US-20260127470-A1 - PREVENTION OF QUBIT DECOHERENCE USING ACTIVE FEEDBACK CIRCUITS

US20260127470A1US 20260127470 A1US20260127470 A1US 20260127470A1US-20260127470-A1

Abstract

Disclosed are systems and techniques to improve coherence of qubits experiencing fluctuating electric potential caused by the environment. In some implementations, a processing device implementing the disclosed techniques includes a first (second) qubit structure formed using a first (second) set of electrodes electrostatically confining a first (second) electron in a direction lateral to a film, the film including a condensed phase of one or more inert gas elements. The processing device further includes a feedback circuitry to subject the first qubit structure to a probe signal, receive a response signal caused by an interaction of the probe signal with the first qubit structure, generate, using the response signal, a correction signal, and subject the first qubit structure and the second qubit structure to the correction signal.

Inventors

Gerwin Koolstra
Elena O. Glen

Assignees

EEROQ CORPORATION

Dates

Publication Date: 20260507
Application Date: 20241029

Claims (20)

1 . A processing device comprising: a first qubit structure formed using a first set of electrodes electrostatically confining a first electron in a direction lateral to a film, wherein the film comprising a condensed phase of one or more inert gas elements; a second qubit structure formed using a second set of electrodes electrostatically confining a second electron in the direction lateral to the film; a feedback circuitry to: subject the first qubit structure to a probe signal; receive a response signal caused by an interaction of the probe signal with the first qubit structure; generate, using the response signal, a correction signal; and subject the first qubit structure and the second qubit structure to the correction signal.
2 . The processing device of claim 1 , wherein the first electron and the second electron are confined, in a direction perpendicular to the film, by electrostatic forces of attraction to at least one of (i) the film or (ii) one or more electrodes located below the film.
3 . The processing device of claim 1 , wherein each of the first qubit structure and the second qubit structure comprises a resonator circuit.
4 . The processing device of claim 3 , wherein the resonator circuit has a resonance frequency in at least one of a radio frequency range or a microwave range, and wherein the resonance frequency corresponds to a difference between an excited state energy of the first electron and a ground state energy of the first electron.
5 . The processing device of claim 1 , wherein the probe signal comprises at least one of: a continuous in time signal; or a pulsed signal.
6 . The processing device of claim 5 , wherein the probe signal comprises the continuous in time signal having a frequency that corresponds to a resonant frequency of the first qubit structure.
7 . The processing device of claim 1 , wherein the feedback circuitry comprises a mixer to: receive the response signal and a copy of the probe signal; and generate an intermediate signal representative of a phase difference between the response signal and the copy of the probe signal, the phase difference representative of noise of a resonant frequency of the first qubit structure.
8 . The processing device of claim 7 , wherein the feedback circuitry further comprises a proportional-integral-derivative (PID) controller to: generate the correction signal, wherein the correction signal is generated using the intermediate signal and a reference signal.
9 . The processing device of claim 8 , wherein the correction signal generated by the PID controller is configured to reduce a difference between the intermediate signal and the reference signal.
10 . The processing device of claim 1 , wherein the one or more inert gas elements comprise helium.
11 . A method comprising: subjecting a first qubit structure to a probe signal, wherein the first qubit structure is formed by a first set of electrodes electrostatically confining a first electron in a direction lateral to a film, wherein the film comprising a condensed phase of one or more inert gas elements; receiving a response signal caused by an interaction of the probe signal with the first qubit structure; generating, using the response signal, a correction signal; and subjecting the first qubit structure and a second qubit structure to the correction signal, wherein the second qubit structure is formed using a second set of electrodes electrostatically confining a second electron in the direction lateral to the film.
12 . The method of claim 11 , wherein the first electron and the second electron are confined, in a direction perpendicular to the film, by electrostatic forces of attraction to at least one of (i) the film or (ii) one or more electrodes located below the film.
13 . The method of claim 11 , wherein each of the first qubit structure and the second qubit structure comprises a resonator circuit.
14 . The method of claim 13 , wherein the resonator circuit has a resonance frequency in at least one of a radio frequency range or a microwave range, and wherein the resonance frequency corresponds to a difference between an excited state energy of the first electron and a ground state energy of the first electron.
15 . The method of claim 11 , wherein the probe signal comprises at least one of: a continuous in time signal, or a pulsed signal.
16 . The method of claim 15 , wherein the probe signal comprises the continuous in time signal having a frequency that corresponds to a resonant frequency of the first qubit structure.
17 . The method of claim 11 , wherein generating the correction signal comprises: receiving the response signal and a copy of the probe signal; and generating, using a mixer, an intermediate signal representative of a phase difference between the response signal and the copy of the probe signal, wherein the phase difference is representative of noise of a resonant frequency of the first qubit structure.
18 . The method of claim 17 , further comprising: processing, using a proportional-integral-derivative (PID) controller, the intermediate signal and a reference signal to generate the correction signal.
19 . The method of claim 18 , wherein the correction signal generated by the PID controller is configured to reduce a difference between the intermediate signal and the reference signal.
20 . A system comprising: a cryostat to maintain a film of liquid helium at a temperature below helium condensation temperature; a plurality of single-electron qubit structures, each of the plurality of single-electron qubit structures formed using a respective set of one or more electrodes electrostatically confining a first electron in a direction lateral to the film of liquid helium; a feedback circuitry to: subject a first single-electron qubit structure of the plurality of single-electron qubit structures to a probe signal; receive a response signal caused by an interaction of the probe signal with the first single-electron qubit structure; generate, using the response signal, a correction signal; and subject the first single-electron qubit structure and a second single-electron qubit structure of the plurality of single-electron qubit structures to the correction signal.

Description

RELATED APPLICATIONS This application claims benefit of the U.S. Provisional Patent Application No. 63/596,730 filed Nov. 7, 2023, the contents of which are incorporated in their entirety by reference herein. TECHNICAL FIELD The instant specification generally relates to systems and methods for creating qubit hardware and mechanisms for qubit control and readout for implementing quantum computing technology. BACKGROUND Quantum computing is the technology that utilizes quantum bits (qubits)—quantum systems that can be in a superposition state α|0+β|1 of two quantum states, |0 and |1, with continuously varying parameters α and β, unlike classical bits that always remain in one of the two classical states, 0 or 1. Operation of a quantum computer may include preparing multiple qubit states, achieving quantum entanglement of two or more separate qubits, causing quantum evolution of the system of entangled qubits in accord with a quantum algorithm (code) tailored to a particular task being undertaken, performing quantum readout of the end state of the entangled qubits, and—given the intrinsically probabilistic nature of quantum systems—applying suitable error-correction techniques. Quantum computers can be superior to classical computers for a number of problems (such as prime number factorization, unstructured searching, optimization, etc.) that would not be practicable on classical computers or would require exponentially large computational resources. Despite various proposed realizations of qubits and readout methods, reliable implementation of scalable quantum computing remains an outstanding technological challenge. To be feasible for actual quantum computations, qubits should have minimal coupling to extraneous objects, in order to avoid decoherence of quantum states of qubits. In particular, qubits should be able to retain their quantum coherence over times that are sufficiently long for the quantum algorithm execution and the final state readout. On the other hand, it should be possible to maintain a degree of external control over individual qubits, to prepare initial states of the qubits and to read out their final states. Successfully balancing these countervailing objectives for a large number of qubits is one or prerequisites of advanced quantum computing applications. DESCRIPTION OF DRAWINGS Aspects and implementations of the present disclosure will be understood more fully from the detailed description given below and from the accompanying drawings of various aspects and implementations of the disclosure, which, however, should not be taken to limit the disclosure to the specific aspects or implementations, but are presented for explanation and understanding purposes only. FIG. 1 illustrates schematically an example system that may serve as a reservoir of electrons for qubits and that uses liquid helium and electrostatic gates to facilitate electron confinement, according to one implementation. FIGS. 2A-2C illustrate schematically an example system that uses electrostatic gates to create electron traps and trap electrons confined near a surface of liquid helium, according to one implementation. FIG. 3 illustrates an example structure that includes a data qubit and an ancillary qubit to implement an active feedback loop that prevents environmental decoherence of the data qubit, according to one implementation. FIG. 4 is a schematic block diagram of an example active feedback system that compensates for environmental noise/fluctuations of electric potential and improves qubit coherence, according to one implementation. FIG. 5 illustrates schematically compensation of fluctuations of electrostatic potential using the active feedback system of FIG. 4, according to one implementation. FIG. 6 is a flow diagram illustrating an example method of improving qubit coherence by compensating for environmental noise/fluctuations of electric potential of qubits, according to one implementation. DETAILED DESCRIPTION Among specific realizations of qubits are qubits that are implemented via electrons trapped near a surface of liquid helium and held to the vicinity of this surface by electrostatic forces, which may include image forces of attraction to helium and/or forces caused by electric fields of gate electrodes (normally positioned below the film of helium). Additional electrostatic gates may be used to laterally confine electrons to a bounded area and further to implement electron traps outside the bounded area to capture a small number of electrons therein. The number of electrons trapped in this manner may be controlled by electrostatic gating and, in some implementations, may be equal to one. Such individual electrons may be used as qubits. The quantum states of a qubit, |0 and |1, may be realized, for example, as a ground state and an excited state of a trapped electron. In some implementations, the quantum states of the qubit may be vertical Rydberg motional states of the electron floating near the surfa