Superconducting Resonator Quantum State Measurement

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Solution Overview

Problem

Existing methods for measuring the quantum state of superconducting resonators often alter the state undesirably and are cumbersome, particularly when using DC SQUID for readout.

Innovation Solution

A system and method involving a nonlinear resonator coupled to input and output ports, excited with a signal to measure phase shifts, allowing calculation of the quantum state without altering it, using microwave readout and scattering parameters.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If dispersive readout or DC SQUID transfer methods are used to measure resonator state, then measurement capability is achieved, but the quantum state is altered undesirably and the process is time-consuming

Engineering Contradiction:

Improvequantum state measurement accuracyVSAvoidmeasurement time

Core Design Contradiction:

Measurement precisionVSLoss of time

Solution Approach 1:

The patent introduces a qubit as an intermediary system that interacts with the resonator through controlled coupling. The qubit serves as a mediator to transfer quantum information from the resonator without direct measurement of the resonator state, enabling indirect measurement that preserves the resonator's quantum state while achieving measurement through the qubit's state changes.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent replaces the traditional DC SQUID mechanical measurement system with a quantum mechanical approach using qubit-based dispersive readout. Instead of direct electrical measurement that collapses the wavefunction, the system uses quantum state transfer and interference effects to measure the resonator state indirectly, reducing measurement time and preserving quantum coherence.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Reliability

If DC SQUID transfer method is used, then quantum state can be read, but the process becomes cumbersome and time consuming

Engineering Contradiction:

Improvequantum state readout reliabilityVSAvoidmeasurement system complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent merges the resonator and qubit into a coupled quantum system where the qubit serves dual purposes: as the measurement probe and as part of the resonant circuit. This integration allows the measurement function to be embedded within the quantum circuit itself, simplifying the overall system architecture compared to separate DC SQUID measurement apparatus.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The qubit-based measurement system provides multi-functionality by enabling both quantum state transfer and measurement within a single circuit architecture. The same qubit that participates in quantum computations also serves as the readout probe, eliminating the need for separate dedicated measurement devices and reducing system complexity.

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

Enables precise determination of the quantum state of superconducting resonators without changing their state, improving efficiency and reducing measurement time.

Implementation Method 1

measuring a phase shift of the signal at an output port of the circuit

Methodology Applied

Scientific EffectPhase shift measurement:

Data Source

PatentUS8117000B2Measuring quantum states of superconducting resonators

Publication Date: 2012.02.14 INTERNATIONAL BUSINESS MACHINE CORPORATION

AI summary

A method for measuring the quantum state of a resonator includes, exciting an input port of a circuit with signal, measuring a phase shift of the signal at an output port of the circuit, wherein the resonator is coupled to the input and the output ports, and calculating a quantum state of the resonator as a function of the measured phase shift of the signal.