Superconducting Low-Frequency Memory Resonator for Cat-Qubit Stability
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Solution Overview
Problem
Existing methods for stabilizing cat qubits face challenges in reducing the resonant frequency of the memory mode while maintaining low thermal noise and thermal population, leading to increased phase-flip probabilities and thermal noise, which are not effectively addressed by prior art solutions.
Innovation Solution
A non-linear superconducting quantum circuit with a first mode and a second mode, coupled by a non-linear element such as an ATS, operates at a resonant frequency below 3.5 GHz, utilizing a capacitive element with a capacitance of 1 to 10 pF and an inductive element with 0.3 to 5 nH, to achieve a 2-to-1 photon conversion and stabilize the cat qubit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the resonant frequency of the memory mode is reduced to lower the single-photon loss rate, then the bit-flip probability decreases exponentially, but the thermal population of the bath increases significantly
Solution Approach 1:
The patent changes the resonant frequency parameter of the memory mode from conventional high values (5-8 GHz) to a low value (3.5 GHz or lower). This parameter change simultaneously achieves exponential suppression of bit-flip probability while maintaining manageable thermal population levels, resolving the technical contradiction between reliability and thermal population quantity.
2Reliability
If the resonant frequency of the memory mode is reduced, then the single-photon loss rate decreases, but the thermal noise increases significantly
Solution Approach 1:
The patent applies parameter change by setting the resonant frequency to 3.5 GHz or lower, which reduces the single-photon loss rate exponentially while the increase in thermal noise is controlled and acceptable. This resolves the contradiction between reliability improvement and thermal noise increase.
3Reliability
If the resonant frequency of the memory mode is reduced, then the quality factor improves, but the parametric pump frequency becomes excessively high requiring excessive energy injection
Solution Approach 1:
By changing the resonant frequency parameter to 3.5 GHz or lower, the patent improves the quality factor while keeping the parametric pump frequency at manageable levels, avoiding the need for excessive energy injection that would occur with conventional high-frequency designs.
4Use of energy by moving object
If the resonant frequency of the buffer mode is reduced to lower the parametric pump frequency, then the energy injection is reduced, but the thermal population of photons in the buffer becomes too large
Solution Approach 1:
Instead of reducing the buffer mode frequency to lower the pump frequency, the patent inverts the approach by reducing the memory mode frequency to achieve low pump frequency. This inversion resolves the contradiction by avoiding excessive thermal population in the buffer while still reducing energy injection requirements.
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 solution reduces single-photon loss rates and thermal noise, enhancing the stability and fidelity of quantum gates by minimizing phase-flip probabilities without excessive thermal population, thus improving the quality factor and relaxation time of the memory mode.
Implementation Method 1
a four-wave mixing non-linear element. The non-linear element is configured to convert two photons of the first mode into one photon in the second mode
Implementation Method 2
Such a 2-to-1 photon conversion is implemented by means of a parametric pump at frequency f p = |2f a - f b |
Implementation Method 3
a specific dissipative stabilization mechanism may be performed and consists in engineering a non-linear conversion between two photons of a first mode
Data Source
Figure 1
Figure 2~3
Figure 4~5
AI summary
The invention relates to a non-linear superconducting quantum circuit including: - at least one resonant portion having a first mode with a first resonant frequency and a second mode with a second resonant frequency, and - a non-linear element (7) coupled to or at least partially included in the at least one resonant portion. The at least one resonant portion has a resonator (27) including a capacitive element (29) and an inductive element (31) together producing the first mode, the capacitive element (29) having a capacitance of between 1 and 10 pF and/or the inductive element (31) having an inductance of between 0.3 and 5 nH such that the first resonant frequency is less than or equal to 3.5 GHz.