In optomechanics, the mechanical oscillator usually outlives the photon in the cavity: its quality factor is higher. But if you swap the roles, the mechanical mode becomes a cold dissipative reservoir for light. Such a reversed regime has already been realized in superconducting circuits and is used for quantum amplification and entanglement. Related work in this area includes nonreciprocal transparency, ground-state cooling, and squeezed light generation in similar setups. This article places the parametric dynamical Casimir effect in that context: photon creation from the vacuum via laser frequency modulation, rather than via moving boundaries.
The authors take an experimentally realized microwave optomechanical circuit with two inductively coupled LC resonators. An auxiliary mode cools the mechanical oscillator to strong damping, after which the mechanical degree of freedom is adiabatically eliminated, leaving an effective Hamiltonian with Kerr nonlinearity. The laser frequency is then slowly modulated harmonically with amplitude on the order of 0.01–0.1. For analysis, they use numerical solution of the master equation in QuTiP and an analytical solution via the Wei–Norman theorem in the weak-coupling approximation. Key parameters: mechanical frequency 5.33 MHz, cavity damping 118 kHz, temperature below 10 mK.
Laser frequency modulation leads to the creation of microwave photons from the vacuum: the dynamical Casimir effect. The Kerr nonlinearity, arising from the elimination of the mechanics, saturates photon number growth and induces oscillations in time. For weak nonlinearity, the photon number grows exponentially; for strong nonlinearity, it oscillates. In a certain regime, photons exhibit sub-Poissonian statistics (Mandel parameter down to −0.5) and simultaneously Wigner negativity. Quadrature squeezing reaches 4.3 dB in the full model and 5 dB in the weak-coupling approximation. The photon generation rate varies from 10 MHz to 1.23 GHz depending on parameters.
The work shows that the reversed dissipative regime of optomechanics allows not only cooling and amplification but also the generation of nonclassical states of light. Unlike neighboring studies that limited themselves to squeezing or entanglement, here for the first time both sub-Poissonian statistics and Wigner negativity are obtained simultaneously in a single scheme. This is achieved via a tunable Kerr nonlinearity induced by the mechanical oscillator, rather than fixed by the material. Such a source of nonclassical microwave radiation could become a building block for quantum networks and sensors.
Further development could proceed along the path of integration with superconducting qubits: nonclassical microwave states are needed for quantum gates and error correction. Increasing the coupling g0 by reducing the capacitor gap or raising the resonator frequency would strengthen the nonlinearity. It is also interesting to explore multiphoton processes and the generation of entangled states between multiple resonators in the reversed regime.
The results could impact quantum computing, microwave quantum sensing, and quantum communication. In particular, nonclassical microwave photons are useful for quantum radar and quantum illumination.
Experimental realization of the proposed scheme in existing superconducting circuits with precise control of temperature and pump power. Then, measurement of the Wigner function and verification of simultaneous nonclassicality.
The work directly addresses the problem of generating nonclassical states of light in the microwave domain, where existing sources are limited to either squeezing or sub-Poissonian statistics, but not both at once. It also raises the question of the role of dissipation in quantum optics: the reversed regime turns loss into a resource.
This section is addressed to the author of the paper and their colleagues. Neighbouring works were found by meaning-based search across our archive, not by word overlap. We do not review: we show the field around the work.
What the work does
The authors study a superconducting optomechanical circuit in the reversed dissipative regime, where the mechanical oscillator decays faster than the microwave resonator. Slow modulation of the laser frequency induces the dynamical Casimir effect, creating photon pairs from the vacuum, while the induced Kerr nonlinearity saturates the growth and endows the photons with both sub-Poissonian statistics and Wigner negativity.
Where its strength is
For the first time, both sub-Poissonian statistics and Wigner negativity are obtained simultaneously in a single optomechanical setup, which is unattainable in standard schemes. The tunable Kerr nonlinearity, induced by the mechanical oscillator, opens a pathway to controlling nonclassical properties of radiation.
Where it could go next
Worth trying
Why this may matter
Such a source of nonclassical microwave radiation could serve as a building block for quantum networks, sensors, and computing, where states with both sub-Poissonian statistics and Wigner negativity are required.
Nearby works in our archive
The archive is sparse around this work: the closest review is only 0.55, against a usual 0.64. It looks like few have drilled nearby.
The mechanical oscillator in this scheme oscillates at 5.33 MHz, which is about 100 times lower than the FM radio band, yet it is cooled to below 10 mK, which is 30 times colder than the cosmic microwave background.
In the TV series 'The Expanse', the vacuum is not empty but teeming with virtual particles that can be extracted with advanced technology. The dynamical Casimir effect is a step in that direction: it turns quantum fluctuations into real photons.