Quantum

Cavity-assisted dynamic nuclear polarisation

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Briefings

A new cavity-based dynamic nuclear polarisation (DNP) protocol was implemented using an ensemble of bismuth donor spins in isotopically purified silicon coupled to a superconducting resonator. A single cycle combining adiabatic microwave and radio-frequency pulses with Purcell relaxation increased the target ground state's population by a factor of 1.79±0.04, while additional cycles achieved a cumulative enhancement of 4.6±0.2. This result exceeds the theoretical limit of ninefold set by the degeneracy of the ground manifold. The observed enhancement is attributed to a competition between Purcell and intrinsic relaxation, alongside a collective effect that slows electronic spin radiative decay as nuclear spin population grows. Radiative DNP is now available as a mechanism at millikelvin temperatures where phonon-mediated relaxation is frozen.

Key points

• The study introduces a cavity-based DNP mechanism using Purcell relaxation to transfer polarisation from electron to nuclear spins in bismuth donor spins within isotopically purified silicon.

Context and limitations

Data represents a single experimental cycle and cumulative enhancement over multiple cycles; theoretical limits and specific failure modes remain untested.

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