Galvanically Coupled Quantum Circuit for Cat Qubit Stabilization
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Solution Overview
Problem
Existing superconducting quantum circuits with cat qubits suffer from insufficient confinement rates and phase-flip rates, leading to inadequate bit-flip suppression times, which are crucial for practical quantum computing applications.
Innovation Solution
A non-linear superconducting quantum circuit with asymmetrical threaded superconducting quantum interference devices (ATS) galvanically connected to resonant portions, featuring distinct resonant frequencies and zero-point fluctuations above 0.05 rad, minimizing coupling element interference and enhancing two-photon conversion rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a transmon is used to engineer 2-to-1 photon conversion, then the cat qubit stabilization is achieved, but spurious cross-Kerr terms induce additional noise processes with high escape rates
Solution Approach 1:
The patent removes the transmon component from the circuit entirely, extracting the source of spurious cross-Kerr terms. Instead of using a transmon to engineer the 2-to-1 photon conversion, the invention uses a different circuit topology that achieves the same stabilization function without the harmful cross-Kerr effects, thereby eliminating the noise processes with high escape rates.
Solution Approach 2:
The patent changes the circuit parameters by using an asymmetrical threaded SQUID (ATS) with specific inductance and capacitance values that are optimized to minimize cross-Kerr terms. The ATS is configured with particular L/C ratios and coupling strengths that differ from conventional transmon designs, resulting in suppressed spurious noise processes while maintaining the desired 2-to-1 photon conversion for cat qubit stabilization.
2Measurement precision
If a transmon is used to measure the cat qubit state, then the measurement is achieved, but the bit-flip time saturates to a few milliseconds
Solution Approach 1:
The patent removes the measuring transmon from the circuit, extracting the component that causes bit-flip time saturation. The measurement function is replaced by an alternative readout mechanism that does not involve a transmon coupled to the cat qubit, thereby eliminating the source of additional noise and allowing bit-flip times to extend to hundreds of milliseconds or seconds rather than saturating at a few milliseconds.
Solution Approach 2:
The patent introduces an intermediary measurement approach that couples the cat qubit to a different type of readout device, such as a dispersive readout through a resonator or a quantum non-demolition measurement scheme. This intermediary mechanism allows state measurement without the harmful direct coupling of a transmon, preserving the long bit-flip times while enabling readout.
3Duration of action of moving object
If the ATS operates in a regime for dynamic stability, then the bit-flip time increases to 100 seconds, but the confinement rate becomes very low
Solution Approach 1:
The patent employs dynamic flux biasing of the ATS to modulate the Josephson energy and thereby control the 2-to-1 photon conversion rate dynamically. By applying a time-dependent magnetic flux through the SQUID loops, the system can switch between different operational regimes: a stable regime for long bit-flip times and a high-conversion regime for fast confinement, enabling adaptive optimization of both parameters throughout the computation.
Solution Approach 2:
The patent uses periodic parametric driving at specific frequencies to enhance the 2-to-1 photon conversion rate at desired moments. By applying periodic modulation to the ATS parameters, the system can temporarily boost the confinement rate during gate operations while maintaining long bit-flip times during idle periods, achieving both high speed and long duration through time-dependent control.
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
The circuit achieves significantly improved bit-flip suppression times, potentially up to 100 seconds, with enhanced confinement rates, surpassing previous designs by several orders of magnitude, making it suitable for practical quantum computing.
Implementation Method 1
The dissipative stabilization of two coherent states utilizes an engineering of a non-linear conversion between two photons of a first mode that hosts the stabilized quantum manifold
Implementation Method 2
asymmetrical threaded superconducting quantum interference device (also referred to as 'ATS')
Implementation Method 3
said non-linear superconducting quantum circuit has zero-point fluctuations of the superconducting phase across the asymmetrical threaded superconducting quantum interference device
Implementation Method 4
non-linear superconducting quantum circuit
Implementation Method 5
said non-linear superconducting circuit having a first mode with a first resonant frequency and a second mode with a second resonant frequency
Data Source
AI summary
A non-linear superconducting quantum circuit comprising at least one resonant portion and an asymmetrical threaded superconducting quantum interference device connected to said at least one resonant portion galvanically, said non-linear superconducting circuit having a first mode with a first resonant frequency and a second mode with a second resonant frequency, the ratio between said first resonant frequency and said second resonant frequency being different from ½, said at least one resonant portion being configured with inductance and capacitance values of its symbolic representation which induce with said asymmetrical threaded superconducting quantum interference device said first mode and said second mode such that, said non-linear superconducting quantum circuit has zero-point fluctuations of the superconducting phase across the asymmetrical threaded superconducting quantum interference device for the first mode and the second mode which are superior or equal to 0.05 rad.