Zhao-Ming Wang

Nonperturbative leakage elimination operators and control of a three-level system.

Dynamical decoupling operations have been shown to reduce errors in quantum information processing. Leakage from an encoded subspace to the rest of the system space is a particularly serious problem for which leakage elimination operators (LEOs) were introduced. Here we provide an analysis of nonideal pulses, rather than the well-understood idealization or bang-bang controls. Under realistic conditions, we show that these controls will provide the same protection from errors as idealized controls. Our work indicates that the effectiveness of LEOs depends on the integral of the pulse sequence in the time domain, which has been missing because of the idealization of pulse sequences. Our results are applied to a three-level system for the nitrogen-vacancy centers under an external magnetic field and are illustrated by the fidelity dynamics of LEO sequences, ranging from regular rectangular pulses, random pulses, and even disordered (noisy) pulses.

One Component Dynamical Equation and Noise Induced Adiabaticity

Department of Physics, Ocean University of China, Qingdao 266100, China(Dated: July 22, 2013)The adiabatic theorem addresses the dynamics of a target instantaneous eigenstate of a time-dependent Hamiltonian. We use a Feshbach P-Q partitioning technique to derive a closed one-component integro-differential equation. The resultant equation properly traces the footprint of thetarget eigenstate. The physical significance of the derived dynamical equation is illustrated by bothgeneral analysis and concrete examples. Surprisingly, we find an anomalous phenomenon showingthat a dephasing white noise can enhance and even induce adiabaticity. This new phenomenon maynaturally occur in many physical systems. We also show that white noises can also shorten the totalduration of dynamic processes such as adiabatic quantum computing.

High-fidelity state transfer over an unmodulated linear XY spin chain

We provide a class of initial encodings that can be sent with a high fidelity over an unmodulated, linear,

Nonperturbative dynamical decoupling control: A spin-chain model

mathit{XY}

Robust and reliable transfer of a qubit state through an XY spin chain

spin chain. As an example, an average fidelity of

Fault-tolerant breathing pattern in optical lattices as a dynamical quantum memory

96%

Identifying quantum states capable of high-fidelity transmission over a spin chain

can be obtained using an 11-spin encoding to transmit a state over a chain containing 10 000 spins. An analysis of the magnetic-field dependence is given, and conditions for field optimization are provided.

Quantum state transfer through a spin chain in a multiexcitation subspace

This paper considers a spin chain model by numerically solving the exact model to explore the non-perturbative dynamical decoupling regime, where an important issue arises recently (J. Jing, L.-A. Wu, J. Q. You and T. Yu, arXiv:1202.5056.). Our study has revealed a few universal features of non-perturbative dynamical control irrespective of the types of environments and system-environment couplings. We have shown that, for the spin chain model, there is a threshold and a large pulse parameter region where the effective dynamical control can be implemented, in contrast to the perturbative decoupling schemes where the permissible parameters are represented by a point or converge to a very small subset in the large parameter region admitted by our non-perturbative approach. An important implication of the non-perturbative approach is its flexibility in implementing the dynamical control scheme in a experimental setup. Our findings have exhibited several interesting features of the non-perturbative regimes such as the chain-size independence, pulse strength upper-bound, noncontinuous valid parameter regions, etc. Furthermore, we find that our non-perturbative scheme is robust against randomness in model fabrication and time-dependent random noise.

Shortcut to nonadiabatic quantum state transmission

We present several protocols for reliable quantum state transfer through a spin chain. We use a simple two-spin encoding to achieve a remarkably high fidelity transfer for an arbitrary quantum state. The fidelity of the transfer also decreases very slowly with increasing chain length. We find that we can also increase the reliability by taking advantage of a local memory and/or confirm transfer using a second spin-chain.

Adiabatic leakage elimination operator in an experimental framework

Proposals for quantum information processing often require the development of new quantum tech- nologies. However, here we build quantum memory by ultracold atoms in one-dimensional optical lattices with existing state-of-the-art technology. Under a parabolic external field, we demonstrate that an arbitrary initial state at an end of the optical lattices can time-evolve and revive, with very high fidelity, at predictable discrete time intervals. Physically, the parabolic field, can catalyze a breathing pattern. The initial state is memorized by the pattern and can be retrieved at any of the revival time moments. In comparison with usual time-independent memory, we call this a dynamical memory. Furthermore, we show that the high fidelity of the quantum state at revival time moments is fault-tolerant against the fabrication defects and even time-dependent noise.