DC Voltage Bias Stabilizes Cat Qubit
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Solution Overview
Problem
The existing methods for stabilizing cat qubits face limitations due to the proportional relationship between the two-photon coupling rate and the amplitude of the parametric pump, which restricts the enhancement of the 2-to-1 photon conversion without introducing parasitic effects.
Innovation Solution
A quantum system comprising a non-linear superconducting quantum circuit with a non-linear element, including at least one Josephson junction, and a command circuit with a microwave source and a DC voltage source. The system stabilizes a cat qubit by delivering microwave radiation and DC voltage to induce a microwave oscillation, allowing for a higher two-photon coupling rate without the limitations of the parametric pump amplitude.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the amplitude of the parametric pump is increased to enhance the two-photon coupling rate, then the stabilization of the cat qubit is improved, but parasitic effects associated with harmonics of the AC pump are introduced
Solution Approach 1:
The patent changes the fundamental parameter of pump delivery from AC (time-varying) to DC (constant). This parameter change eliminates the harmonics issue entirely while maintaining the ability to achieve the desired microwave oscillation frequency through the Josephson junction's non-linear response, thus resolving the contradiction between stabilization quality and parasitic effects
Solution Approach 2:
The patent substitutes the AC parametric pump mechanism with a DC voltage bias mechanism. Instead of using time-varying electromagnetic pumping, a constant DC voltage is applied to the Josephson junction, which then generates the required microwave oscillation at frequency |2f_a - f_b| through its non-linear current-phase relationship, eliminating the harmonic parasitics inherent in AC pumping
2Productivity
If the two-photon coupling rate is increased to improve stabilization, then the efficiency of photon conversion is enhanced, but the system becomes more sensitive to parasitic effects
Solution Approach 1:
The patent changes the operating regime from AC parametric pumping to DC voltage biasing. This parameter change allows the two-photon coupling rate to be enhanced through the DC-induced microwave oscillation without the system becoming sensitive to parasitic effects, since DC biasing inherently eliminates the harmonics that cause such sensitivity
3Reliability
If a parametric pump is used to enable four-wave mixing, then the non-linear conversion is achieved, but the coupling rate is limited by the pump amplitude
Solution Approach 1:
The patent substitutes the AC parametric pump with a DC voltage source combined with the Josephson junction's non-linear element. This substitution removes the amplitude limitation inherent in AC pumping, as the DC bias can be increased without generating harmful harmonics, thereby enhancing the two-photon coupling rate while maintaining four-wave mixing capability
Solution Approach 2:
The patent changes the pumping parameter from AC amplitude (which is limited) to DC voltage (which can be scaled). This parameter change removes the coupling rate limitation, as the DC voltage can be adjusted to achieve the desired oscillation frequency and coupling strength without the constraints of AC parametric pumping
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 proposed solution effectively increases the two-photon coupling rate, enhancing the stabilization of cat qubits while avoiding parasitic effects associated with the harmonics of the AC pump, thereby improving the robustness and efficiency of the stabilization process.
Implementation Method 1
The non-linear element including at least one Josephson junction, the non-linear element being coupled to the first resonant portion and the second resonant portion
Implementation Method 2
the microwave source delivers microwave radiation at a frequency substantially equal to the second resonant frequency to the second resonant portion to drive the second mode
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
The invention relates to a quantum system (1) for stabilizing a cat qubit comprising: - a command circuit (5) including a microwave source (11) and a DC voltage source (13), and - a non-linear superconducting quantum circuit (3) including a non-linear element (7) comprising a Josephson junction, a first and a second resonant portions respectively having a first mode with a first resonant frequency fa and a second mode with a second resonant frequency fb. The non-linear superconducting quantum circuit (3) stabilizes a two-dimensional manifold hosting the cat qubit when: • the microwave source (11) delivers microwave radiation at a frequency equal to fb to the second resonant portion to drive the second mode, and • the DC voltage source (13) delivers DC voltage to bias the non-linear element (7), with the delivered DC voltage having a value inducing a microwave oscillation having a frequency equal to |2fa - fb|.