Driven Resonator ZZ Cancellation in Superconducting QPU

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Solution Overview

Problem

Existing superconducting quantum computing systems face challenges in mitigating coherent errors caused by stray ZZ interactions between qubits, which limit the fidelity of both single and two-qubit gates.

Innovation Solution

A quantum computing system employing a high-coherence microwave resonator to cancel unwanted ZZ coupling via resonator-induced-phase (RIP) interaction, using a drive resonator to induce entanglement between control and target qubits at a ZZ-free operating point.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If coupling strength between qubits is increased to enable faster entangling operations, then gate speed is improved, but stray ZZ interactions increase causing coherent errors

Engineering Contradiction:

Improvegate speedVSAvoidcoherent errors from ZZ interactions

Core Design Contradiction:

SpeedVSObject-affected harmful factors

Solution Approach 1:

The patent applies AC Stark shifting to convert the harmful ZZ interaction into a beneficial effect. By driving the qubits with microwave pulses at specific frequencies, the AC Stark shift creates a dynamic energy shift that cancels the static ZZ coupling, transforming the harmful interaction into a tool for error mitigation while enabling stronger coupling for faster gates

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The patent changes the energy parameters of the qubit system dynamically through AC driving. By adjusting the drive frequency and amplitude, the system experiences time-dependent energy shifts that compensate for the ZZ interaction, allowing the system to operate at stronger coupling strengths without suffering from coherent errors

Inventive Principle:

Principle #35Parameter changes

2Reliability

If flux-tunable couplers are introduced to mitigate ZZ interactions, then gate fidelity is improved, but decoherence errors increase due to high loss rates

Engineering Contradiction:

Improvegate fidelityVSAvoiddecoherence errors

Core Design Contradiction:

ReliabilityVSLoss of energy

Solution Approach 1:

The patent replaces the mechanical/flux-based tuning approach with an electromagnetic field-based AC driving approach. Instead of using flux-tunable couplers that physically alter the system, the patent uses microwave drives to create virtual energy shifts, eliminating the need for additional lossy components while achieving the same fidelity improvement

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Object-affected harmful factors

If multi-path couplers or AC Stark shifts are used to suppress ZZ interaction, then coherent errors are reduced, but device complexity increases

Engineering Contradiction:

Improvecoherent errorsVSAvoidcontrol complexity

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The patent makes the AC driving system multi-functional by using the same microwave drive infrastructure for both gate operations and ZZ cancellation. The drive system serves dual purposes: implementing entangling gates and simultaneously suppressing ZZ interactions through AC Stark shifting, thereby reducing overall device complexity despite the advanced error mitigation capability

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 effectively cancels static ZZ coupling, allowing for stronger qubit coupling without introducing coherent errors, thereby improving the fidelity of entangling gates and reducing gate times.

Implementation Method 1

a high-coherence microwave resonator to cancel unwanted ZZ coupling via resonator-induced-phase (RIP) interaction

Methodology Applied

Scientific EffectResonator-induced-phase (RIP) interaction: Resonance

Implementation Method 2

The resonator device may be in a displaced vacuum state during the controlled phase

Methodology Applied

Scientific EffectResonance: Resonance

Data Source

PatentUS20250139485A1Systems and methods of ZZ cancellation using a driven resonator in a superconducting quantum processor unit

Publication Date: 2025.05.01 FERMI FORWARD DISCOVERY GROUP LLC

AI summary

A superconducting quantum processor unit (QPU) comprising a resonator having a resonator frequency ωC coupled between a control qubit having a control frequency ωL and a target qubit having a target frequency ωR. The control frequency ωL is detuned from the target frequency ωR at less than a detuning gap of the resonator frequency ωC. A microwave drive applies to the resonator a resonator drive frequency ωcd at a drive strength substantially equal to a ZZ-free operating point 0 of a controlled phase for the control qubit, resonator, and target qubit to induce entanglement between the control and target qubits. The effective ZZ coupling between the control and target qubits vanishes at operating point 0. The resonator may be of either a 2D or a 3D high-coherence resonator type. Control and target qubits may be of a fixed-frequency transmon type (e.g., cross-resonance (CR) Controlled-NOT (CNOT) or adiabatic Controlled-Z (CZ)).