Quantum state transfer between distant nodes is at the heart of quantum processing and quantum networking. Stimulated by this, we propose a scheme where one can achieve quantum state transfer with a high fidelity between sites in a cavity quantum optomechanical network. In our lattice, each individual site is composed of a localized mechanical mode which interacts with a laser-driven cavity mode via radiation pressure, while photons hop between neighboring sites. After diagonalization of the Hamiltonian of each cell, we show that the system can be reduced to an effective Hamiltonian of two decoupled bosonic chains, and therefore we can apply the well-known results in quantum state transfer together with an additional condition on the transfer times. In fact, we show that our transfer protocol works for any arbitrary joint quantum state of a mechanical and an optical mode. Finally, in order to analyze a more realistic scenario we take into account the effects of independent thermal reservoirs for each site. By solving the standard master equation within the Born-Markov approximation, we reassure both the effective model and the feasibility of our protocol.
Quantum state transfer between distant nodes is at the heart of quantum processing and quantum networking. Stimulated by this, we propose a scheme where one can achieve quantum state transfer with a high fidelity between sites in a cavity quantum optomechanical network. In our lattice, each individual site is composed of a localized mechanical mode which interacts with a laser-driven cavity mode via radiation pressure, while photons hop between neighboring sites. After diagonalization of the Hamiltonian of each cell, we show that the system can be reduced to an effective Hamiltonian of two decoupled bosonic chains, and therefore we can apply the well-known results in quantum state transfer together with an additional condition on the transfer times. In fact, we show that our transfer protocol works for any arbitrary joint quantum state of a mechanical and an optical mode. Finally, in order to analyze a more realistic scenario we take into account the effects of independent thermal reservoirs for each site. By solving the standard master equation within the Born-Markov approximation, we reassure both the effective model and the feasibility of our protocol.
We propose a scheme to implement quantum state transfer between two distant quantum nodes via a hybrid solid–optomechanical interface. The quantum state is encoded on the native superconducting qubit, and transferred to the microwave photon, then the optical photon successively, which afterwards is transmitted to the remote node by cavity leaking, and finally the quantum state is transferred to the remote superconducting qubit. The high efficiency of the state transfer is achieved by controllable Gaussian pulses sequence and numerically demonstrated with theoretically feasible parameters. Our scheme has the potential to implement unified quantum computing–communication–computing, and high fidelity of the microwave–optics–microwave transfer process of the quantum state.
We present a systematic study on the effects of dynamical transfer and steady-state synchronization of quantum states in a hybrid optomechanical network consisting of two cavities, which carry atoms inside and interact via a common moving mirror such as the mechanical oscillator. It is found that a high fidelity transfer of Schrödinger’s cat and squeezed states between two cavities modes is possible. On the other hand, we demonstrate the synchronization effect of the cavity modes in a steady squeezed state with its high fidelity realized by the mechanical oscillator that intermediates the generation, transfer and stabilization of the squeezing. In this framework, we also study the generation and evolution of bipartite and tripartite entanglement and find its connection to the effects of quantum state transfer and synchronization. Particularly, when the transfer occurs at the maximal fidelity, any entanglement is almost zero, so the different cavity modes are disentangled. However, these modes become entangled when the two bosonic modes are synchronized in a stationary squeezed state. The results provided by the current study may find applications in quantum information technologies, in addition to the setups for metrology, where squeezed states are essential.
In a hybrid scheme, consisting of a three-level atom-cavity-oscillator system, we show that synchronization [J. Czartowski, R. M\"uller, K. \ifmmode \dot{Z}\else \.{Z}\fi{}yczkowski, and D. Braun, Phys. Rev. A 104, 012410 (2021)] and transfer of nonclassical states between the mechanical oscillator and the cavity field is possible. In this framework, we show that an initially thermalized mechanical oscillator, when connected to a squeezed bath, evolves to a squeezed state which in steady state is synchronized with the cavity mode. On the other hand, if the mechanical oscillator is initially prepared in a nonclassical state, e.g., squeezed and Schr\"odinger's cat states, while the cavity is in a thermal state, then a periodic transfer between the mechanical oscillator and cavity mode occurs for given interaction times. As qualitative results, we prove that the synchronization and transfer of the quantum states are feasible with high fidelity.
State transfer between light and microwaves is a key challenge in quantum networks. Promising transducers use a mechanical intermediary that couples to both fields via radiation pressure. Such electro-optomechanical devices have achieved high efficiencies, yet require resolved-sideband cavities, and generally compromise in scalability and noise performance. Here, we relax this constraint by extending the protocol of Navarathna et al. that transfers optical quantum information onto a mechanical resonator using a broadband, sideband-unresolved cavity and feedback. Combining this with parametric mechanical-to-microwave conversion, we show that continuous optical-to-microwave quantum state transfer is possible using measurement-based feedback, while all-optical coherent feedback enables bidirectional transfer. To assess the transfer, we introduce the quantum transfer witness WT, which -- though similar to the input-referred added noise -- also identifies whether a channel is capable of both preserving Gaussian entanglement and outperforming classical transduction schemes. Finally, we show that quantum-compatible noise performance is within reach of current experimental capabilities. Our results unlock a new design space for electro-optomechanical transducers and strengthens their candidacy as scalable quantum links between distant nodes.
We describe a new scheme to interconvert stationary and photonic qubits which is based on indirect qubit-light interactions mediated by a mechanical resonator. This approach does not rely on the specific optical response of the qubit and thereby enables optical quantum interfaces for a wide range of solid state spin and charge based systems. We discuss the implementation of state transfer protocols between distant nodes of a quantum network and show that high transfer fidelities can be achieved under realistic experimental conditions.
A multipartite quantum system is entangled when its state cannot be factorized into a product of states or a mixture of such products. Quantum information schemes that exploit this purely quantum mechanical feature have been devised initially for systems with two discrete quantum levels (i.e., qubits), and afterward, extended to continuous-variable (CV) systems characterized by observables with continuous spectra, such as the position and momentum of a particle, or the quadratures of an electromagnetic field. Optomechanical systems, such as a driven optical cavity with vibrating end-mirrors or a classical coherent field scattering sidebands off a freely suspended mirror, hold a promise of being candidates for CV quantum information processing applications. As in most other proposals, light is the information carrier; the difference lies in the choice of a micromirror as a quantum storage device. Desired quantum states can be encoded in acoustic modes. The optomechanical coupling, owing to which quantum state transfer between radiation and mirror is possible, is realized via the radiation pressure effect, which consists in momentum transfer between field and mirror during the scattering process. The use of the vibrational modes of a micromirror as a quantum state encoder system is somehow unexpected because this is a macroscopic ensemble of atoms expected to behave rather classically. However, there are proposals that show that, in principle, the vibrational occupation number of even such a large collection of atoms in a solid can be reduced close to zero, which signifies a clear transition from the classical to the quantum regime. Remarkable progress has been made to experimentally cool the resonator by a few orders of magnitude to quite low occupation numbers. However, in order to approach the quantum limit, one needs to integrate small, light, and flexible micromechanical elements into high-finesse cavities (which are typically much more rigid and massive), which is technically challenging. Furthermore, the mechanical quality factor has to be quite high, but present microfabrication techniques yield a mechanical quality factor scaling down for smaller and smaller microresonators. This chapter starts with developing a general framework for treating the dynamics of a driven optical cavity with a vibrating end-mirror system in which two cooling techniques have been recently demonstrated: (i) cold-damping quantum feedback, where the oscillator position is measured through a phase-sensitive detection of the cavity output and the resulting photocurrent is used for a real-time correction of the dynamics, and (ii) backaction or self-cooling, in which the off-resonant operation of the cavity results in a retarded back action on the mechanical system, and hence, in a “self”-modification of its dynamics. The two situations are illustrated in Fig. 24.1. Analytical results for the final phonon number are obtained for both schemes and their applicability within today's state-of-the-art laboratory setups is analyzed.