Nonlinear optical effects of ultrahigh-Q silicon photonic nanocavities immersed in superfluid helium

Abstract

Photonic nanocavities are a key component in many applications because of their capability of trapping and storing photons and enhancing interactions of light with various functional materials and structures. The maximal number of photons that can be stored in silicon photonic cavities is limited by the free-carrier and thermo-optic effects at room temperature. To reduce such effects, we performed the first experimental study of optical nonlinearities in ultrahigh-Q silicon disk nanocavities at cryogenic temperatures in a superfluid helium environment. At elevated input power, the cavity transmission spectra exhibit distinct blue-shifted bistability behavior when temperature crosses the liquid helium lambda point. At even lower temperatures, the spectra restore to symmetric Lorentzian shapes. Under this condition, we obtain a large intracavity photon number of about 40,000, which is limited ultimately by the local helium phase transition. These new discoveries are explained by theoretical calculations and numerical simulations.

Proposal for an Optomechanical Bell Test

“…This frequency together with its optical linewidth κ=2π < 1 GHz places this resonator in the resolved sideband regime [45]. The optomechanical coupling rate is large g 0 =2π ≈ 1 MHz [45], and mechanical coherence times of the order of 10-100 μs are expected at 4 K and below [45,47]. With a bath temperature T bath ≈ 1.6 K, an initial occupancy of n 0 ¼ 0.01 can be achieved in 100 ns of sideband cooling with 1000 (intracavity) photons corresponding to a peak laser power of 150 μW [34].…”

Fluctuating volume-current formulation of electromagnetic fluctuations in inhomogeneous media: Incandescence and luminescence in arbitrary geometries

“…89 Temperature gradients have also been observed in atomic force microscopes 90,91 and nanowires, 92 as well as in situations involving irradiated particles immersed in fluids, 93-102 magnetic nanocontacts, 103 or microcavities subject to strong photothermal effects. 104 Material inhomogeneities also arise in microcavity lasers stemming from nonlinear effects. 105 Surprisingly, there are only a handful of calculations involving nonisothermal particles, including calculation of radiation from atomic gases in shock-layer structures with linear temperature gradients 106 or calculations of large-radii spheres based on Mie series or related semi-analytical expansions.…”

Silicon Quantum Photonics

“…Compact integrated optics can be readily fit into the confines of a cryostat, in contrast with bulk-or fibre-optic systems. Nonlinear optical effects are largely temperature-independent: χ (3) effects work nearly as well at low temperature [149]. SFWM photon-pair sources, as well as XPM and FWM, will continue to work.…”

“…Thermal-expansion-based straining, used to produce χ (2) in silicon [150], could benefit from the larger deposition-tooperation temperature difference; χ (2) and χ (3) electro-optic modulators could be invaluable for low-temperature switching. Finally, the effort expended to make silicon photonics athermal would be unnecessary: silicon's low-temperature thermo-optic coefficient is 10 000 times smaller than its room-temperature value [149], [151]. We can be optimistic that silicon photonics can accommodate either front-or back-end integrated electronics, for implementing the feedforward control required (Fig.…”