltonian. We further optimize the control schemes by a detailed analysis of 19 F NMR lineshape.

Implementation of State Transfer Hamiltonians in Spin Chains with Magnetic Resonance Techniques

“…Multiple quantum coherence techniques were later used to further characterize the system [138]; conversely, the system was used to gain a better insight into the dynamics of MQC [120,130,139] and discrepancies with theoretical models adopted for MQC growth in 3D systems lead to further theoretical analysis [142,143]. More recently, FAp crystals have been proposed as a quantum information processing platform [18,144] and used to study quantum information transport [12,101,118,119,134] in a quasi-1D nuclear spin system, as we will present in the following.…”

“…In a distributed architecture, the qubit might be a different physical system that is put in contact with the spin wire when transport is required. In NMR-based experimental efforts to demonstrate QST, the qubit is often the spin at the end of the chain [12,134]. Thus we would like to initialize it in a state of interest for the transfer of either classical or quantum information, while leaving the rest of the spin chain in the maximally mixed state.…”

“…Unfortunately, collective control of all the pulses in the chains, as given by on-resonance RF pulses, seems to preclude the preparation of these states. However exploiting the spin natural dynamics and a combination of coherent and incoherent control it is possible not only to prepare [12], but even to detect these types of states [134]. This was one critical step toward the demonstration of QST in a solid-state NMR platform.…”

“…Under this approximation, the DQ Hamiltonian is exactly solvable by invoking a Jordan-Wigner mapping onto a system of free fermions [149,162]. The analytical solution for the evolution of the thermal state, when measuring the collective magnetization, is given by [119,134]:…”

“…(11) shows a complementary measurement where we start from thermal initial state, given by the collective magnetization, and read out the ends of the chains after evolution under the DQ Hamiltonian, S re ∝ Tr U MQ δ ρ th U † MQ δ ρ end . Both these data sets were fitted by the analytical expression [134]. Blue: Initial state δ ρ th ; readout, collective magnetization, Σ z .…”