Microwave Sum Frequency Generator for Heralded Qubit Entanglement

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Solution Overview

Problem

Existing quantum communication technologies face challenges with entanglement swapping due to multipair emission from spontaneous parametric down-conversion sources, reducing fidelity and being incompatible with device-independent quantum key distribution schemes, and suffering from detection loopholes in optical tests.

Innovation Solution

A sum frequency generator in the microwave domain is used, which operates as a nonlinear filter to up-convert pairs of microwave photons to an outgoing photon with a frequency equal to the sum of the input frequencies, enabling remote entanglement of qubits and functioning as a quantum microwave repeater.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If spontaneous parametric down-conversion sources are used for entanglement swapping, then entanglement generation is achieved, but multipair emission reduces fidelity and creates detection loopholes

Engineering Contradiction:

Improveentanglement fidelityVSAvoidmultipair emission

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The patent changes the operating parameters from optical to microwave domain, using sum frequency generation instead of down-conversion. This parameter change fundamentally alters the emission characteristics, enabling single-photon operation without multipair emission while maintaining entanglement generation capability

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent substitutes the optical down-conversion mechanism with a microwave sum frequency generation mechanism. This substitution replaces the harmful multipair emission process with a controlled single-photon generation process, eliminating the fidelity issue while preserving the entanglement swapping function

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Measurement precision

If optical detection methods are used, then entanglement verification is possible, but detection loopholes remain open

Engineering Contradiction:

Improveentanglement verification accuracyVSAvoiddetection loophole

Core Design Contradiction:

Measurement precisionVSDifficulty of detecting and measuring

Solution Approach 1:

The patent substitutes optical detection with microwave domain detection. This substitution enables the use of superconducting qubits as detectors, which can perform hermetic measurements without detection loopholes, while maintaining the capability to verify entanglement through Bell inequality tests

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Reliability

If device-independent quantum key distribution is implemented, then security is enhanced, but compatibility with existing sources is poor

Engineering Contradiction:

Improvequantum key distribution securityVSAvoidcompatibility with existing sources

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The patent changes the fundamental operating parameters to microwave domain, creating new quantum light sources and detectors that are natively compatible with superconducting quantum circuits. This enables device-independent QKD protocols to be implemented with high compatibility across quantum computing platforms

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent creates a universal microwave quantum interface that can serve multiple functions: entanglement generation, entanglement swapping, quantum key distribution, and quantum computing operations. This multi-functionality ensures broad compatibility across different quantum system architectures

Inventive Principle:

Principle #6Universality (Multi-functionality)

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

This approach enhances entanglement fidelity, closes the detection loophole, and supports secure quantum communication by providing a heralded entanglement generation mechanism suitable for distributed quantum computing and device-independent quantum key distribution.

Implementation Method 1

Methodology Applied

Scientific EffectSum frequency generation: Second Harmonic Generation

Implementation Method 2

The circuit includes a first resonator connected to a Josephson ring modulator (JRM)

Methodology Applied

Scientific EffectJosephson effect: Josephson Effect

Data Source

PatentUS10345678B2Sum frequency generator in the microwave domain for quantum communication and computation applications

Publication Date: 2019.07.09 INTERNATIONAL BUSINESS MACHINE CORPORATION

AI summary

A technique relates to a circuit for a sum frequency generator. A first resonator is connected to a Josephson ring modulator (JRM), and the first resonator is configured to receive a first photon at a first frequency. A second resonator is connected to the JRM, and the second resonator is configured to have a first harmonic and no second harmonic. The second resonator is configured to receive a second photon at a second frequency, and the first resonator is configured to output an up-converted photon. The up-converted photon has an up-converted frequency that is a sum of the first frequency and the second frequency.