BACKGROUND

Photonic integrated circuits having high sensitivity, such as single photon detectors, may be used in many photonic quantum technologies, such as quantum cryptography and quantum computing. One class of single photon detectors are superconducting nanowire single photon detectors (SNSPDs). An SNSPD includes a nanowire and can detect photons based on the transition of the nanowire from a superconductive state to a resistive state upon absorption of a single photon. For the nanowire to be in the superconductive state, it may need to operate in a low temperature environment, such as at a cryogenic temperature (e.g., less than about 5 Kelvin).

SUMMARY

Techniques disclosed herein relate generally to cooling a photonic integrated circuit, such as a superconducting nanowire single photon detector, to low temperatures, such as cryogenic temperatures. In one embodiment, a device may include a substrate, a dielectric layer on the substrate, an optical waveguide in the dielectric layer, a superconducting circuit in the dielectric layer and coupled to the optical waveguide, and a micro-channel in the dielectric layer and adjacent to the superconducting circuit. The micro-channel may be aligned with the superconducting circuit and may conduct a liquid at a cryogenic temperature to locally cool the superconducting circuit. Various inventive embodiments are described herein, including methods, processes, systems, devices, and the like.

In some embodiments, the superconducting circuit may include a photosensitive nanowire. In some embodiments, the photosensitive nanowire may include a niobium nitride nanowire, a niobium germanium nanowire, or a niobium titanium nitride nanowire. The superconducting circuit and the optical waveguide may be parts of a single-photon detector. The superconducting circuit may be characterized by a superconducting temperature at or below 4 kelvin and/or a thickness less than 10 nm. A distance between the micro-channel and the superconducting circuit may be less than 1 μm. The micro-channel may have a cross-sectional area greater than 10 μm2and may be characterized by a width that is at least twice of a width of the superconducting circuit.

In accordance with some embodiments, a method may include fabricating a device including a first dielectric layer, an optical waveguide in the first dielectric layer, and a superconducting circuit in the first dielectric layer and on the optical waveguide; forming a sacrificial structure on the first dielectric layer and aligned with the superconducting circuit; depositing a second dielectric layer on the sacrificial structure; cutting an opening in the second dielectric layer to expose the sacrificial structure; wet etching the sacrificial structure through the opening; and sealing the opening in the second dielectric layer with a third dielectric layer to form a micro-channel between the first dielectric layer and the second dielectric layer.

In some embodiments, the superconducting circuit may be characterized by a thickness less than 10 nm, a distance between the micro-channel and the superconducting circuit may be less than 1 μm, and a width of the micro-channel may be at least twice of a width of the superconducting circuit. In some embodiments, the method may also include etching the second dielectric layer and the third dielectric layer to form a deep trench in the device and to expose an input port of the micro-channel, bonding a base plate to a carrier, and bonding the device to the base plate in the carrier. In some embodiments, the base plate may include a channel and a deep trench, and the deep trench in the base plate may be aligned with the deep trench in the device.

According to certain embodiments, a system may include a housing including an input port and an output port, a base plate in the housing and including a first micro-channel connected to the input port of the housing, and a photonic integrated device bonded to the base plate. The photonic integrated device may include a superconducting circuit, a second micro-channel adjacent to and aligned with the superconducting circuit and connected to the output port of the housing, and a trench in fluidic communication with the input port of the housing through the first micro-channel and in fluidic communication with the output port of the housing through the second micro-channel. The first micro-channel, the trench, and the second micro-channel may be configured to conduct a liquid at a cryogenic temperature from the input port to the output port of the housing.

In some embodiments, a distance between the second micro-channel and the superconducting circuit may be less than 1 μm. The base plate may include a silicon substrate. In some embodiments, the base plate may include a cut-out region aligned with the trench in the photonic integrated device, the cut-out region and the trench forming a reservoir for storing the liquid at the cryogenic temperature. In some embodiments, the photonic integrated device may be fusion-bonded to the base plate to form a sealed conduit from the input port to the output port of the housing. In some embodiments, the housing may include a ceramic package. In some embodiments, the photonic integrated device may also include an optical waveguide adjacent to and aligned with the superconducting circuit, the optical waveguide and the superconducting circuit forming parts of a superconducting nanowire single photon detector.

Numerous benefits can be achieved by way of the present invention over conventional techniques. For example, techniques disclosed herein can be used to locally cool a particular circuit in a system, where only the particular circuit needs to operate at very low temperature, such as cryogenic temperatures, rather than globally cooling the whole system. Therefore, the cooling techniques disclosed herein can increase cooling efficiency and speed, reduce coolant and energy consumption, and allow the system to operate at higher ambient temperature with local cold spots.

