Quantum processing system

Abstract

Aspects of the present disclosure are directed to a quantum processing system including a plurality of donor atomic qubits located in a semiconductor substrate. The system also includes a plurality of control gates configured to control the donor atomic qubits. The system also includes a SLQD charge sensor fabricated on / in the semiconductor substrate. The SLQD charge sensor is configured to sense spin states of two or more donor atomic qubits located within a sensing range of the SLQD charge sensor.

Description

Technical Field

[0001] This disclosure relates to quantum processing systems, and more specifically, but not exclusively, to quantum processing systems including sensors for sensing qubits. Background Technology

[0002] The developments described in this section are known to the inventors. However, unless otherwise indicated, it should not be assumed that any developments described in this section are prior art simply because they are included in this section, or that such developments are known to a person skilled in the art.

[0003] Large-scale quantum processing systems promise a technological revolution, offering the potential to solve problems that classical machines cannot. To date, numerous different structures, materials, and architectures have been proposed for implementing quantum bits (qubits) and corresponding quantum control and processing systems. Before such large-scale quantum computers can be commercially manufactured, many obstacles need to be overcome, such as accurately measuring the state of a qubit at any given time in a quantum processing device. Different types of sensors have been proposed in this field for measuring qubit states. Some of these sensors occupy a significant portion of the quantum chip area, complicating the architectural design of quantum chips for large-scale quantum computers.

[0004] Therefore, improved quantum processing devices and systems for sensing the state of qubits are desired. Summary of the Invention

[0005] According to a first aspect, the present invention provides a quantum processing system comprising: a plurality of qubits located in a semiconductor substrate, each qubit being based on the spin state of a quantum dot embedded in the semiconductor substrate, and each quantum dot being composed of one or more donor atoms; a single-lead quantum dot (SLQD) charge sensor fabricated on / in the semiconductor substrate; and a plurality of control gates configured to control the plurality of qubits, wherein the SLQD charge sensor is configured to sense two or more qubits located within the sensing range of the SLQD charge sensor.

[0006] In this embodiment, the sensing range of the SLQD charge sensor is 300 nanometers or less.

[0007] In this embodiment, the optimal inter-qubit distance between two adjacent qubits is 5-45 nanometers.

[0008] In one embodiment, each of the plurality of control gates is located in the same plane as the plane in which the corresponding qubit and SLQD charge sensor are located.

[0009] In one embodiment, multiple qubits are arranged in a one-dimensional linear array, and an SLQD charge sensor is located near the center of the one-dimensional linear array for sensing the qubits. The SLQD charge sensor can sense four or more qubits in the one-dimensional linear array. The SLQD charge sensor can sense up to fifty qubits in the one-dimensional linear array.

[0010] In an alternative embodiment, multiple qubits are arranged in a two-dimensional arrangement, and an SLQD charge sensor is placed near the center of the two-dimensional arrangement. The SLQD charge sensor can sense up to 200 qubits in the two-dimensional arrangement.

[0011] In this embodiment, the SLQD charge sensor uses a single-shot readout process to sense the spin state of each qubit.

[0012] In this embodiment, the sensing range of the SLQD charge sensor is proportional to the capacitive coupling between the SLQD and the donor-based qubit, and this capacitive coupling is related to 1 / d 1.5 or 1 / d 1.4±0.1 It is proportional to d, where d is the distance between the SLQD charge sensor and the qubit.

[0013] In this embodiment, the SLQD charge sensor sequentially reads the spin states of two or more qubits.

[0014] In the embodiment, the donor atom is phosphorus-31 ( 31 P) Donor atom.

[0015] In an embodiment, 31 P-donor quantum dots are fabricated in silicon using atomic-precision hydrogen resist photolithography.

[0016] According to a second aspect, the present invention provides a method for manufacturing a quantum processing system, comprising the steps of: providing a plurality of qubits located in a semiconductor substrate, each qubit being based on the spin state of a quantum dot embedded in the semiconductor substrate, and each quantum dot being composed of one or more donor atoms; providing a single-lead quantum dot (SLQD) charge sensor on the semiconductor substrate; and providing a plurality of control gates configured to control the plurality of qubits, wherein the SLQD charge sensor is configured to measure two or more qubits located within the sensing range of the SLQD charge sensor. Attached Figure Description

[0017] Figure 1 This is a schematic diagram showing a linear array of multiple qubits and a single-lead quantum dot (SLQD) charge sensor for sensing the qubits;

[0018] Figure 2It is a schematic diagram of a quantum processing device including multiple qubits arranged in a two-dimensional planar structure and an SLQD charge sensor for sensing the qubits.

[0019] Figure 3 A schematic diagram of a quantum processing device is shown, comprising multiple qubits arranged in a two-dimensional ring arrangement and an SLQD charge sensor for sensing the qubits in the ring arrangement.

[0020] Figure 4 A schematic diagram of a quantum processing device is shown, comprising multiple qubits arranged in a two-dimensional octagonal configuration and an SLQD charge sensor for sensing the qubits in the octagonal configuration.

[0021] Figure 5a A schematic image of a fully epitaxial donor-based quantum processing device is shown;

[0022] Figure 5b A schematic diagram illustrating the working principle of the SLQD charge sensor is shown.

[0023] Figure 5c and Figure 5d The charge stability diagrams of the top (D1, D2) and bottom (D3, D4) pairs of the donor quantum dots are shown respectively;

[0024] Figures 6a-6e The charge sensing response of the SLQD charge sensor to the first charge transition of the quantum dot as a function of gate voltage and input power level is shown.

[0025] Figures 7a-7f The positions and experimental trajectories of the single excitation readout pulses for quantum dots D1, D2, and D3 are shown.

[0026] Figure 7g-Figure 7h A gate scan of quantum dot D4 is shown, highlighting the fast tunneling rate that prevents single-excitation readout;

[0027] Figure 8a The simulation results are shown, illustrating the expected strong response regime near the SLQD charge sensor;

[0028] Figure 8b The SLQD sensor response V is shown as a function of the distance d from the center of the SLQD sensor. M The offset curve; and

[0029] Figure 8c and Figure 8d d were highlighted respectively 1.4±0.1 Scaling and d 3The impact of scaling differences on charge sensing and readout fidelity.

[0030] This invention is subject to various modifications and alternatives, and specific embodiments are illustrated and described in detail in the accompanying drawings by way of example. However, it should be understood that the drawings and detailed descriptions are not intended to limit the invention to the specific forms disclosed. This invention is intended to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the appended claims. Detailed Implementation

[0031] Overview

[0032] The spin states of electrons or atomic nuclei in semiconductor materials are good candidates for carrying quantum information and serve as qubits (quantum bits) for quantum computing systems. Quantum computing requires three important steps: qubit initialization, qubit control, and individual qubit readout.

[0033] Spin readout is a critical requirement for fault-tolerant quantum computing in semiconductor spin qubits. Spin readout can be performed using a single-excitation spin readout, meaning the spin state can be determined using a single iteration of the readout sequence. Single-excitation readout is necessary for quantum error correction and readout at the end of the computation and must be performed with high reliability and accuracy.

[0034] The speed of measurement is a critical consideration in quantum processing systems because qubits typically maintain coherence over short time intervals (typically hundreds of microseconds). Single-excitation spin readout is typically performed by mapping the spin state of a qubit to a charge state (i.e., a spin-to-charge conversion), which can then be detected using a nearby charge sensor, such as a single-electron transistor (SET), quantum dot contact (QPC), or tunnel junction. SETs offer good sensitivity, but they are complex, occupy a large space, and require at least three electrical contacts—source, drain, and gate—that require significant geometric footprint on a quantum computing chip to operate. For the future development of complex and scalable quantum computers comprising hundreds, thousands, or millions of qubits, components with the smallest possible footprint are desired to minimize the overall footprint.

[0035] To overcome some of these issues, distributed (or gate-based) sensors are gaining popularity due to their reduction in device complexity and geometric footprint required to perform spin readout. In contrast to SETs, distributed sensors integrate qubit readout capability into existing control leads on the device chip. This eliminates the need for additional near-end charge sensors.

[0036] Recent advances have demonstrated single-excitation readout of singlet and triplet states using direct distributed sensors. One sensing strategy involves using distributed sensors to measure the magnetic susceptibility of single-electron tunneling at radio frequency, requiring only one terminal to distinguish singlet and triplet spin states on a dual quantum dot via a Pauli blockade—a technique known as “gate sensing.” One drawback of this “gate sensing” technique is that readout cannot be performed directly on a “single-spin basis.” In other words, gate sensing cannot directly read out a single electron / nucleus spin because it induces electrons to tunnel back and forth into the storage pool, disrupting the spin state before it can be resolved.

[0037] This disclosure

[0038] Different types of charge sensors, known as single-lead quantum dot (SLQD) charge sensors, can be used for electron spin readout. However, to date, SLQDs have not been used for single-excitation readout on a single-spin basis. SLQDs offer high sensitivity, require minimal wiring (i.e., a single lead, thus occupying a small space), and have a significantly smaller geometric footprint compared to SETs. Therefore, SLQD charge sensors are a good candidate for electron spin measurement in scalable electronic computing architectures.

[0039] The inventors have found that the small size of SLQDs is not a sufficient advantage for scalable quantum computers. The overall footprint of the charge sensors required to measure the spin states of qubits in scalable quantum computing chips also needs to be minimized.

[0040] SLQD charge sensors can only effectively measure the spin state of qubits located within a predefined qubit-sensor distance *d*. This qubit-sensor distance *d* depends on the capacitive charge coupling between the sensor and the charge (i.e., the charge corresponding to the spin state of the qubit). In free space, the capacitive coupling (or capacitance) between two charges is inversely proportional to the distance between the two charges (i.e., 1 / d, where d is the distance between the two charges). However, for charges located beneath a larger metallic plane, this scaling becomes 1 / d due to the formation of dipoles. 3 This is the case for accumulation-mode gate-set devices (such as undoped SiGe heterostructure devices and planar metal-oxide-semiconductor (MOS) devices), because these devices require a metal accumulation gate for their operation. In a linear array of gate-set quantum dots, capacitive coupling is 1 / d. 3The scaling factor is a function of the quantum bit-sensor distance, meaning that capacitive coupling weakens very quickly. In other words, the sensing range of SLQDs in these devices is very short, and therefore, a large number of SLQD sensors are required for devices with large-scale gate setups with multiple quanta.

[0041] Furthermore, the inventors have discovered that in atomically set donor-based qubit devices, the trapping potential for both the qubit and the sensor is naturally set by the donor potential, eliminating the need for metal-accumulated gates and resulting in extremely low gate density. Therefore, atomically set qubit devices (e.g., donor qubit devices) require less metal accumulation above and below the qubit plane. Consequently, the capacitive coupling between the SLQD charge sensor and the qubit scales as a function of the sensor-qubit distance d, and approximately follows 1 / d. 1.5 or 1 / d 1.4±0.1 Dependency. Therefore, when used in donor qubit devices with atomic settings, SLQD has a larger sensing range for measuring the spin state of qubits. This reduces the number of SLQD sensors per qubit and thus the overall sensor footprint on large-scale quantum computing devices comprising multiple qubits, providing a significant advantage for large-scale quantum computing devices where "area" is generally a very valuable resource.

[0042] Furthermore, the SLQD charge sensor requires a single lead (compared to other sensors that require multiple leads). This reduces the number of electrical contacts required on the quantum chip, thereby minimizing the sensor footprint and simplifying the geometry of potential quantum computers.

[0043] Thus, SLQD charge sensors with atomically set donor qubits offer a smaller sensor footprint achieved through two factors: a) reducing the physical size of the sensor footprint by using SLQDs instead of SETs; and b) reducing the number of SLQD sensors per qubit due to the increased sensing range of the SLQD sensors in such a device. Furthermore, donor qubit devices can be precisely fabricated / manufactured to achieve higher qubit densities, and the number of SLQD charge sensors can be more sparsely distributed among the qubits. Therefore, such a system may be suitable for realizing large-scale quantum computing devices.

[0044] Embodiments of this disclosure are directed to novel and inventive donor-based quantum computing systems that include one or more SLQD charge sensors, each SLQD charge sensor sensing multiple qubits.

[0045] Specifically, this disclosure provides a quantum processing system comprising a plurality of donor atom qubits located in a semiconductor substrate. The system also includes a plurality of control gates configured to control the donor atom qubits. The system further includes an SLQD charge sensor fabricated on / in the semiconductor substrate. The SLQD charge sensor is configured to sense the spin states of two or more donor atom qubits located within its sensing range.

[0046] For example, Figure 5a A schematic diagram of a fully epitaxial donor-based quantum processing system 50 is shown. System 50 includes four donor atom qubits D1-D4. However, the system can be designed to include tens, hundreds, thousands, or millions of dopant atom (i.e., donor or acceptor atom) qubits. In one embodiment, the dopant atom qubits can be encoded with the spin of the electron or hole associated with the dopant atom. In an example, the dopant atom qubits can be encoded with the spin of phosphorus-31 (… 31 P) The spin of the electron associated with the donor atom is used to encode the qubit. In another embodiment, it can be provided that... 31 The spin of the electron in the P-donor quantum dot encodes the qubit. 31 P-donor quantum dots were fabricated in a semiconductor substrate.

[0047] exist Figure 5a In the example shown, qubits D1-D4 are formed by confining electrons and using the spins of these electrons to carry information. R1 and R2 act as electron storage pools for qubits D1, D2 and D3, D4, respectively, and provide electrostatic regulation of the donor potential.

[0048] System 50 also includes an SLQD charge sensor 52 with leads 54. Leads 54 can be used to load electrons onto the charge sensor 52. The SLQD charge sensor 52 is provided for sensing the spin states of qubits D1-D4 within its sensing range. Specifically, the SLQD charge sensor 52 performs single-excitation spin readout via a spin-to-charge conversion technique.

[0049] System 50 also includes conductive control gates G1-G4, each of which is used to control qubits D1-D4. Although four gates are shown in this example, this may not be necessary. In other cases, fewer or more gates may be used to control qubits D1-D4.

[0050] The capacitive coupling between the charge sensor 52 and each electron in the electrons confined in the donor quantum dot is scaled as a function of the sensor-quantum distance d and can follow 1 / d. 1.5±0.1Dependency. All four qubits D1-D4 are within the sensing range of the SLQD sensor 52, and therefore, their charge states can be sensed by a single SLQD sensor 52.

[0051] The following sections describe various architectures for placing qubits and one or more SLQD charge sensors, enabling the efficient sensing of large numbers of qubits.

[0052] linear architecture

[0053] Figure 1 An exemplary qubit architecture according to aspects of this disclosure is shown. In this architecture, qubits (in the form of donor atoms) are arranged in a linear array. This example shows an array of 10 qubits Q1-Q10.

[0054] The qubits in the linear array are controlled by control gates G1-G10. An SLQD sensor 15 is placed near the center of the linear array of qubits and provides the SLQD sensor 15 to detect the spin states of qubits Q1-Q10. In this figure, for simplicity, only 10 qubits (and the corresponding 10 control gates G1-G10) are shown; however, depending on the distance between the qubits, multiple qubits (i.e., fewer or more than 10 qubits) can be located in this linear array. If the qubits are spatially arranged such that they are within the sensing range d of the SLQD sensor 15, the spin states of multiple qubits in the linear array can be read out using a single SLQD sensor 15.

[0055] Each of the multiple control gates G1-G10 lies in the same plane as the corresponding donor atom qubit and the SLQD charge sensor 15. In an embodiment, the SLQD charge sensor 15 can sense two or more qubits in a one-dimensional linear array. Alternatively, the SLQD charge sensor 15 can sense four or more qubits in a one-dimensional linear array. The number of qubits that can be sensed by the SLQD charge sensor 15 depends on the inter-qubit distance and the architecture of the quantum processing system. For example, for system architectures with inter-qubit distances in the range of 2-50 nanometers (nm), 5-45 nm is preferred, and more preferably 8-15 nm. With a sensing range of approximately 300 nm, the SLQD charge sensor can sense up to fifty qubits in a one-dimensional linear array (i.e., 25 qubits on each side of the SLQD charge sensor 15). Such a system of SLQD charge sensors can achieve very high fidelity qubit readouts of up to 99% or higher.

[0056] Gates G1-G10 are controlled by control units 11 and 12 connected via leads 13 and 14 to achieve centralized control of all gates G1-G10. For example, gates G1-G10 can be connected to a multi-channel precision voltage source controlled by a central computing / processing system.

[0057] In alternative architectures, qubits can be located in a matrix, where each row of the matrix is ​​sensed by its corresponding SLQD.

[0058] Two-dimensional unit architecture

[0059] Figures 2-4 An example of a two-dimensional cell architecture for a donor-based quantum processing device is shown. Figure 2 A two-dimensional architecture comprising three linear arrays, each containing donor atom qubits Q11-Q15, Q21-Q25, and Q31-Q35, is shown. The number of qubits shown in this two-dimensional arrangement is exemplary and can be varied. A control gate controls the donor qubits. Figure 2 The two-dimensional architecture includes control gates G11-G15, G21-G25, and G31-G35, which are provided to control an array of donor atom qubits. An SLQD charge sensor 21 is located near the center of the two-dimensional arrangement of the qubits in the three-qubit array. A single lead 22 is provided for loading electrons onto the SLQD charge sensor 21. Gates G11-G15, G21-G25, and G31-G35 are controlled by control units 23a, 23b, and 23c, respectively, which are connected to a common cell 23d via leads 24a, 24b, and 24c.

[0060] Figure 3 Another embodiment of this disclosure is shown, in which a two-dimensional ring arrangement of donor atom qubits is illustrated. Donor qubits QC1-QC10 are arranged in a ring architecture, and each of these qubits is controlled by its corresponding control gate GC1-GC10. In this ring arrangement, the number of qubits shown is exemplary, and this number can vary. An SLQD charge sensor 31 is located approximately at the center of the ring arrangement of donor qubits. A single lead 32 is provided for loading electrons onto the SLQD charge sensor 31. Gates GC1-GC10 can be configured as follows: Figures 1-2 The layout shown is controlled by a common control unit.

[0061] Figure 4Another embodiment of this disclosure is shown, illustrating a two-dimensional octagonal arrangement of donor qubits with eight equidistant arms. Each arm of the octagon includes a plurality of donor qubits. In this embodiment, the first arm includes donor qubits Q511-Q516, the second arm includes donor qubits Q521-Q526, and the third arm includes donor qubits Q531-Q536, and so on. The number of qubits shown in this two-dimensional arrangement is exemplary and can vary. The donor qubits are controlled by control gates. Figure 5 shows a plurality of control gates for this purpose. For example, the first arm includes control gates G11-G16 for controlling donor qubits Q511-Q516, and the second arm includes control gates G21-G26 for controlling donor qubits Q521-Q526, and so on. An SLQD charge sensor 41 is located approximately at the center of this arrangement for sensing the donor qubits. A single lead is provided ( Figure 4 (Not shown) is used to load electrons onto the SLQD charge sensor 41.

[0062] exist Figures 2-4 In the aforementioned two-dimensional architecture, SLQD charge sensors 21, 31, or 41 can sense two or more qubits within their sensing range. Alternatively, SLQD charge sensors 21, 31, or 41 can sense four or more qubits within their sensing range in a two-dimensional cell. In other examples, for system architectures with qubit spacing in the 5-15 nanometer (nm) range and a sensing range of approximately 300 nm in the linear direction, SLQD charge sensors can sense up to fifty qubits in each linear array of qubits (25 qubits in each direction of the linear array). This allows Figure 2 The SLQD charge sensor 21 reads out up to 150 or fewer donor qubits. Similarly, in Figure 3 In this configuration, if all donor qubits are within the sensing range of the SLQD 31, the SLQD charge sensor 31 can read out all donor qubits. Additionally, Figure 4 The SLQD charge sensor 41 in the middle can read out up to 200 or fewer donor qubits (25 qubits in each arm of the octagonal architecture).

[0063] Architecture of the prototype quantum processing device and operation of the SLQD charge sensor

[0064] As discussed above, Figure 5aA schematic image of a fully epitaxial donor-based quantum processing system 50 is shown. The system can be fabricated using atomic-precision hydrogen resist lithography on a silicon substrate using a scanning tunneling microscope (STM). During fabrication, hydrogen is selectively desorbed in the regions within the white dashed lines, setting the lithographic pattern for the device. The device is heavily doped with phosphorus within these regions, which act as metallic conductors when cooled to mK temperatures. The structure is then overgrown with an epitaxial layer of silicon and fabricated to the aluminum ohmic contacts that bury the device. The device is bonded to a printed circuit board (PCB) to transmit high-frequency signals and DC voltages, and then mounted to the cold finger of a dilution refrigerator with a base temperature of approximately 80 mK.

[0065] Sites D1, D2, D3, and D4 indicate regions with a small number of phosphorus donors. Based on STM images and electrically measured charging energies, the estimated donor number is 2 for D1, 3 for D2, 3 for D3, and 1 for D4. Conductivity control gates G1 and G2 are used for readout pulse sequences for quantum dots D1 and D2, and G3 and G4 serve the same purpose for quantum dots D3 and D4. In addition to single-shot spin readout, charge sensor 52 can also be used to determine the electron occupancy of donor sites D1–D4.

[0066] Figure 5b A schematic diagram illustrating the operation of an SLQD sensor is shown. The charge sensor 52 comprises a quantum dot tunneled to a single lead (L1). When an AC excitation is applied to L1, single-electron tunneling may occur when the Fermi level coincides with the available charge state on the quantum dot of the sensor. This causes a reflected signal Rf. outThe change in electrostatic environment can be measured using standard zero-difference techniques. This change in electrostatic environment causes a shift in the SLQD response, allowing it to operate as a charge sensor. Electron tunneling between the SLQD 52 and the single lead L1 54 becomes possible when the potential of the SLQD sensor is aligned with the Fermi level of the single lead 54. Applying an AC excitation to L1 causes an AC single-electron current to flow between the quantum dot and lead L1, which appears as an additional capacitance (quantum capacitance) in the circuit. This additional capacitance causes a change in the reflected signal by embedding the SLQD sensor in an LC resonator, which can be detected by monitoring the phase and amplitude of the signal reflected from L1. During normal operation, no DC current can flow through the SLQD. The NbTiN superconducting spiral inductor 51 can be used as a resonator, having a resonant frequency of approximately 130 MHz and a loaded quality factor of approximately 400 when coupled to L1. The AC signal is attenuated before being applied to L1, and the reflected signal is separated to the output chain using a directional coupler 52 before amplification and measurement using a standard zero-difference setting. The change in the charge environment near SLQD shifts the Coulomb peak 53 of the dispersed measurement, thus providing contrast for charge sensing.

[0067] Figure 5c The scanning voltage V is shown. L1 (Voltage at single lead L1) and V R1 A diagram illustrating the charge stability of the top pair of donor quantum dots (D1, D2) for the voltage at storage pool R1.

[0068] This illustration demonstrates the ability of the SLQD sensor 52 to characterize the charge occupation of donor quantum dots D1-D2. The periodic diagonal 55 in the illustration represents a Coulomb-like peak from the SLQD sensor 52, and donor charge transitions are observed as broken lines (56, 57) in the marked lines covering the SLQD transition lines. Insert Figure 59 shows exemplary broken lines in the SLQD transition lines with donor charge transitions. As marked, the covered dashed lines indicate D1 charge transitions, and the covered solid lines indicate D2 charge transitions. Scanning R1 to a negative voltage adds electrons to quantum dots D1 and D2. In contrast, gates G1-G4 are only capacitively coupled to the quantum dots (non-tunneling coupling), and scanning gates G1-G4 to a negative voltage typically removes electrons from the corresponding quantum dots D1-D2, respectively.

[0069] Figure 5d The scanning voltage V is shown. L1 (Voltage at single lead L1) and V R2A similar charge stability diagram of the bottom pair of donor quantum dots (D3, D4) at the voltage at reservoir R2. As marked, dashed lines indicate charge transitions in D3, and solid lines indicate charge transitions in D4. The number of electrons is distributed by completely depleting the donor electrons and then adding electrons each time a donor transition line crosses. Scanning R2 to a negative voltage adds electrons to quantum dots D3 and D4. In contrast, gates G1-G4 are only capacitively coupled to the quantum dots (non-tunneling coupling), and scanning gates G1-G4 to a negative voltage typically removes electrons from the corresponding quantum dots D3-D4, respectively.

[0070] SLQD charge sensor optimized for single-electron charge detection

[0071] To optimize the SLQD charge sensor of device 50 for time-resolved charge detection of electrons confined in donor quantum dots, the main adjustable experimental parameter is the input reflectometry power P. in In the SLQD charge sensor, the sensor signal is used as P. in The function saturates. This can be intuitively understood by considering the cyclic single-electron tunneling process that generates the dispersed signal 53. When P in When sufficiently large to completely cross the Coulomb peak, a whole electron is driven between L1 and SLQD 52 each time the reflectometer signal reverses polarity. Because there is no DC current path, the tunneling current is limited to two electrons per AC cycle. Therefore, the amplitude of the tunneling current is limited by the Coulomb blockade. The measured signal is proportional to the tunneling current in the device, and thus this is also saturated. In current measurements, P... in It is selected at the start of this signal saturation to provide optimal readout for the SLQD charge sensor.

[0072] Figures 6a-6c The gate voltage and input power P of the SLQD charge sensor are shown. in The charge sensing response of the horizontal function to the first charge transition of D1. Figure 6a P has a value below the saturation level in = -115dBm. Figure 6b Having P at the start of power saturation in = -103dBm. Figure 6c P with complete saturation in = -95dBm. Beyond the saturation point, increasing the input power does not return significantly more signal, and the Coulomb peak begins to broaden. To sense donor quantum dot electrons, P is selected at the beginning of saturation. in Value (i.e., P) in=-103dBm), which provides an optimal balance between signal contrast and coulomb peak power broadening.

[0073] Figure 6d This demonstrates the SLQD sensor response (V1) caused by electron charging events on quantum dot D1. M The offset of V. The magnitude of this offset depends on the capacitive coupling between the SLQD sensor and the target qubit. For D1, V M =7.1mV.

[0074] Furthermore, it was discovered that V is a function of the distance d between the qubit and the SLQD charge sensor 52. M The size of V is an important parameter that can be used to determine the density of SLQD charge sensors required in a quantum processing device with a given number of qubits. M An architecture that decreases slowly as a function of distance d can reduce the number of SLQD charge sensors required in a quantum processing device. Note that due to the strong capacitive coupling between the SLQD sensor and the qubit D1, for Figure 6d All P in Value, V M The width is greater than the Coulomb peak width. Therefore, in this case, the maximum signal contrast for sensing D1 is obtained by adjusting to the top of the Coulomb peak rather than the side that provides the best small signal sensitivity. This is called the strong-response charge sensing region and allows binary switching of the entire sensor signal during charge detection by the SLQD. In device 50, as... Figure 6b As shown, all four donor quantum dots D1-D4 are in state P. in In the strong response region of -103dBm, therefore P in The same value of -103dBm is used to sense all four qubits.

[0075] Figure 6e It is shown as P in The maximum sensor contrast is a function of the function, where the difference comes from the maximum sensor contrast. Figure 6a , Figure 6b and Figure 6c The values ​​are indicated by the matching shapes: star, circle, and square, respectively. For P in >-103dBm, the maximum signal saturation occurs, and exceeding this value causes power broadening, while there is no significant gain in signal height. This further demonstrates the effectiveness of using P in the following experiments. in = -103dBm is reasonable.

[0076] The maximum tunneling current that can flow at the reflectometer frequency is given by the following formula.

[0077] |I max|=|4(1-α)ef|, (1)

[0078] Where α is the lever arm between lead 54 and SLQD sensor 52, e is the electronic charge, and f is the frequency of the reflectometer signal. It should be noted that the saturation value is 4αef when the reflectometer signal is applied to the gate without tunnel coupling to the SLQD point.

[0079] For direct discrete readout, a single lead and two quantum dots are used. The differential lever arm Δα = (α1 - α2) is a scaling factor that converts the voltage applied to the lead to the energy difference generated between the first and second points (point 1 and point 2), where α1 is the lever arm between the lead and point 1, and α2 is the lever arm between the lead and point 2. For direct discrete readout, signal saturation also occurs at a value of 4Δαef. The lever arm is positive, so α > Δα always holds true for single-lead sensors, which explains why the SLQD charge sensor can have higher sensitivity than direct discrete readout.

[0080] In a typical STM device, the SLQD charge sensor is close enough to its electron storage cell (e.g., a single lead 54 for the SLQD sensor 52 in device 50) to allow tunneling to occur, so in a practical STM device, (1–α) > Δα holds (e.g., typical values ​​are (1–α) ~ 0.5, Δα ~ 0.05). In CMOS nanowire devices, α can be greater than 0.9, and Δα is approximately from 0.3 to 0.72. Therefore, the quantum capacitance (Cq ∝ α) of the SLQD charge sensor... 2 The quantum capacitance (Cq∝Δα) of a directly dispersed sensor is greater than that of a quantum capacitor. 2 The magnitude is much larger, which explains the potential for higher sensitivity in charge detection in quantum processing devices. Equation 1 also shows that increasing the reflectometer frequency generates more signal, so operating at a higher frequency can improve sensitivity.

[0081] Single-shot electron spin readout

[0082] In P in When optimized, the SLQD charge sensor (e.g., sensor 52) is ready for single-spin-based excitation of qubits (i.e., electron spin readout). In the experiment, SLQD sensor 52 was used to perform single-spin-based excitation of electron spin readouts at D1, D2, and D3. For donor point D4, the tunneling rate to R2 exceeded the measurement bandwidth, and readout could not be performed.

[0083] Figure 7 illustrates the results of this spin readout experiment using a specific set of settings. Specifically, in this experiment, a 1.5 Tesla magnetic field was applied to induce a Zeeman split in the electron spin states of D1–D3. At each donor point, a three-level pulse was executed along the SLQD transition line, where the level was... Figure 7a , Figure 7c and Figure 7e The three-level pulse is indicated by a star. Essentially, a three-level pulse consists of three constant voltage levels, and the pulse can abruptly switch to one of these three voltage levels. Specifically, the three-level pulse sequence comprises a loading phase for initializing the random electron spin state, a subsequent readout phase for projective measurement of the spin, and an empty phase for ejecting electrons before the next pulse repetition.

[0084] During the readout phase, the upper spin state tunnels into the storage pool, and then the lower spin tunnels back to the donor point, generating a characteristic "blip" signal in the charge sensor response, which is not present in the lower spin state. The pulse sequence used for this experiment can be provided by any waveform generator, where the waveform is programmed via a computing or processing device. For example, the computing or processing device could be a "central control system."

[0085] Donor quantum dots D1, D2, and D3 are sufficiently close to their respective storage pools R1 / R2 to allow electron tunneling between the dots and their respective storage pools. If energy states are available, there exists a potential barrier that electrons can overcome via quantum tunneling to move (e.g.) between D1 and R1. For spin readout, the upper spin electrons, having higher energy, will tunnel through the barrier, while the lower spin electrons will not be able to tunnel.

[0086] For readouts at the first electron transition, if the electron is up-spin during the readout phase, it will tunnel away from the donor, and the down-spin electron will tunnel back at a later time.

[0087] For D - During readout, if the electron is in an up-spin state, a down-spin electron tunnels into the storage cell to form a two-electron singlet state, and then the up-spin electron tunnels back into the storage cell. In both cases, the up-spin electron is recorded as a spike in the signal during the readout phase. If the electron is in an down-spin state, no electron tunneling occurs, and therefore no spike is observed.

[0088] Figure 7a The image shows V above a single SLQD 52 line that intersects with the first electronic charge transition of D1. G1 and V G2 The gate-to-gate diagram. Adding electrons to D1 shifts the peak position of SLQD 52 by V.M =7.1mV (where V M It's about V G1 (mutual charging voltage). Figure 7b Exemplary upper spin 71 and lower spin 72 trajectories of D1 are shown, demonstrating single-shot readout. Spin readout fidelity was calculated by taking 5000 individual single-shot trajectories and was found to be FM = 81%. Fidelity is limited by the measurement bandwidth (set to ~80 kHz in this experiment), which is insufficient to capture the fastest tunneling events. Increasing the measurement bandwidth allows for faster events, at the cost of a reduced SNR (which also reduces fidelity). In this experimental setup, 80 kHz was found to give a maximum fidelity of 81%.

[0089] Figure 7c The image shows V above a single SLQD 52 line where the scan intersects with the second electronic charge transition of D2. G1 and V G2 The gate-to-gate diagram. Due to the favorable electron tunneling rate (~2.6 kHz) at the second electron transition, D-charge readout is performed in this experiment. Figure 7d An exemplary single-excitation trajectory is shown to illustrate the difference between the up-spin (signal 73) and down-spin (signal 74) signals. Taking 5000 individual trajectories, the fidelity of D2 was found to be FM = 95%. This fidelity is again partly limited by the measurement bandwidth filtering the fastest tunneling event (which is 15 kHz in this experiment) and the relatively high electron temperature (~280 mK).

[0090] Figure 7e The image shows V above a single SLQD 52 line that intersects with the first electronic charge transition of D3. G1 and V G2 The gate-to-gate diagram. In this case, during spin readout, electrons tunnel between D3 and R2 (instead of R1 in the previous case). Figure 7f The corresponding exemplary single-excitation upper spin 75 and lower spin 76 trajectories for D3 are shown. In this case, the fidelity is calculated as F. M =95%, which is subject to the same factors as D2.

[0091] Figure 7g The gate-to-gate voltage diagram of quantum dot D4 is shown. For this donor quantum dot D4, the tunneling rate between the donor and the memory pool is too fast to perform a single-excitation spin readout. In fact, a weak signal can be observed due to the cyclic drive of electrons between D4 and R2. This means that the tunneling rate is not negligible compared to the RF reflectometer frequency (130 MHz). Figure 7h It shows Figure 7gThe magnified view of region 77 highlights the weak signal caused by donor electron tunneling. Due to the fast tunneling rate, a single-shot excitation spin readout cannot be performed on quantum dot D4.

[0092] Table I shows a summary of the single-shot readout results for the four donor points D1-D4.

[0093] Table I. Summary of single-excitation readout results for the four donor point devices.

[0094]

[0095] Remote charge sensing

[0096] This section describes the sensor offset V M An investigation of scaling as a function of the sensor-qubit distance d. First, the capacitive coupling between the SLQD sensor 52 and the qubit in device 50 was simulated using the finite element package COMSOL Multiphysics. The simulation results were plotted on... Figure 8a In the diagram, the dashed outline indicates a region where V is significantly reduced due to charging events (strong response threshold) on the target qubit. M Large enough that the SLQD 52 coulomb peak is shifted from the full signal (at the top of the peak) to <1% of the signal. The strong response region is defined as a region where >99% of the full-switching signal contrast is possible. Beyond this strong response boundary, by reducing P... in Maximum readout contrast can be achieved by biasing to the side of the coulomb peak, or both. Any qubit located within the occupied area of ​​this profile 82 will generate a full on / off switch of the sensor signal and can be measured without any loss of fidelity due to distance from the sensor.

[0097] Figure 8b The diagram shows the SLQD sensor response (V) as a function of the distance d from the center of the SLQD sensor to the device region containing the sensor and patterned qubits. M A graph showing the offset of V. Fitted to the simulated V. M Value (blue dot 83), V was found. M With d 1.4±0.1 This is directly proportional, consistent with the data from actual measurements using device 50 (shown by circle 84). Figure 8b As indicated by curve 81 in the figure, both the experimental and simulation results are related to 1 / d 3 Inconsistent scaling.

[0098] Figure 8c The effect of this scaling difference on remote charge sensing is highlighted. The left subplot uses data from... Figure 8b 1 / d 1.4 Fitting was used to estimate V at distances of 100 nm, 200 nm, and 300 nm from the SLQD sensor 52. M The solid and dashed lines show the expected positions of the SLQD Coulomb peaks at specified distances on the target qubits for 0 and 1 electrons, respectively. (This is achieved by fitting to...) Figure 6b The optimal P in in The shape of the sensor coulomb peak is determined by the line of experimental data with a value (i.e., -103 dBm). Figure 8c The arrow in the image indicates the maximum sensor contrast used to detect the electronic charge on the target. The right-hand subplot shows the use of... Figure 8b 1 / d 3 Fitting (81) to estimate V at distances of 100 nm, 200 nm, and 300 nm from the sensor M The RF response. In this case, V M The contrast decreases more rapidly with increasing distance, and is minimized at 300nm.

[0099] To highlight the importance of this scaling for scalable quantum computing, the expected single-excitation readout fidelity of the qubit as a function of d is calculated using the same parameters as point D3 in device 50. According to Figure 8b The fitting in the model estimates V as a function of d. M This is then used to calculate the expected signal contrast. Following this, the signal-to-noise ratio (SNR) is calculated using noise measured in the experiment, and then used for fidelity calculations.

[0100] Figure 8d It shows 1 / d 1.4±0.1 and 1 / d 3 The results of both. Curve 86 corresponds to 1 / d 1.4±0.1 The result shows that the shaded area 87 outlines the uncertainty limit. Curve 85 corresponds to 1 / d. 3 The results show a faster decay in readout fidelity. As observed in the direct measurements of D3, for small d, the sensor is in a strong response region with full-on-off signal contrast, and both curves saturate to 95% fidelity. It is evident from this figure that qubits with the same characteristics as D3 (i.e., donor-based qubits with low metal gate accumulation) can achieve spin readout fidelity exceeding 90% at distances up to 300 nm from the SLQD sensor, compared to 1 / d, as observed in devices with accumulation-mode gate settings. 3 Scaling at 130 nm yields spin readout fidelity exceeding 90%.

[0101] Furthermore, it was found that for a linear array of tunnel-coupled donor qubits with a typical separation distance of 12 nm between adjacent qubits, a single SQLD placed at the center of the linear array can read out up to 50 qubits, similar to D3 (i.e., donor-based qubits with low metal gate accumulation) with over 90% fidelity. This can be increased to >99% by optimizing the measurement setup to reduce the electron temperature, operating the SLQD at higher frequencies, and using a quantum-confined Josephson parametric amplifier. The equivalent number of qubits for the accumulation mode gate setting (assuming a qubit separation of 80 nm and a sensing range of 130 nm) is approximately 3. This is consistent with currently available experimental gate-setting arrays with 3-4 qubits per sensor.

[0102] In this experiment, the relaxation time T1 of D3 was measured to be 11 seconds at 1.5 Tesla. Furthermore, other experiments with donor qubits have demonstrated relaxation times as high as 30 seconds. Considering the extremely long relaxation time T1 in donor qubits and recent advances in manipulating charge states in large qubit arrays, the same SLQD charge sensor can sequentially measure 50 qubits without limiting fidelity.

[0103] The above experimental results show that, compared with obeying 1 / d 3 A comparison of previous measurements in a linear array of devices with gate-set accumulation modes based on dependency shows that, when used for donor-type qubits and single-excitation SLQD charge sensors, the capacitive coupling between the sensor and the qubit follows a 1 / d rule. 1.4±0.1 Dependency. This scaling difference has a significant impact on long-range qubit readout in future quantum processing devices where scalability is a crucial consideration. The advantageous distance scaling in the low metal gate density device 50 means that the number of sensors per qubit can be significantly reduced in future large-scale quantum processing devices. Therefore, crystal donor qubits have a dual advantage: a) qubits can be sensed from a greater distance; and b) qubits can be fabricated at a higher density due to atomic-level lithographic resolution. These results are very promising for realizing large-scale quantum computing architectures with significantly reduced sensor density at the atomic level.

[0104] The small footprint, high sensitivity, and advantageous distance sensing of SLQDs make them promising donor-based atomic qubit sensors for increasing applications in large-scale quantum processing devices.

[0105] As used in this article, the term “including” (and its grammatical variations) is used in an inclusive sense of “having” or “containing”, rather than in the sense of “consisting of only”.

[0106] Those skilled in the art will understand that many changes and / or modifications can be made to the invention as illustrated in the specific embodiments without departing from the spirit or scope of the invention as broadly described. Therefore, these embodiments should be considered illustrative in all respects, not restrictive.

Claims

1. A quantum processing system, comprising: Multiple qubits are located in a semiconductor substrate, each qubit being based on the spin state of a quantum dot embedded in the semiconductor substrate, and each quantum dot being composed of one or more donor atoms; A single-lead quantum dot (SLQD) charge sensor is fabricated in the semiconductor substrate; as well as Multiple control gates are configured to control the corresponding qubits; The SLQD charge sensor is configured to measure the spin state of two or more qubits located within the sensing range of the SLQD charge sensor.

2. The quantum processing system according to claim 1, wherein, The sensing range of the SLQD charge sensor is 300 nanometers or less.

3. The quantum processing system according to claim 1 or claim 2, wherein, The optimal qubit spacing between two adjacent qubits is 5-45 nanometers.

4. The quantum processing system according to claim 1 or claim 2, wherein, Each of the plurality of control gates is located in the same plane as the corresponding qubit and the SLQD charge sensor.

5. The quantum processing system according to claim 1 or claim 2, wherein, The plurality of qubits are arranged in a one-dimensional linear array, and the SLQD charge sensor is located near the center of the one-dimensional linear array used to sense the qubits.

6. The quantum processing system according to claim 5, wherein, The SLQD charge sensor measures the spin state of four or more qubits in the one-dimensional linear array.

7. The quantum processing system according to claim 5, wherein, The SLQD charge sensor measures the spin state of up to fifty qubits in the one-dimensional linear array.

8. The quantum processing system according to claim 1 or claim 2, wherein, The plurality of qubits are arranged in a two-dimensional arrangement, and the SLQD charge sensor is placed near the center of the two-dimensional arrangement.

9. The quantum processing system according to claim 8, wherein, The SLQD charge sensor measures the spin state of up to 200 qubits in the two-dimensional arrangement.

10. The quantum processing system according to claim 1 or claim 2, wherein, The SLQD charge sensor uses a single excitation readout process to measure the spin state of each of the qubits.

11. The quantum processing system according to claim 1 or claim 2, wherein, The sensing range of the SLQD charge sensor is proportional to the capacitive coupling between the SLQD and the donor-based qubit, and The capacitive coupling and 1 / d 1.4±0.1 It is proportional to d, where d is the distance between the SLQD charge sensor and the qubit.

12. The quantum processing system according to claim 1 or claim 2, wherein, The SLQD charge sensor sequentially reads the spin states of the two or more qubits.

13. The quantum processing system according to claim 1 or claim 2, wherein, The donor atom is phosphorus-31 ( 31 P) Donor atom.

14. The quantum processing system according to claim 13, wherein, 31 P-donor quantum dots are fabricated in silicon using atomic-precision hydrogen resist photolithography.

15. A method for manufacturing a quantum processing system, comprising the following steps: A plurality of qubits are provided in a semiconductor substrate, each qubit being based on the spin state of a quantum dot embedded in the semiconductor substrate, and each quantum dot being composed of one or more donor atoms; A single-lead quantum dot (SLQD) charge sensor is provided in the semiconductor substrate; as well as Provides a plurality of control gates configured to control the corresponding qubits; The SLQD charge sensor is configured to measure the spin state of two or more qubits located within the sensing range of the SLQD charge sensor.

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