Dynamical Decoupling of Qubits in Spin Bath under Periodic Quantum Control

TL;DR

This paper explores how to effectively preserve coherence and entanglement of spin qubits in a quantum spin chain using optimized dynamical decoupling sequences, considering practical pulse limitations and magnetic field effects.

Contribution

It introduces exact nontrivial pulse sequences that suppress qubit-bath coupling to high order with minimal pulses, enhancing coherence and entanglement preservation in realistic conditions.

Findings

Sequences with 4 or 7 pulses optimize performance under laboratory magnetic fields.

Alternating pulse directions between x and z improve coherence.

Pulse-width effects limit sequences to fewer than 10 pulses per cycle.

Abstract

We investigate the feasibility for the preservation of coherence and entanglement of one and two spin qubits coupled to an interacting quantum spin-1/2 chain within the dynamical decoupling (DD) scheme. The performance is examined by counting number of computing pulses that can be applied periodically with period of $T$ before qubits become decoherent, while identical decoupling pulse sequence is applied within each cycle. By considering pulses with mixed directions and finite width controlled by magnetic fields, it is shown that pulse-width accumulation degrades the performance of sequences with larger number of pulses and feasible magnetic fields in practice restrict the consideration to sequences with number of decoupling pulses being less than 10 within each cycle. Furthermore, within each cycle $T$, exact nontrivial pulse sequences are found for the first time to suppress the qubit-bath coupling to $O(T^{N+1})$ progressively with minimum number of pulses being $4,7,12$ for $N=1,2,3$. These sequences, when applied to all qubits, are shown to preserve both the entanglement and coherence. Based on time-dependent density matrix renormalization, our numerical results show that for modest magnetic fields (10-40 Tesla) available in laboratories, the overall performance is optimized when number of pulses in each cycle is 4 or 7 with pulse directions be alternating between x and z. Our results provide useful guides for the preservation of coherence and entanglement of spin qubits in solid state.