Entanglement of propagating optical modes via a mechanical interface

Abstract

Many applications of quantum information processing (QIP) require distribution of quantum states in networks, both within and between distant nodes [1]. Optical quantum states are uniquely suited for this purpose, as they propagate with ultralow attenuation and are resilient to ubiquitous thermal noise. Mechanical systems are then envisioned as versatile interfaces between photons and a variety of solid-state QIP platforms [2, 3]. Here, we demonstrate a key step towards this vision, and generate entanglement between two propagating optical modes, by coupling them to the same, cryogenic mechanical system. The entanglement persists at room temperature, where we verify the inseparability of the bipartite state and fully characterize its logarithmic negativity by homodyne tomography. We detect, without any corrections, correlations corresponding to a logarithmic negativity of E N = 0.35. Combined with quantum interfaces between mechanical systems and solid-state qubit processors already available [4, 5, 6, 7] or under development [8,9], this paves the way for mechanical systems enabling long-distance quantum information networking over optical fiber networks.Entanglement is a crucial resource for QIP [10]. As such, the ability to entangle fields of arbitrary wavelength will be important for linking nodes in heterogeneous QIP networks. Mechanical oscillators are uniquely poised in their ability to create such links, thanks to the frequency-independence of the radiation pressure interaction. The ability to entangle two radiation fields via a common mechanical interaction was outlined 20 years ago [11,12], and the intervening decades have seen the development of optomechanical devices [13] which are robustly quantum mechanical and routinely integrated into hybrid systems.Recently, mechanically-mediated entanglement has been reported between propagating microwave fields [14] as well as two superconducting qubits [15]. In both cases, the entanglement remained confined to the dilution refrigerator in which it was created. Here, we utilize an extremely coherent mechanical platform 1 arXiv:1911.05729v2 [quant-ph]

Optomechanical entanglement at room temperature: A simulation study with realistic conditions

“…Moreover, this entanglement persists at room temperature with realistic losses, stable optical spring detunings, and accessible circulating powers. With experimentally stable parameters, we predict a maximum logarithmic negativity versus temperature of E N = 0.2 in this parameter space; considering parameters close to reported optomechanical entanglement experiments yields an average logarithmic negativity of E N = 0.3 (with about 1% measurement certainty) which agrees with the results reported there [23]. Furthermore, we found that entanglement is highly temperature dependent, yet lowering losses is more effective.…”

“…Moreover, for input involving two light sources, an optomechanical cavity can output entangled light [18][19][20][21][22]. This form of bipartite optical entanglement generation has been demonstrated experimentally using a vibrating silicon oxide membrane [23]. This work considers a cantilever micromirror in place of the silicon oxide membrane.…”

Stationary Entanglement between Light and Microwave via Ferromagnetic Magnons

“…Finally, let us briefly discuss how to detect the L-M entanglement. As discussed above, the entanglement is calculated from the covariance matrix V, so we can obtain the wanted results by measuring the corresponding V. [41,[50][51][52] The state of magnon in YIG sphere can be acquired by adding an external microwave probe field through the YIG sphere and homodyning its output, while the microwave and optical field quadratures can be directly measured by homodyning their output fields too.…”

Stationary optomechanical entanglement between a mechanical oscillator and its measurement apparatus

“…There entanglement is distributed via a mediator, without the mediator ever becoming entangled (see end of Appendix A for details). Since in real experiments the light might contain some degree of classical correlations, demonstrating entanglement between certain modes of light that were mediated by a mechanical oscillator [6,7] does not allow us to make unambiguous statements regarding genuine optomechanical entanglement.…”

“…Experiments in optomechanics now operate routinely in a regime in which effects predicted by quantum theory can be observed. This includes mechanical oscillators cooled to their ground state of center-of-mass motion [1,2], ponderomotive squeezing [3][4][5], entanglement between different light tones [6,7], entanglement between different mechanical oscillators [8,9], measurement back-action [10], back-action evasion [11][12][13], and optomechanical entanglement, that is, entanglement between the mechanical oscillator and light, in a pulsed regime [14,15].…”