Charge-Based Single-Shot Readout Systems in Quantum Computing

Measurement of a qubit (quantum bit) is a key element of quantum computation and is necessary for extracting information from a quantum processor. The physical implementation of a measurement protocol involves monitoring a physical quantity of a sensor, such as a current or a voltage, that is correlated with the state of the qubit to be measured. The monitoring of these sensors used to measure qubits in modern quantum computer architectures is typically divided between RF reflectometry and current/voltage monitoring. There are tradeoffs involved with both approaches for the reliable and accurate readout of qubits when it comes to scalable quantum computing architectures. In this article, we will review the working principles of a selection of sensors that are used to measure the state of qubits in semiconductors. The goal is to introduce electronic engineers with little or no background in quantum computing to the working principles of charge sensors in semiconductor quantum computers, their identification in various physical systems, and an overview of their design tradeoffs when measuring a qubit. This will allow electronic engineers to begin working with physics literature in the field of charge sensing.Measurement of a qubit (quantum bit) is a key element of quantum computation and is necessary for extracting information from a quantum processor. The physical implementation of a measurement protocol involves monitoring a physical quantity of a sensor, such as a current or a voltage, that is correlated with the state of the qubit to be measured. The monitoring of these sensors used to measure qubits in modern quantum computer architectures is typically divided between RF reflectometry and current/voltage monitoring. There are tradeoffs involved with both approaches for the reliable and accurate readout of qubits when it comes to scalable quantum computing architectures. In this article, we will review the working principles of a selection of sensors that are used to measure the state of qubits in semiconductors. The goal is to introduce electronic engineers with little or no background in quantum computing to the working principles of charge sensors in semiconductor quantum computers, their identification in various physical systems, and an overview of their design tradeoffs when measuring a qubit. This will allow electronic engineers to begin working with physics literature in the field of charge sensing.

IEEE Circuits and Systems MagazineJan 1, 20244 citations

DC-Readout of Semiconductor Spin Qubits: Opportunities and Limits

Gerd Kiene, Oriol Pietx-Casas, Masoud Babaie +2 more

This paper presents extensive guidelines for the design of an integrated DC-readout interface for semiconductor spin qubits. Since the focus is on the readout via a single electron transistor (SET), the SET behavior and performance are first described and modeled, showing that the signal-to-noise ratio (SNR) theoretically achievable by a SET-based DC-readout is significantly beyond the state-of-the-art. Practical circuit architectures for implementing a DC-readout, such as the voltage amplifier, the transimpedance amplifier, the charge sampling, and the current pre-amplifier, are then analyzed by deriving their design equations and trade-offs. As a result, the practical performances of those different solutions are evaluated and compared, thus presenting clear selection criteria for the readout architecture and its design equations given the specific parameters of the SET sensor.This paper presents extensive guidelines for the design of an integrated DC-readout interface for semiconductor spin qubits. Since the focus is on the readout via a single electron transistor (SET), the SET behavior and performance are first described and modeled, showing that the signal-to-noise ratio (SNR) theoretically achievable by a SET-based DC-readout is significantly beyond the state-of-the-art. Practical circuit architectures for implementing a DC-readout, such as the voltage amplifier, the transimpedance amplifier, the charge sampling, and the current pre-amplifier, are then analyzed by deriving their design equations and trade-offs. As a result, the practical performances of those different solutions are evaluated and compared, thus presenting clear selection criteria for the readout architecture and its design equations given the specific parameters of the SET sensor.

IEEE Transactions on Circuits and Systems I Regular PapersFeb 19, 20255 citations

Real-Time Feedback Control of Charge Sensing for Quantum Dot Qubits

Takashi Nakajima, Yohei Kojima, Yoshihiro Uehara +4 more

Measuring electrical charge with single-electron resolution is essential for implementing spin qubits in semiconductor quantum dots. Applying quantum dot charge sensors in larger-scale quantum computing devices is being held back because these sensors are easily affected by environmental disturbances, and thus require elaborate tune-up. This study uses a feedback control circuit implemented on a field-programmable gate array to maintain sensor performance in the face of capacitive crosstalk and charge noise. The technique enables rapid tune-up of quantum dot devices and reliable single-shot electron or spin measurement, and will advance the development of large-scale spin-qubit devices.Measuring electrical charge with single-electron resolution is essential for implementing spin qubits in semiconductor quantum dots. Applying quantum dot charge sensors in larger-scale quantum computing devices is being held back because these sensors are easily affected by environmental disturbances, and thus require elaborate tune-up. This study uses a feedback control circuit implemented on a field-programmable gate array to maintain sensor performance in the face of capacitive crosstalk and charge noise. The technique enables rapid tune-up of quantum dot devices and reliable single-shot electron or spin measurement, and will advance the development of large-scale spin-qubit devices.

arXiv:2103.15258Physical Review AppliedMar 26, 202126 citations

Radio-Frequency Capacitive Gate-Based Sensing

Imtiaz Ahmed, J. A. Haigh, Simon Schaal +8 more

Quantum computation requires a qubit-specific measurement capability to read out the final states of individual qubits. Promising semiconductor architectures use external readout electrometers, but these could be replaced by more scalable $g\phantom{\rule{0}{0ex}}a\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}e$ $s\phantom{\rule{0}{0ex}}e\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}s\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}r\phantom{\rule{0}{0ex}}s$, based on the dispersive coupling between an electrical resonator and the qubit. The authors present an optimized gate sensor and show that significantly better sensitivity arises from changing circuit topology to enhance the resonator's $Q$ factor. Here CMOS-based quantum devices achieve charge sensitivity on par with that of the best single-electron electrometers.Quantum computation requires a qubit-specific measurement capability to read out the final states of individual qubits. Promising semiconductor architectures use external readout electrometers, but these could be replaced by more scalable $g\phantom{\rule{0}{0ex}}a\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}e$ $s\phantom{\rule{0}{0ex}}e\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}s\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}r\phantom{\rule{0}{0ex}}s$, based on the dispersive coupling between an electrical resonator and the qubit. The authors present an optimized gate sensor and show that significantly better sensitivity arises from changing circuit topology to enhance the resonator's $Q$ factor. Here CMOS-based quantum devices achieve charge sensitivity on par with that of the best single-electron electrometers.

arXiv:1801.09759Physical Review AppliedJul 19, 201875 citations

Benchmarking high fidelity single-shot readout of semiconductor qubits

Daniel Keith, Samuel Keith Gorman, Ludwik Kranz +4 more

Abstract Determination of qubit initialisation and measurement fidelity is important for the overall performance of a quantum computer. However, the method by which it is calculated in semiconductor qubits varies between experiments. In this paper we present a full theoretical analysis of electronic single-shot readout and describe critical parameters to achieve high fidelity readout. In particular, we derive a model for energy selective state readout based on a charge detector response and examine how to optimise the fidelity by choosing correct experimental parameters. Although we focus on single electron spin readout, the theory presented can be applied to other electronic readout techniques in semiconductors that use a reservoir.Abstract Determination of qubit initialisation and measurement fidelity is important for the overall performance of a quantum computer. However, the method by which it is calculated in semiconductor qubits varies between experiments. In this paper we present a full theoretical analysis of electronic single-shot readout and describe critical parameters to achieve high fidelity readout. In particular, we derive a model for energy selective state readout based on a charge detector response and examine how to optimise the fidelity by choosing correct experimental parameters. Although we focus on single electron spin readout, the theory presented can be applied to other electronic readout techniques in semiconductors that use a reservoir.

arXiv:1811.03630New Journal of PhysicsMay 23, 201948 citations

Fast Readout in Semiconductor Quantum Dots

Wilson, Tim J

The need for fast readout to measure the state of a quantum dot device has important applications in the capabilities of using them as a means for quantum information processing. Traditional charge sensors used to readout the charge state of a quantum dot device are very robust and sensitive electrometers that have been in use since the late 1980s. They pose an issue to the future of quantum dots as a viable means of quantum computing, and that is in their slow acquisition times of the charge state of the quantum dot. This rate of measurement means that implementing any quantum error correction scheme becomes very difficult or even unfeasible as the coherence times of these semiconductor systems is short compared to charge sensor’s acquisition times. A possibility to speed up the measurement process of the charge state is possible thanks to the atomic molecular and optical (AMO) physics community.Cavity quantum electrodynamics (CQED) is the study of light-matter interactions when both the light and matter are taken to be quantized. A photon may interact with an atom via a dipole interaction to excite it from its ground state to its excited state, and the reverse can occur where the atom emits a photon and decays from its excited state ii to the ground state. This fundamental interaction which has been extensively studied in the AMO community since the early 1960s had been adopted by the superconducting qubit community to measure the state of their qubits. These superconducting qubits, representing atoms, which are coupled to a resonant structure on chip, which represents the photons that can interact with the artificial atom. Since these systems were not traditional trapped or neutral atoms interacting with a photon via a laser, but instead planar circuit structures, the superconducting qubit community re-coined the term cavity quantum electrodynamics to circuit quantum electrodynamics, which we will refer to as cQED.The quantum dot community adapted these methods of what is known as dispersive readout; a capacitive change of the atomic like system, results in a dispersive shift which then alters the characteristic frequency response of the resonant structure. This has allowed for a new kind of charge sensor by means of measuring the resonators response due to its coupling to a quantum dot system. This can be done with very high frequency microwave circuitry, allowing much faster readout than is capable via traditional charge sensors. Thus, allowing a pathway to implement quantum error correction schemes with reasonable times compared to any dephasing or decoherence times of the semiconductor system. Furthermore, such fast readout allows for feedback protocols to be implemented to the system to correct for certain undesirable effects due to instruments or the system itself. Our work focuses on a limit of this cQED interaction of the quantum dots to a resonant structure allowing us to do fast readout of the quantum dot charge states via a dispersive shift.The work I will demonstrate in this dissertation will be in the efforts of fast readout on the charge occupation of a double quantum dot system which is galvanically coupled to a superconducting microwave resonator. This was done in a Si/SiGe heterostructure system where I designed, simulated, and fabricated the device which was optimized to have a stronger dispersive shift signal due to an enhanced gate lever arm that couples to the resonator. I will discuss our results of attaining a minimum integration time of 34.54 ns for a unity signal to noise ratio. This demonstrates a fast readout system in the community iii which could be extended to allow for even better readout speeds with faster instruments than what were available to me for the experiment. I will further discuss our characterization of the hybrid system and how we extracted a charge noise due to charging events between the two dots in our system up to around 10 kHz. This work demonstrates a robust dispersive readout scheme which helps in the scalability of hybrid superconducting-semiconducting architectures for means of quantum information processing.The need for fast readout to measure the state of a quantum dot device has important applications in the capabilities of using them as a means for quantum information processing. Traditional charge sensors used to readout the charge state of a quantum dot device are very robust and sensitive electrometers that have been in use since the late 1980s. They pose an issue to the future of quantum dots as a viable means of quantum computing, and that is in their slow acquisition times of the charge state of the quantum dot. This rate of measurement means that implementing any quantum error correction scheme becomes very difficult or even unfeasible as the coherence times of these semiconductor systems is short compared to charge sensor’s acquisition times. A possibility to speed up the measurement process of the charge state is possible thanks to the atomic molecular and optical (AMO) physics community.Cavity quantum electrodynamics (CQED) is the study of light-matter interactions when both the light and matter are taken to be quantized. A photon may interact with an atom via a dipole interaction to excite it from its ground state to its excited state, and the reverse can occur where the atom emits a photon and decays from its excited state ii to the ground state. This fundamental interaction which has been extensively studied in the AMO community since the early 1960s had been adopted by the superconducting qubit community to measure the state of their qubits. These superconducting qubits, representing atoms, which are coupled to a resonant structure on chip, which represents the photons that can interact with the artificial atom. Since these systems were not traditional trapped or neutral atoms interacting with a photon via a laser, but instead planar circuit structures, the superconducting qubit community re-coined the term cavity quantum electrodynamics to circuit quantum electrodynamics, which we will refer to as cQED.The quantum dot community adapted these methods of what is known as dispersive readout; a capacitive change of the atomic like system, results in a dispersive shift which then alters the characteristic frequency response of the resonant structure. This has allowed for a new kind of charge sensor by means of measuring the resonators response due to its coupling to a quantum dot system. This can be done with very high frequency microwave circuitry, allowing much faster readout than is capable via traditional charge sensors. Thus, allowing a pathway to implement quantum error correction schemes with reasonable times compared to any dephasing or decoherence times of the semiconductor system. Furthermore, such fast readout allows for feedback protocols to be implemented to the system to correct for certain undesirable effects due to instruments or the system itself. Our work focuses on a limit of this cQED interaction of the quantum dots to a resonant structure allowing us to do fast readout of the quantum dot charge states via a dispersive shift.The work I will demonstrate in this dissertation will be in the efforts of fast readout on the charge occupation of a double quantum dot system which is galvanically coupled to a superconducting microwave resonator. This was done in a Si/SiGe heterostructure system where I designed, simulated, and fabricated the device which was optimized to have a stronger dispersive shift signal due to an enhanced gate lever arm that couples to the resonator. I will discuss our results of attaining a minimum integration time of 34.54 ns for a unity signal to noise ratio. This demonstrates a fast readout system in the community iii which could be extended to allow for even better readout speeds with faster instruments than what were available to me for the experiment. I will further discuss our characterization of the hybrid system and how we extracted a charge noise due to charging events between the two dots in our system up to around 10 kHz. This work demonstrates a robust dispersive readout scheme which helps in the scalability of hybrid superconducting-semiconducting architectures for means of quantum information processing.

Dec 12, 20250 citations

Q

factor. Here CMOS-based quantum devices achieve charge sensitivity on par with that of the best single-electron electrometers.