Photon-Number Detection for Real-Time Optical Signal Routing

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Solution Overview

Problem

Existing measurement systems for quantum computing lack intrinsic photon number resolution, hindering real-time feed-forward actions in photonic quantum computation.

Innovation Solution

Implementing photon-number resolving detectors and signal processors to determine photon numbers in real-time, using functions to generate control signals for optical signal routing through switches.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If nanowire single photon detectors or homodyne/heterodyne detectors are used for measuring quantum states, then real-time feed-forward action is enabled, but intrinsic photon number resolution is lost

Engineering Contradiction:

Improvereal-time feed-forward action capabilityVSAvoidphoton number resolution

Core Design Contradiction:

ProductivityVSMeasurement precision

Solution Approach 1:

The patent changes the detection parameter from binary detection (click/no-click) to analog signal measurement by using transition-edge sensor detectors that measure the total charge signal. This allows the system to distinguish between different photon numbers (0, 1, 2, 3 photons) while maintaining real-time operation speed, thus resolving the contradiction between measurement precision and productivity

Inventive Principle:

Principle #35Parameter changes

2Measurement precision

If photon-number resolving detectors are implemented, then intrinsic photon number resolution is achieved, but device complexity increases

Engineering Contradiction:

Improvephoton number resolutionVSAvoiddetector and processing system complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent replaces complex mechanical switching and routing systems with a digital signal processing approach. Instead of using physical switches to route signals based on photon number, the system uses an FPGA to process the analog signal traces and generate control signals, thereby reducing mechanical complexity while maintaining photon number resolution capability

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The transition-edge sensor detector serves multiple functions: it detects the presence of photons, resolves the photon number, and provides timing information all through a single analog signal output. This multi-functionality reduces the need for separate detection and counting systems, thereby reducing overall device complexity

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Loss of time

If real-time photon number determination is implemented, then optical signal routing with minimal delay is enabled, but processing time for photon number determination increases

Engineering Contradiction:

Improverouting delayVSAvoidphoton number determination speed

Core Design Contradiction:

Loss of timeVSMeasurement precision

Solution Approach 1:

The patent performs preliminary action by pre-calculating and storing reference traces for different photon numbers in the FPGA memory. When a new photon detection event occurs, the system only needs to compare the new trace against the pre-stored references using simple correlation algorithms, rather than performing complex analysis in real-time, thus reducing processing time while maintaining accuracy

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent creates a simplified digital representation (copy) of the analog signal trace by sampling it at specific time points and converting it into a discrete vector format. This digital copy can then be processed much faster through correlation with reference traces, reducing the processing time required for photon number determination while maintaining measurement precision

Inventive Principle:

Principle #26Copying

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

Enables real-time optical signal routing with minimal delay, facilitating applications in quantum computation, error correction, and entanglement heralding.

Implementation Method 1

receiving, by a signal processor, an electrical signal trace produced by a photon-number resolving detector in response to a first optical pulse

Methodology Applied

Scientific EffectPhotoelectric Effect: Photoelectric Effect

Data Source

PatentUS12574123B2Real-time photon number determination

Publication Date: 2026.03.10 XANADU QUANTUM TECHNOLOGIES HOLDINGS ULC

AI summary

Systems, methods and computer program products for real-time routing of optical signals. A signal trace is received by a signal processor from a photon-number resolving detector. The signal trace is produced by the photon-number resolving detector in response to an optical pulse from a light source (e.g. a pulsed laser). The signal processor determines the photon number of the optical pulse by applying a function to the signal trace and one or more reference traces. A feedback signal is then defined based on the photon number of the optical pulse. The feedback signal is used to control the operation of a switch positioned in the path of a related optical signal. The switch operates to define the forward routing path of the related optical signal.