Reconfigurable photonics with on-chip single-photon detectors

Abstract

Integrated quantum photonics offers a promising path to scale up quantum optics experiments by miniaturizing and stabilizing complex laboratory setups. Central elements of quantum integrated photonics are quantum emitters, memories, detectors, and reconfigurable photonic circuits. In particular, integrated detectors not only offer optical readout but, when interfaced with reconfigurable circuits, allow feedback and adaptive control, crucial for deterministic quantum teleportation, training of neural networks, and stabilization of complex circuits. However, the heat generated by thermally reconfigurable photonics is incompatible with heat-sensitive superconducting single-photon detectors, and thus their on-chip co-integration remains elusive. Here we show low-power microelectromechanical reconfiguration of integrated photonic circuits interfaced with superconducting single-photon detectors on the same chip. We demonstrate three key functionalities for photonic quantum technologies: 28 dB high-extinction routing of classical and quantum light, 90 dB high-dynamic range single-photon detection, and stabilization of optical excitation over 12 dB power variation. Our platform enables heat-load free reconfigurable linear optics and adaptive control, critical for quantum state preparation and quantum logic in large-scale quantum photonics applications.

Fig. 1. Device description and characterization.

a Artist view of the demonstrated device, composed of grating couplers for light input and a MEMS reconfigurable beam splitter connected to two superconducting single-photon detectors. b False-colored SEM of the input section of our device, showing the waveguides and grating couplers, and the MEMS actuator and electrodes. c Photon count rate at a wavelength of 795 nm for the two on-chip detectors and the corresponding dark counts, normalized to their individual saturated detection. The reduced critical current in the dark count measurement of detector A is due to measurement-to-measurement fluctuations in the critical current. d Measured photon detection counts versus MEMS actuation voltage, normalized to the individual maximum transmission and power ratio (PR) between detectors. Note that the detectors feature different detection efficiencies (44.6 times higher in A, see Results section).

Fig. 2. Frequency response and demonstrated applications.

a Frequency response of the tunable beam splitter measured using an on-chip detector up to the first resonance frequency normalized to the DC amplitude. The arrows represent the low bound of those measured amplitudes. Inset: this measurement was performed by translating the actuation voltage into a modulation of the splitting ratio. b PID-controlled power stabilization on one arm (detector A, orange) using the on-chip detectors and the MEMS-tunable beam splitter. The other arm (detector B, green) detects the rerouted power. The detection events are counted by the driving electronics of the detectors. c 90 dB dynamic range on-chip photodetector that combines a high and a low-efficiency detector with switchable measurement ranges. The vertical connections are the measured counts while changing the MEMS voltage from 0 V to 196.5 V. The insets show the active detectors and MEMS settings in each of the three ranges: for lowest input power, Detector A is used with most of the power routed to its waveguide. For medium input powers the MEMS splitter routes most of the optical power to lower-efficiency Detector B, and both detectors can be used. For highest optical power, no actuation is applied and low-efficiency Detector B is used.

Fig. 3. Single-photon experiments.

a Lifetime measurements using our device (purple) compared to commercial fiber–coupled SNSPDs (black). Inset: spectrum of the deterministically excited quantum dot used in this work, under π pulse excitation, with highlighted exciton (X) and biexciton (XX) lines. b HBT measurements, showing a comparison of detection off-chip (top) and detection with one SNSPD on-chip (bottom). c Sketch outlining the experimental configuration. For a the lifetime of the QD is either fully measured on-chip or using the commercial SNSPD system. For b one arm of the HBT setup is on-chip while the second arm is connected to the SNSPD system. The coincidences are then measured using a time-to-digital converter. Optical components: BS beam splitter, NF notch filter, TG transmission grating, POL polarizer, ($\frac{\lambda }{2}$) half waveplate, DUT device under test.

Fig. 4. Near-term application of our technology.

Example of a monitored and stabilized on-chip photon source as a near-term application of our technology. The device includes two power stabilizers connected to two MEMS-tunable quantum emitters and MEMS splitters for switching into an HBT/HOM monitoring circuit.