Capacitive Sense Amplifier Readout for Cryogenic Spin Qubits
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Solution Overview
Problem
Existing quantum computing devices face challenges in reading qubits at cryogenic temperatures due to restrictive operating environments, which limit bandwidth, power consumption, and noise sensitivity, making it difficult to read a large number of qubits efficiently.
Innovation Solution
An electronic device with a transimpedance amplifier and capacitive feedback loop, incorporating a local common mode stabilization circuit and differential inputs, is designed to operate at cryogenic temperatures with low power consumption and high gain, enabling efficient reading of multiple qubits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If resistive feedback transimpedance amplifiers are used at low temperature, then gain is improved, but bandwidth deteriorates
Solution Approach 1:
The patent changes the feedback element from resistive to capacitive, fundamentally altering the amplifier's transfer function. The capacitive feedback loop with capacitor Cf creates a different frequency response characteristic, allowing the amplifier to achieve both high gain and wide bandwidth simultaneously by utilizing the imaginary impedance of the capacitor rather than real resistance.
Solution Approach 2:
The patent replaces the traditional resistive feedback mechanism with a capacitive feedback mechanism. This substitution changes the fundamental operating principle of the transimpedance amplifier, enabling it to overcome the bandwidth limitation inherent in resistive feedback designs while maintaining high gain performance at cryogenic temperatures.
2Object-affected harmful factors
If readout electronics are placed close to qubits at low temperature, then noise is reduced, but power consumption and size constraints worsen
Solution Approach 1:
The patent extracts the critical amplification function into a dedicated transimpedance amplifier stage with capacitive feedback, separating it from the electrometer. This allows the electrometer to operate with minimal power consumption while the amplifier, optimized for performance, handles the signal conditioning. The capacitive feedback architecture enables this separation while maintaining low overall power consumption suitable for cryogenic operation.
Solution Approach 2:
The transimpedance amplifier with capacitive feedback serves multiple functions: it provides high gain amplification, extends bandwidth, and enables reading of multiple qubits through its differential input configuration. This multi-functional design reduces the need for separate dedicated circuits for each function, thereby reducing total power consumption and component count in the cryogenic environment.
3Productivity
If a single readout circuit reads a large number of qubits, then productivity is improved, but bandwidth requirements worsen
Solution Approach 1:
The patent employs a differential amplifier configuration with two independent differential inputs, allowing parallel reading of multiple qubit sets. Each input channel can independently read multiple qubits through the electrometers, effectively segmenting the reading capacity across multiple channels while maintaining high bandwidth per channel through the capacitive feedback architecture.
Solution Approach 2:
The patent transitions from single-ended to differential signaling, adding a dimensional aspect to the readout architecture. The differential inputs and outputs create two independent signal paths, effectively doubling the reading capacity without requiring proportional increases in bandwidth for each individual channel, as the differential mode rejects common-mode noise and enables higher frequency operation.
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 device achieves high gain and bandwidth compatible with reading multiple qubits, while minimizing noise and power consumption, overcoming limitations of previous technologies.
Implementation Method 1
a transimpedance amplifier with a feedback loop, the feedback loop including at least one capacitor
Implementation Method 2
an electrometer electrostatically coupled to a potential well of the quantum dot
Data Source
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AI summary
The present description relates to a quantum electronic device (100) comprising at least: - a quantum dot (102) intended to form at least one spin qubit; - an electrometer (104) electrostatically coupled to a potential well of the quantum dot (102), comprising at least one input electrode (106) on which an excitation signal is intended to be applied and at least one output electrode (108) distinct from the input electrode (106) and on which a reading signal is intended to be delivered; - a transimpedance amplifier (116) with a feedback loop including at least one capacitor (150, 152, 154), the transimpedance amplifier (116) comprising two differential inputs (118, 120) at least one of which is coupled to the output electrode (108) of the electrometer (104), and a local common mode stabilization circuit (164, 166).