KR-20260068037-A - Non-contact Spin-state Readout Apparatus Utilizing Changes in Magnetic Susceptibility of a Single Electron within a Semiconductor Quantum Dot

Abstract

The present invention relates to a quantum computing device that reads the spin state of a single electron (140) within a semiconductor quantum dot (100) non-contactually using only a magnetic channel. The quantum dot trap section (100) isolates the single electron (140) into a potential well (130) formed by a plurality of gate electrodes (120), and the coil structure (210) of the microelectromagnet section (200) doubles as an inductor element of the LC tank circuit (310) to perform the dual application of a static magnetic field and detection of magnetic susceptibility. The change in magnetic susceptibility (Δχ) due to the spin state transition of the single electron (140) modulates the inductance (L) of the coil structure (210), and this change in inductance (ΔL) appears as a change in impedance of the magnetic impedance reading section (300). The IQ demodulator (321) of the measurement circuit (320) determines the spin state based on the amount of phase change. Sensitivity, fidelity, and scalability are comprehensively improved through superconducting kinetic inductance amplification, dual coil separation, flux-locked loop (330), parametric amplifier (340), differential dual quantum dot, frequency multiplexing array (600), Larmor synchronous stroboscopic detection, Curie law temperature correction, DNP cooperative amplification, tensor asymmetric low magnetic field reading, and reverse action shaping magnetic amplification.

Inventors

• 안범주

Assignees

• 안범주

Dates

Publication Date

20260513

Application Date

20260425

Claims (1)

1. A quantum computing device for reading the spin state of a single electron within a semiconductor quantum dot comprises: a quantum dot trap portion formed on a semiconductor substrate and isolating a single electron through a potential well formed by a plurality of gate electrodes; a microelectromagnet portion disposed adjacent to the quantum dot trap portion and including a coil structure that induces Zeeman splitting by applying a static magnetic field to the single electron by an externally applied current; an LC tank circuit that shares the coil structure of the microelectromagnet portion as an inductor element to form a resonant frequency; and a magnetic impedance reading portion including a measurement circuit that applies a probe signal to the LC tank circuit to convert and measure a change in inductance (ΔL) caused by a change in magnetic susceptibility (Δχ) into an impedance signal. A quantum computing device comprising a control unit that analyzes a signal measured by the magnetic impedance reading unit to derive quantum information of the single electron, wherein the coil structure of the microelectromagnet unit is configured to directly transmit a feedback signal to the magnetic impedance reading unit by modulating the magnetic inductance (L) by a change in magnetic susceptibility (Δχ) that occurs when the spin state of the single electron is switched to |↑> or |↓>, and wherein the reading of the spin state of the single electron is performed solely through a magnetic channel via the microelectromagnet unit without passing through a separate charge channel.

Description

Non-contact Spin-state Readout Apparatus Utilizing Changes in Magnetic Susceptibility of a Single Electron within a Semiconductor Quantum Dot The present invention relates to a quantum computing device for reading the spin state of a single electron isolated within a semiconductor quantum dot, and more specifically, to a magnetic channel type non-contact spin reading device in which magnetic susceptibility (Δχ), which changes according to the spin state transition of a single electron, modulates the magnetic inductance (L) of the coil structure (210) of the microelectromagnet part (200), and detects this change in inductance (ΔL) as a change in impedance of the LC tank circuit (310). Semiconductor spin qubit technology, which captures a single electron in a semiconductor quantum dot and utilizes its spin state as a qubit, is attracting attention as a promising candidate for next-generation quantum computing platforms due to its compatibility with silicon-based semiconductor manufacturing processes, the long coherence time of electron spins, and the potential for scale-up at the integrated circuit level. While reading single-electron spin qubits is a core technology for the practical application of quantum computing devices, the magnetic moment of a single electron spin is extremely weak at the Bohr magneton (μB) level, making direct magnetic measurement virtually impossible. Due to this fundamental difficulty, conventional spin reading technologies have relied on indirect methods that convert spin information into charge information and then measure it using a charge channel. Representative spin reading methods of conventional technology are broadly classified into three types. The first is the Energy-Selective Measurement (Elzerman reading) method, which utilizes the Zeeman Splitting Energy difference to tunnel only electrons in a spin-excited state into a storage device and detects this tunneled charge using a Quantum Point Contact (QPC) or Single Electron Transistor (SET). This method requires a strong magnetic field condition of gμBB >> kBT and poses a significant barrier to scale-up as it requires a separate QPC or SET device and dedicated wiring for each qubit. The second is a reading method utilizing Spin-Charge Coupling Resonance, which induces spin-charge hybridization transitions by applying microwaves in a slanting magnetic field environment generated by microelectromagnets and detects the resulting charge fluctuations using a QPC. This method has limitations in that the detection target is still charge and detection is possible only under resonance conditions. The third method is Dispersive Gate Sensing, in which an RF resonant circuit is connected to the gate electrode to detect changes in quantum capacitance (ΔC) caused by the tunneling of a single electron as a phase change of the reflected signal. In this method, the detection channel is the change in capacitance (ΔC), and the inductance of the LC circuit is a fixed passive component that does not contribute to signal generation. A common limitation of these conventional technologies is that the detection channel is based on changes in charge or capacitance and does not directly detect the magnetic properties of a single electron spin. Consequently, a spin-charge conversion step is necessarily interposed between the physical signal source for spin reading and the detection mechanism, inevitably leading to errors and a degradation of qubit coherence during the conversion process. Although nano-SQUID (nano-Superconducting Quantum Interference Device) technology possesses the sensitivity to directly detect the magnetic signals of a single electron spin, it utilizes a scanning probe fabricated at a sharp tip, making on-chip integration with semiconductor quantum dot devices impossible. Therefore, no on-chip integrable device capable of non-contact spin state reading using only a magnetic channel has yet been presented, and a technical need for such a device exists. FIG. 1 is a block diagram of the overall system configuration of a magnetic susceptibility-based non-contact spin reading device according to one embodiment of the present invention. FIG. 2 is a cross-sectional view of a quantum dot trap section and a microelectromagnet coil structure according to one embodiment of the present invention. FIG. 3 is a detailed view of a double coil structure according to one embodiment of the present invention. FIG. 4 is a circuit diagram of a magnetic impedance reading unit according to one embodiment of the present invention. FIG. 5 is a block diagram of a magnetic flux locking loop and a graph of the operating point holding characteristic according to one embodiment of the present invention. FIG. 6 is a planar layout of a differential dual quantum dot configuration according to one embodiment of the present invention. FIG. 7 is a configuration diagram of a frequency multiplexed multi-qubit array according to one embodiment of the present invention. F