Spin Qubit Impedance Readout With Integrated Cryogenic LC Circuit
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Solution Overview
Problem
Current quantum computing technologies face challenges in integrating readout electronics at low temperatures due to conduction losses and the use of bulky discrete components, which limits the number of qubits that can be integrated and affects sensitivity and resonance frequency.
Innovation Solution
A quantum device with integrated data and measurement qubits, an inductor, and a voltage amplifier formed in a semiconductor layer, operating at cryogenic temperatures, which uses an LC circuit for impedance measurement to read the quantum spin state without bulky discrete components, reducing parasitic capacitances and increasing integration density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If readout electronics are placed at room temperature with cables connecting to qubits in cryostat, then reading operation is simple, but conduction losses increase and minimum temperature of cryostat is limited
Solution Approach 1:
The patent transitions the readout electronics from room temperature (one temperature dimension) to cryogenic temperatures (another temperature dimension), placing them inside the cryostat near the qubits. This dimensional change in temperature placement eliminates long cable connections and reduces conduction losses while maintaining reading functionality.
Solution Approach 2:
The patent merges the readout electronics with the qubit system by placing both within the same cryogenic environment and integrating their connections. This combining eliminates the need for separate room-temperature electronics and long interconnection cables, thereby reducing energy losses.
2Measurement precision
If additional devices (SET or quantum reservoir) are used for reading, then spin-to-charge conversion is achieved, but number of qubits that can be integrated per unit area decreases
Solution Approach 1:
The patent makes the qubit itself multi-functional by enabling it to serve both as the quantum information storage unit and as its own readout device through direct impedance measurement. This eliminates the need for separate SETs or quantum reservoirs, freeing up space for more qubits per unit area while maintaining precise spin reading capability.
Solution Approach 2:
The patent extracts the readout function from separate additional devices (SETs, quantum reservoirs) and integrates it directly into the qubit system through impedance measurement of the qubit's own resonant frequency. This removal of extra components increases integration density.
3Measurement precision
If macroscopic components (directional couplers, discrete inductors) are used for reflectometry, then reading is achieved, but parasitic capacitances increase and sensitivity is limited
Solution Approach 1:
The patent replaces the mechanical/electrical system of macroscopic components (directional couplers, discrete inductors, cables) with a miniaturized integrated circuit system operating at cryogenic temperatures. This substitution eliminates parasitic capacitances associated with large components and long connections, improving sensitivity.
Solution Approach 2:
The patent nests the readout electronics within the same integrated circuit substrate as the qubits, placing both within the cryostat. This nesting arrangement minimizes interconnection lengths and eliminates the need for external macroscopic components, thereby reducing parasitic effects and improving sensitivity.
4Measurement precision
If inductor and capacitor are integrated in same substrate, then parasitic capacitances are reduced, but manufacturing complexity increases
Solution Approach 1:
The patent merges the inductor and capacitor onto the same integrated circuit substrate, forming an LC resonant circuit that is co-integrated with the qubits. This combining reduces parasitic capacitances from interconnections while the integrated manufacturing approach manages production complexity through standardized processes.
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
Enables high integration density and improved capacitive sensitivity by integrating all readout electronics within the same circuit, reducing interconnection lengths and parasitic capacitances, thus enhancing the sensitivity and control of the quantum device's operating frequency.
Implementation Method 1
an inductor (104) coupled in parallel or in series to a gate of one or more measurement qubits (102), such that the inductance (104) and the capacitance formed by the gate(s) of the measurement qubit(s) (102) form an LC circuit
Implementation Method 2
Reading quantum spin uses a spin-to-electric-charge or motion-to-charge (capacitance) conversion process, followed by detection of the resulting electric charge
Data Source
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AI summary
A quantum device (100) with spin qubits, comprising: - a data qubit and a measurement qubit (102) made in a semiconductor layer and coupled to each other by a tunnel junction made in the semiconductor layer, each comprising a quantum dot and a control gate; - an inductance coupled to the gate of one of the qubits or to another gate capacitively coupled to one of the qubits, the inductance and a capacitance formed by said gate forming an LC circuit; - a first input terminal (122) coupled to the LC circuit and receiving a periodic control voltage of frequency fr substantially equal to the resonance frequency of the LC circuit; - a voltage amplifier (112) comprising an input coupled to the gate to which the inductance is coupled; - an output terminal coupled to an output of the amplifier.