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Physical Review Research

Deterministic generation of large Fock states in coupled optical-optomechanical cavities

Xinchen Zhang, Nuo Wang, Zhaohua Tian, Qi Liu, Ying Gu

Published Jul 24, 2025• 1 citation
Publisher

Abstract

The preparation of Fock states, as a fundamental problem in the research of quantum optics and quantum information, still faces challenges in achieving both unconditional preparation and large photon numbers. Here, we study the deterministic generation of large Fock states through the nonlinear interaction in coupled optical-optomechanical cavities. Under the condition that the mechanical frequency is twice the optical coupling strength, and much larger than the optomechanical coupling strength, there occurs a nonlinear interaction among two optical eigenmodes and the mechanical mode, i.e., a photon is annihilated, accompanied by the creation of another photon together with a phonon, and vice versa. It is analytically proved that, through this interaction, Fock states | n 〉 and | 1 〉 will generate | n + 1 〉 at specific evolution times if the mechanical mode is initially on the ground state. In addition, numerical results show that Fock states | n 〉 and | p 〉 can also generate | n + p 〉 with the fidelities larger than 94% ( 1 < p ≤ n ≤ 40 ). The proposed mechanism achieves deterministic generation of large Fock states, which can be applied to quantum metrology and quantum simulation.

DOI
10.1103/j7yp-fg9g

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The preparation of Fock states, as a fundamental problem in the research of quantum optics and quantum information, still faces challenges in achieving both unconditional preparation and large photon numbers. Here, we study the deterministic generation of large Fock states through the nonlinear interaction in coupled optical-optomechanical cavities. Under the condition that the mechanical frequency is twice the optical coupling strength, and much larger than the optomechanical coupling strength, there occurs a nonlinear interaction among two optical eigenmodes and the mechanical mode, i.e., a photon is annihilated, accompanied by the creation of another photon together with a phonon, and vice versa. It is analytically proved that, through this interaction, Fock states | n 〉 and | 1 〉 will generate | n + 1 〉 at specific evolution times if the mechanical mode is initially on the ground state. In addition, numerical results show that Fock states | n 〉 and | p 〉 can also generate | n + p 〉 with the fidelities larger than 94% ( 1 < p ≤ n ≤ 40 ). The proposed mechanism achieves deterministic generation of large Fock states, which can be applied to quantum metrology and quantum simulation.
The quantization of the electromagnetic field leads directly to the existence of quantum mechanical states, called Fock states, with an exact integer number of photons. Despite these fundamental states being long-understood, and despite their many potential applications, generating them is largely an open problem. For example, at optical frequencies, it is challenging to deterministically generate Fock states of order two and beyond. Here, we predict the existence of an effect in nonlinear optics, which enables the deterministic generation of large Fock states at arbitrary frequencies. The effect, which we call an n -photon bound state in the continuum, is one in which a photonic resonance (such as a cavity mode) becomes lossless when a precise number of photons n is inside the resonance. Based on analytical theory and numerical simulations, we show that these bound states enable a remarkable phenomenon in which a coherent state of light, when injected into a system supporting this bound state, can spontaneously evolve into a Fock state of a controllable photon number. This effect is also directly applicable for creating (highly) squeezed states of light, whose photon number fluctuations are (far) below the value expected from classical physics (i.e., shot noise). We suggest several examples of systems to experimentally realize the effects predicted here in nonlinear nanophotonic systems, showing examples of generating both optical Fock states with large n ( n > 10), as well as more macroscopic photonic states with very large squeezing, with over 90% less noise (10 dB) than the classical value associated with shot noise.
We put forward a deterministic dissipative protocol to prepare phonon Fock states in nonlinear quantum optomechanical devices. The system is composed of a mechanical mode interacting with an optical field via radiation pressure, whereas the light mode is laser driven in the resolved blue-sideband regime. To keep our results tractable, we switch to an interaction picture in a displaced basis, where the effective Hamiltonian exhibits the selective photon-phonon interaction explicitly. After proper parameter adjustment and similarly to cavity-cooling schemes, the quantum evolution allows steering of the mechanical degree of freedom to the desired Fock state by directing the optical excitations dynamically towards the target phonon state. The numerical results, including decoherence on both the mechanical and the optical degrees of freedom, prove to be quite robust in the good- and bad-cavity regimes, with fidelities exceeding 95%. Finally, characterization of the achieved nonclassicality, as well as the limitations and feasibility of our protocol under experimental parameters, is also discussed.
In this paper, we propose a scheme for deterministically preparing a quantum superposition $|{\ensuremath{\psi}}_{s}{\ensuremath{\rangle}}_{b}={C}_{0}{|0\ensuremath{\rangle}}_{b}+{C}_{\mathcal{N}}{|\mathcal{N}\ensuremath{\rangle}}_{b}$ between vacuum and an arbitrary Fock state ${|\mathcal{N}\ensuremath{\rangle}}_{b}$ of mechanical oscillators via strong single-photon optomechanical coupling. We consider an optomechanical cavity which contains a Kerr medium and is driven by two lasers, with one laser tuned to the cavity resonance and the other to the N\mathcal{N}Nth lower sideband of the cavity. The amplitudes C0{C}_{0}C0​ and CN{C}_{\mathcal{N}}CN​ are determined only by the drive strengths in the absence of mechanical damping and the approximate Fock state $|{\ensuremath{\psi}}_{s}{\ensuremath{\rangle}}_{b}\ensuremath{\approx}{|\mathcal{N}\ensuremath{\rangle}}_{b}$ can be obtained with appropriate relative strengths of the lasers. It is revealed that the superposition results from destructive quantum interference. The analytical results are confirmed by exact numerical calculation, and it is also shown that the nonclassical state is robust against thermal mechanical noise.
Using quadratic optomechanical coupling to prepare high-purity mechanical cat states is not feasible as its strength is several orders weaker than linear optomechanical coupling. Here, using only linear coupling in a multimode system, we achieve strong interaction between photons and two phonons, enabling the deterministic generation of high-purity multicomponent mechanical cats. Mediated by an auxiliary supermode, when other two optical supermodes satisfy the two-phonon resonance condition, the process whereby the annihilation of a high-frequency photon accompanied by the creation of a low-frequency photon and two phonons is strongly enhanced. Such resonant two-phonon process drives multiple rotations and interferences of mechanical coherent states, deterministically generating a multicomponent mechanical cat immune to both mechanical and optical losses. Our work provides an universal strategy for enhancing high-order phonon nonlinearities, paving the way for quantum state engineering, quantum precision measurement and fault-tolerant quantum computation.
We propose a protocol for the deterministic preparation of entangled NOON mechanical states. The system is constituted by two identical, optically coupled optomechanical systems. The protocol consists of two steps. In the first, one of the two optical resonators is excited by a resonant external $\ensuremath{\pi}$-like Gaussian optical pulse. When the optical excitation coherently partly transfers to the second cavity, the second step starts. It consists of sending simultaneously two additional $\ensuremath{\pi}$-like Gaussian optical pulses, one at each optical resonator, with specific frequencies. In the optomechanical ultrastrong coupling regime, when the coupling strength becomes a significant fraction of the mechanical frequency, we show that NOON mechanical states with quite high Fock states can be deterministically obtained. The operating range of this protocol is carefully analyzed. Calculations have been carried out taking into account the presence of decoherence, thermal noise, and imperfect cooling.
An optical field with a definite number of photons is very important for quantum metrology and quantum information. Some theoretical protocols for creating such a Fock-state have been proposed, but it is still a big challenge to produce it with a large number photons experimentally. We revisit the system of atoms inside an optical parametric oscillator that was proposed in 1990s, and it is found that for the atom ensemble, the optical Fock-state with an arbitrary number of photons can be generated. Compared to the previous proposals, the scheme presented here is simple and seems physically realizable. The system also provides the possibility to demonstrate the strong interaction between nonclassical light and atoms in a confined space.