Abstract
Coherence of solid state spin qubits is limited by decoherence and random fluctuations in the spin bath environment. Here we develop spin bath control sequences which simultaneously suppress the fluctuations arising from intrabath interactions and inhomogeneity. Experiments on neutral self-assembled quantum dots yield up to a five-fold increase in coherence of a bare nuclear spin bath. Numerical simulations agree with experiments and reveal emergent thermodynamic behaviour where fluctuations are ultimately caused by irreversible conversion of coherence into many-body quantum entanglement. Simulations show that for homogeneous spin baths our sequences are efficient with non-ideal control pulses, while inhomogeneous bath coherence is inherently limited even under ideal-pulse control, especially for strongly correlated spin-9/2 baths. These results highlight the limitations of self-assembled quantum dots and advantages of strain-free dots, where our sequences can be used to control the fluctuations of a homogeneous nuclear spin bath and potentially improve electron spin qubit coherence.
Highlights
Coherence of solid state spin qubits is limited by decoherence and random fluctuations in the spin bath environment
In the case of homogeneous spin baths, we find that cyclic application of combined Hahn and solid echo (CHASE) sequences can efficiently suppress spin–spin entanglement, leading to significant extension of coherence times even under nonideal control pulses
We show that many-body decoherence emerges naturally under unitary evolution[30]: similar to the second law of thermodynamics, where useful energy is irreversibly dissipated into wasteful heat, the coherence is irreversibly converted into multipartite spin–spin entanglement
Summary
Coherence of solid state spin qubits is limited by decoherence and random fluctuations in the spin bath environment. In the case of homogeneous spin baths, we find that cyclic application of CHASE sequences can efficiently suppress spin–spin entanglement, leading to significant extension of coherence times even under nonideal control pulses.
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