Two-Qubit Readout via Coupler and Tunable Resonator

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Solution Overview

Problem

Existing quantum computing systems face challenges in achieving high-fidelity readouts for qubits due to optimization tradeoffs between gate operations and measurement operations, leading to increased dephasing and leakage.

Innovation Solution

A system comprising a data qubit, a coupler coupling the data qubit to a measurement qubit, and a measurement resonator coupled to the measurement qubit, where the measurement tone applied to the measurement resonator acquires a change in phase or amplitude depending on the state of the measurement qubit, allowing for separate optimization of data and measurement qubits.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If a single qubit is used for both data storage and measurement, then the system complexity is reduced, but the optimization tradeoff between gate operations and readout operations degrades measurement precision and increases dephasing

Engineering Contradiction:

Improvequbit system structureVSAvoidreadout fidelity

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

The system divides the qubit functionality into two separate qubits: a data qubit optimized for gate operations and a measurement qubit optimized for readout operations. This segmentation allows each qubit to be independently optimized for its specific function, resolving the contradiction between system simplicity and measurement precision.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

A coupler is introduced as an intermediary component between the data qubit and measurement qubit. The coupler enables controlled interaction and state transfer between the two qubits while allowing them to be optimized independently, thus improving measurement precision without requiring the data qubit to be directly optimized for measurement.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Speed

If the data qubit is directly coupled to the measurement resonator for readout, then the readout speed is improved, but the dephasing of the data qubit increases during measurement operations

Engineering Contradiction:

Improvereadout speedVSAvoidqubit coherence

Core Design Contradiction:

SpeedVSReliability

Solution Approach 1:

The measurement qubit serves as an intermediary between the data qubit and the measurement resonator. The state information is transferred from the data qubit to the measurement qubit via the coupler, and then the measurement qubit interacts with the resonator for readout. This indirect coupling path allows fast readout while protecting the data qubit from dephasing caused by direct resonator interaction.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Device complexity

If the measurement qubit frequency is fixed, then the system complexity is reduced, but the leakage during readout operations increases

Engineering Contradiction:

Improvequbit frequency controlVSAvoidleakage during readout

Core Design Contradiction:

Device complexityVSObject-generated harmful factors

Solution Approach 1:

The measurement qubit is made frequency-tunable, allowing its frequency to be dynamically adjusted during operation. This enables optimization of the detuning between the measurement qubit and measurement resonator to minimize leakage while maintaining the ability to perform readout operations, resolving the contradiction between system simplicity and reducing harmful effects.

Inventive Principle:

Principle #15Dynamics

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 enables high-fidelity readouts by reducing dephasing and leakage, allowing for faster reuse of data qubits and improved performance of quantum computers by minimizing idle time and optimizing measurement operations.

Implementation Method 1

a measurement tone applied to the measurement resonator acquires a change in phase or in amplitude that depends on the state of the measurement qubit

Methodology Applied

Scientific EffectPhase and amplitude modulation:

Implementation Method 2

executing a measurement gate operation to entangle a data qubit to a measurement qubit, wherein the gate operation transfers measurement probabilities from the data qubit to the measurement qubit

Methodology Applied

Scientific EffectQuantum entanglement:

Data Source

PatentUS20250117682A1High fidelity readout with two qubits

Publication Date: 2025.04.10 INTERNATIONAL BUSINESS MACHINE CORPORATION

AI summary

Devices, systems and/or methods facilitating two qubit readouts are provided. In an embodiment, a system can comprise a data qubit; a coupler coupling the data qubit to a measurement qubit; and a measurement resonator coupled to the measurement qubit, wherein the measurement resonator is capable of transmitting a tone through the resonator to the measurement qubit.