Quantum Control of Hybrid Spin-Oscillator Systems

Sebastian Saner

Jingfu Zhang, Swathi S. Hegde, Dieter Suter

We propose and demonstrate a quantum control scheme for hybrid quantum registers that can reduce the operation time, and therefore the effects of relaxation, compared to existing implementations. It combines resonant excitation pulses with periods of free precession under the internal Hamiltonian of the qubit system. We use this scheme to implement quantum gates like controlled-NOT operations on electronic and nuclear spins of the nitrogen-vacancy center in diamond. As a specific application, we transfer population between electronic and nuclear spin qubits and use it to measure the Rabi oscillations of a nuclear spin in a system with multiple coupled spins.

Raúl Coto, Hugo Molinares, Vitalie Eremeev

Quantum information transfer between light-matter-type systems is poised to enable important applications, while also serving as a testbed for theoretical investigation. Such systems can be realized with spins coupled to a mechanical oscillator, a platform that has been extensively studied both theoretically and experimentally. Early demonstrations of quantum information transfer have relied mostly on coherent control. However, measurement-induced backaction has emerged as a strong alternative for quantum control. In this work we use post-selection on the spin system as a selective backaction to refocus spin's phase information onto the mechanical oscillator. We identify physical resources and operating regimes that govern conditional phase transfer, including oscillator quantum coherence, the number of spins, the mechanical initial state, coupling strength, oscillator amplitude, and relaxation. We benchmark different scenarios using the variance as the figure of merit, estimated via two complementary approaches: a semiclassical variance estimator and a Pegg-Barnett quantum estimator. The Cramér-Rao bound is also computed for comparison. The analysis provides a framework for understanding phase transfer in high-dimensional hybrid quantum systems and for measurement-induced backaction used in quantum magnetometry.

Konrad W. Lehnert

Sungjoo Cho, Ju-yeon Gyhm, Hyukjoon Kwon +1 more

We propose a novel measurement-free scheme for stabilizing a spin-oscillator hybrid qubit via autonomous quantum error correction. The engineered Lindbladian renders the code space into an attractive steady-state subspace, realized by coupling the storage mode to a rapidly cooled bath through a controlled beam-splitter and spin-dependent displacement interactions. The continuous variable-discrete variable hybrid approach to autonomous quantum error correction preserves the hardware efficiency of conventional dissipation engineering while simplifying the required system-bath coupling. The construction is compatible with simple logical gates and leverages primitives already demonstrated in experimental platforms, such as trapped-ion systems, suggesting a practical route to hardware-efficient, noise-biased logical qubits without repeated syndrome measurements and feedforward.

Kai Shinbrough, Donovan J. Webb, Iver R. Øvergaard +4 more

Generalized squeezing interactions are foundational to quantum optics, and have recently come under experimental control in hybrid spin-oscillator quantum processors [O. Băzăvan, et al., Nat. Phys. 22, 757 (2026); S. Saner, et al., Phys. Rev. X 16, 021049 (2026)]. These interactions open the door for new applications in the processing of discrete- and continuous-variable quantum information, four of which we propose and investigate in this work: geometric phase gates mediated by spin-dependent generalized squeezing acting on two spins and a common oscillator; genuine N-body spin interactions mediated by individually addressed spin-dependent generalized squeezing; oscillator thermometry via spin readout; and the preparation of high-fidelity quantum states of the oscillator via spin-dependent generalized squeezing and mid-circuit measurement. A unifying feature of these applications is the geometric phase induced by generalized squeezing interactions, which is nonlinear in the Fock occupation of the oscillator and the interaction order of the generalized squeezing. This work provides a foundation for fast, high-fidelity discrete- and continuous-variable quantum computation and sensing in the hybrid spin-oscillator platform via generalized squeezing.