Squeezed Phonon States Enhance Anharmonicity and Qubit Control in Mechanical Oscillators

Mechanical qubits represent a promising avenue in the pursuit of robust quantum technologies, offering extended coherence times and diverse application possibilities, yet they typically suffer from weak responsiveness to external stimuli. Yi-Fan Qiao from Xi’an Jiaotong University, Jun-Hong An from Lanzhou University, and Peng-Bo Li, also from Xi’an Jiaotong University, and their colleagues demonstrate a novel approach to overcome this limitation by harnessing squeezed states of phonons within a vibrating nanomechanical resonator. Their research introduces the ‘mechanical squeezed-Fock qubit’, a system where carefully engineered quantum states dramatically enhance the resonator’s sensitivity and allow for precise control of its quantum properties. This innovation unlocks significantly improved anharmonicity, suppressing unwanted transitions and boosting the qubit’s performance, and importantly, promises a sensitivity increase of at least one order of magnitude for detecting incredibly weak forces, paving the way for advanced quantum sensing and information processing.

Mechanical Resonators for Quantum Sensing and Computation

Mechanical resonators in the quantum realm represent a pivotal platform for advancing quantum science and technologies, offering promising pathways toward scalable quantum computation and ultra-precise sensing. Compared to their electromagnetic counterparts, mechanical resonators offer longer lifetimes, greater compactness, and the capability for direct coupling to different degrees of freedom, enabling quantum squeezing of mechanical motion, quantum transduction, and quantum entanglement. These resonators, particularly those exhibiting nonlinearities, are intriguing candidates for realizing mechanical qubits in quantum computation and, due to their ability to couple to external forces, offer potential for quantum force sensing with improved sensitivity. Traditionally, a mechanical qubit is encoded in the first two energy levels of a Kerr-nonlinear oscillator, requiring a large energy difference between transitions to minimize excitation of higher energy levels.

However, developing practical mechanical qubits has been limited by the inherent physical constraints of these systems, where nonlinearities are often weak. This research addresses this limitation by demonstrating a method to exponentially enhance these weak nonlinearities. This work demonstrates that weak intrinsic nonlinearities can be exponentially enhanced via two-phonon driving, enabling robust encoding of a mechanical qubit in the two lowest squeezed Fock states. This allows weakly nonlinear mechanical resonators to function as high-fidelity qubits rather than simple resonators.

Nanomechanical Resonators and Quantum Optomechanics

This research details a method to significantly enhance the performance of nanomechanical resonators for quantum sensing and computation. By employing two-phonon driving, we demonstrate the ability to exponentially amplify weak nonlinearities within these resonators, enabling robust encoding of a mechanical qubit in the two lowest squeezed Fock states. This approach allows for the creation of high-fidelity qubits from resonators that would otherwise exhibit limited quantum behavior. The enhanced nonlinearity allows for precise control and manipulation of the qubit, enabling its use in sensitive force measurements.

Simulations and analysis demonstrate that this method suppresses energy leakage and parasitic oscillations, leading to improved resolution and accuracy in detecting external signals. The sensitivity of the qubit increases with longer measurement times, but also becomes more susceptible to decoherence, highlighting the need for careful optimization of measurement parameters. This work represents a significant advancement in the field of quantum optomechanics, paving the way for the development of more sensitive and robust quantum sensors and potentially enabling new applications in areas such as gravitational wave detection and precision metrology. The ability to create high-fidelity qubits from weakly nonlinear resonators opens up new possibilities for quantum information processing and computation. This research builds upon a substantial body of work in nanomechanical resonators, quantum optomechanics, and related fields, reflecting the interdisciplinary nature of this research area and the growing importance of quantum effects, nonlinear dynamics, and materials innovation.