RU2641621C2 - Ultrafast and ultrasensitive hybrid superconducting waveguide single-photon detector with low dark count rate - Google Patents

Abstract

FIELD: physics.SUBSTANCE: ultrafast and ultrasensitive hybrid superconducting waveguide single-photon detector with a low dark count rate includes a sensitive nanowire from a superconducting NbN film located on a nanowave guide SiN, and a protective dielectric-metallic coating consisting of an SiOdielectric layer and a layer of Al metal deposited over the nanowire.EFFECT: providing the possibility of reducing false triggering of a superconducting single-photon waveguide detector and increasing the sensitivity of the superconducting single-photon waveguide detector.3 dwg

Description

The invention relates to devices for detecting single photons in the visible and infrared ranges and can be used in optical fiber communication systems over long distances, in telecommunication technologies, in integrated optics and nanophotonics systems, in the protection of transmitted information using quantum cryptography systems, in diagnostics and testing of large integrated circuits (LSI) in electronics, in the spectroscopy of single molecules, in the analysis of quantum dot radiation in semiconductor nanostructures structures, in astronomy, medicine, in the development of quantum computers and in the IT field of optical processors.

Patent search was carried out by keywords and IPC categories by countries: USA, Russia, Japan, European Community. When conducting a patent search, the websites of the countries of search and the patent fund of the Federal Service for Intellectual Property, Patents and Trademarks were used.

From open sources, Patent US 6218657 (published 04.17.2001, G01J 1/46) was found, which proposes to use an avalanche photodiode in shutter mode to detect an optical pulse containing a small number of photons as part of a quantum cryptographic system.

The parameters of semiconductor avalanche photodiodes do not allow reaching extremely low error values of quantum cryptographic systems, in contrast to the proposed systems based on superconducting single-photon SSPD detectors.

US patent 7616904 B1 (published on July 28, 2011, G01J 1/36, G02B 6/10). Germanium in a silicon waveguide located on a silicon / insulator substrate. A photodetector is embedded in a silicon planar waveguide on a substrate. The photodetector generates an electric current when infrared radiation of the signal passes through the photodetector.

The implementation of such a scheme is fraught with fundamental technological difficulties that do not allow achieving acceptable indicators of quantum efficiency, speed and speed of dark counting.

Patent WO 2014026724 A1 (published on 02.20.2014; G01J 1/36, G02B 6/10) is a spectrometer with a single-photon superconductor detector on a single chip. The invention describes an integrated hybrid of a nanophotonic superconductor device that operates as a scanning spectrometer with single-photon resolution and picosecond time resolution. The device is implemented on a single chip and is optically connected using optical fibers, thus compatible with the optical image system via matching fiber ports.

The closest analogue is described in patent US 20140299751 A1 (09.10.2014, G02B 6/02, G01J 1/04, G02B 6/12) - a single-photon superconducting detector on a dielectric waveguide. The invention describes an integrated hybrid nanophotonic superconductor device that operates as a counter of single photon telecommunication wavelengths propagating inside a dielectric waveguide.

The closest analogue of the invention includes a silicon substrate with a SiO ₂ sublayer, Si ₃ N ₄ nanowaveguide (see Fig. 1). Two nanowires are parallel to each other along the nanowave directly on it. A nanowire is a photosensitive strip 100 nm wide, made of a 4 nm thick NbN superconductor film. To remove the signal, gold contact pads are fed to the nanowires (see Fig. 2).

In the operating mode, the detector has a temperature below the temperature of the superconducting transition (for example, the temperature of liquid helium is 4.2 K).

When a photon is absorbed by a superconductor, a Cooper pair is destroyed. Superconductivity is suppressed for a short time in a small part of the strip compared to the width, and a "hot spot" is formed. In this area, a resistance appears, the value of which corresponds to the resistance of the film from which the strip is made, in the normal state. If at this time a current close to the critical depairing current is passed through the strip, then it redistributes over the part of the film remaining in the superconducting state, and the current density in the superconducting region begins to exceed the critical value. As a result, the entire cross section of the strip goes into a normal state, and an electrical resistance appears in the detector, which is accompanied by a voltage pulse.

As in the closest analogue, in order to obtain high sensitivity in the visible and infrared wavelength ranges, the sensitive element is a strip of a thin film of NbN superconductor going back and forth along the nanowave. The thickness of the strip film is of the order of the coherence length, and the strip width is less than the penetration depth of the magnetic field.

At the indicated strip size, the critical current Ic is about 20 μA at a temperature of 4.2 K. The value of the transport current is 0.8-0.9 of Ic.

The main disadvantage of the closest analogue of the invention is that, due to the topology used in the invention, the detector has a high speed dark counting. High dark counting speed results from the following:

1. Own noise of the detector - false alarms, which are explained by the very principle of the detector.

2. Internal noise of electronic equipment.

3. Dark alarms can occur due to background radiation from the heated internal parts of the cryogenic reservoir, which directly hits the detector, bypassing the nanowaveguide.

The main contribution to the speed of the dark counting is made by background radiation, therefore, the solvable task of the invention is to protect the sensitive part of the superconducting single-photon detector from the background radiation of the heated internal parts of the cryogenic reservoir.

The technical result is:

- reduction of dark (false) responses of a superconducting single-photon waveguide detector;

- increase the sensitivity of a superconducting single-photon waveguide detector.

New in the developed method is that a protective dielectric-metal coating (Fig. 3) of a superconducting single-photon waveguide detector is used to reduce dark responses. As the main materials, the dielectric-metal coating uses a dielectric SiO ₂ and metal Al.

Claims (1)

An ultra-fast and ultra-sensitive hybrid superconducting nanowaveguide single-photon detector with a low dark count rate, including a sensitive nanowire of a NbN superconductor film located on a Si ₃ N ₄ nanowave, and a protective dielectric-metal coating consisting of a SiO ₂ dielectric layer and an Al metal layer, deposited over the nanowire.

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