Perfect continuous-variable quantum microcombs

Abstract

Quantum microcombs generated in high-Q microresonators provide compact, multiplexed sources of entangled modes for continuous-variable (CV) quantum information processing. While deterministic generation of CV states via Kerr-induced two-mode squeezing has been demonstrated, achieving spectrally uniform squeezing remains challenging because of asymmetry and anomalies in the dispersion profile. Here we overcome these limitations by combining a microresonator with an engineered mode spectrum and optimized pump conditions. We realize a CV quantum microcomb comprising 14 independent two-mode squeezed states, each exhibiting more than 4 dB of raw squeezing (up to 4.3 dB) across a 0.7 THz bandwidth. This uniform, high-performance quantum resource represents a key step toward scalable, integrated CV quantum technologies operating beyond classical limits.

Figures (6)

• Figure 1: Mode structure and quantum correlations in a CV quantum microcomb. Schematic integrated dispersion of a microresonator, showing the distribution of optical modes and the corresponding frequency-multiplexed qumodes used for two-mode squeezing. Gray shaded regions indicate modes strongly perturbed by avoided mode crossings (AMXs), where dispersion asymmetry degrades quantum correlations.
• Figure 2: Spectrally purified microresonator. (a) Scanning electron micrograph of a silica microdisk with a 10 $\mu$m-wide Al ring deposited near the disk edge. (b) Transmission spectrum of the fundamental transverse mode family. Inset: simulated mode profile in the disk cross section. (c) Integrated dispersion of the fundamental family without (i) and with (ii) the Al ring. The metal ring selectively damps higher-order families and yields an AMX-free window around 1543.2 nm.
• Figure 3: Experimental setup. CW laser: continuous-wave laser; EO comb: electro-optic comb; EDFA: erbium-doped fiber amplifier; PM/IM: phase/intensity modulators; BPF: band-pass filter; PC: polarization controller; BS: beam splitter; HR: highly reflective mirror; PD: photodetector; BPD: balanced photodetector; ESA: electrical spectrum analyzer; FPGA: field-programmable gate array.
• Figure 4: CV microcomb with and without AMX. (a,b) Measured integrated dispersion near 1546.2 nm (AMX near $k=-24$) and 1543.2 nm (AMX-free). (c,d) Shot-noise–normalized two-mode quadrature variances for EPR pairs at the two pump wavelengths. (e) Representative homodyne traces at 0.5 MHz (resolution bandwidth 100 kHz, video bandwidth 10 Hz, 2.4 s sweep) for $(11,-11)$, $(16,-16)$, $(21,-21)$, $(23,-23)$, and $(25,-25)$. Electronic noise of the photodetector is subtracted; the shot-noise level is shown in gray.
• Figure 5: Parametric control of the microcomb bandwidth. (a) Normalized detunings $\zeta_k$ of different qumodes for three pump detunings: $\zeta_0=\alpha$ (A), $\zeta_0=\alpha/2$ (B), and $\zeta_0=0$ (C). (b) Simulated shot-noise–normalized quadrature-noise variances at $\alpha=0.8$ for $\zeta_0=0.8$ (A), $0.4$ (B), and $0$ (C). (c) Measured quadrature-noise variances for the same operating points as in (b). Inset: transmission spectra at pump powers of 29 $\mu$W (B) and 39 $\mu$W (C); the operating points are indicated by circles.