Month: June 2014

Optimized dynamical control of state transfer through noisy spin chains | New Journal of Physics

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Optimized dynamical control of state transfer through noisy spin chains

Analia Zwick, Gonzalo A Álvarez, Guy Bensky and Gershon Kurizki
Focus on Coherent Control of Complex Quantum Systems:
New J. Phys. 16, 065021 (2014).

We propose a method of optimally controlling the tradeoff of speed and fidelity of state transfer through a noisy quantum channel spin-chain. This process is treated as qubit state-transfer through a fermionic bath. We show that dynamical modulation of the boundary-qubits levels can ensure state transfer with the best tradeoff of speed and fidelity. This is achievable by dynamically optimizing the transmission spectrum of the channel. The resulting optimal control is robust against both static and fluctuating noise in the channelʼs spin–spin couplings. It may also facilitate transfer in the presence of diagonal disorder on site energy noise in the channel.

via Optimized dynamical control of state transfer through noisy spin chains – Abstract – New Journal of Physics – IOPscience.

Top inset: Spin-channel for state transfer with boundary-controlled couplings. Boundary-controlled spin chain mapped to a non-interacting spinless fermions system. The two boundary spins 0 and N+1 are resonantly coupled to the chain by the fermionic-mode z with a coupling strength J_z*α(t). (a) Spectrum of the effective fermionic system (rectangular bars) which interacts with the bath-modes k (red-even k and blue-odd k vertical lines) with strengths J ̃_k* α(t). Dashed contour: noise spectrum described by the Wigner-semicircle (maximal-disorder) lineshape with a central gap around ω_z. In the central gap, the optimal spectral-filters F_T(ω) generated by dynamical boundary-control with α_p(t) (p = 0 (black dotted), p = 2 (orange thin)) are shown. Bottom inset: a zoom of the tails of the filter spectrum that protect the state transfer against a general noisy bath with a central gap. (b) Infidelity as a function of transfer time T under optimal control (filter) with p = 0 (black dotted) and p = 2 (orange thin).
Top inset: Spin-channel for state transfer with boundary-controlled couplings. Boundary-controlled spin chain mapped to a non-interacting spinless fermions system. The two boundary spins 0 and N+1 are resonantly coupled to the chain by the fermionic-mode z with a coupling strength J_z*α(t). (a) Spectrum of the effective fermionic system (rectangular bars) which interacts with the bath-modes k (red-even k and blue-odd k vertical lines) with strengths J ̃_k* α(t). Dashed contour: noise spectrum described by the Wigner-semicircle (maximal-disorder) lineshape with a central gap around ω_z. In the central gap, the optimal spectral-filters F_T(ω) generated by dynamical boundary-control with α_p(t) (p = 0 (black dotted), p = 2 (orange thin)) are shown. Bottom inset: a zoom of the tails of the filter spectrum that protect the state transfer against a general noisy bath with a central gap. (b) Infidelity as a function of transfer time T under optimal control (filter) with p = 0 (black dotted) and p = 2 (orange thin).
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