Quantum processing system

Abstract

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

Description

【Technical Field】 【0001】 Aspects of the present disclosure relate to, but are not limited to, quantum processing systems, particularly quantum processing systems that include sensors for detecting qubits. 【Background Art】 【0002】 The developments described in this section are known to the inventors. However, unless otherwise indicated, none of the developments described in this section shall be deemed to be prior art merely by virtue of their inclusion in this section, or known to one of ordinary skill in the art having normal skill. 【0003】 Large-scale quantum processing systems hold the potential for a technological revolution and may be able to solve problems that are beyond the reach of classical machines. To date, several different structures, materials, and architectures have been proposed for implementing quantum bits (or qubits) and corresponding quantum control and processing systems. Before such large-scale quantum computers can be commercially manufactured, several hurdles need to be overcome, such as the accurate measurement of qubit states at any given point in time in a quantum processing device. Various types of sensors for measuring qubit states have been proposed in the art. Some of these sensors occupy a large portion of the area of a quantum chip, thereby complicating the architecture design of the quantum chip of a large-scale quantum computer. 【0004】 Therefore, improved quantum processing devices and systems for detecting qubit states are desirable. 【Summary of the Invention】 【Means for Solving the Problems】 【0005】 According to a first aspect, the present invention provides a quantum processing system including a plurality of qubits disposed in a semiconductor substrate, each qubit being based on the spin state of a quantum dot embedded in the semiconductor substrate, each quantum dot consisting of one or more donor atoms, a single lead quantum dot (SLQD) charge sensor fabricated on / within the semiconductor substrate, and a plurality of control gates configured to control the plurality of qubits, wherein the SLQD charge sensor is configured to detect two or more qubits disposed within the detection range of the SLQD charge sensor. 【0006】 In one embodiment, the detection range of the SLQD charge sensor is 300 nanometers or less. 【0007】 In one embodiment, the optimal inter-qubit distance between two adjacent qubits is 5 to 45 nanometers. 【0008】 In one embodiment, each of the plurality of control gates is disposed in the same plane as the plane in which the corresponding qubit and the SLQD charge sensor are disposed. 【0009】 In one embodiment, the plurality of qubits are arranged in a one-dimensional linear array, and the SLQD charge sensor is disposed near the center of the one-dimensional linear array for detecting the qubits. The SLQD charge sensor can detect four or more qubits within the one-dimensional linear array. The SLQD charge sensor can detect a maximum of 50 qubits within the one-dimensional linear array. 【0010】 In an alternative embodiment, the plurality of qubits are arranged in a two-dimensional array, and the SLQD charge sensor is placed near the center of the two-dimensional array. The SLQD charge sensor can detect a maximum of 200 qubits within the two-dimensional array. 【0011】 In one embodiment, the SLQD charge sensor detects the spin state of each qubit using a single-shot readout process. 【0012】 In one embodiment, the detection range of the SLQD charge sensor is directly proportional to the electrostatic coupling between the SLQD and the donor base qubit, where the electrostatic coupling is 1 / d 1.5 or 1 / d 1.4±0.1 It is directly proportional to , where d is the distance between the SLQD charge sensor and the qubit. 【0013】 In one embodiment, the SLQD charge sensor sequentially reads the spin states of two or more qubits. 【0014】 In one embodiment, the donor atom is phosphorus 31( 31 P) is a donor atom. 【0015】 In one embodiment, 31 P donor quantum dots are fabricated in silicon using atomic-precision hydrogen registry scopy. 【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 arranged 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 consisting of one or more donor atoms; providing a single-read 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 arranged within the detection range of the SLQD charge sensor. [Brief explanation of the drawing] 【0017】 [Figure 1] This is a schematic diagram showing a linear array of multiple qubits and a single-read quantum dot (SLQD) charge sensor for detecting the qubits. [Figure 2]This is a schematic diagram of a quantum processing device that includes multiple qubits arranged in a two-dimensional planar array and an SLQD charge sensor for detecting the qubits. [Figure 3] A schematic diagram of a quantum processing device is shown, which includes multiple qubits arranged in a two-dimensional ring-shaped array and an SLQD charge sensor for detecting the qubits within the ring-shaped array. [Figure 4] A schematic diagram of a quantum processing device is shown, which includes multiple qubits arranged in a two-dimensional octagonal array and an SLQD charge sensor for detecting the qubits within the octagonal array. [Figure 5(a)] A schematic diagram of an all-epitaxial donor-based quantum processing device is shown. [Figure 5(b)] A schematic diagram illustrating the operating principle of the SLQD charge sensor is shown. [Figure 5(c)] The charge stability diagram for the upper (D1, D2) pair of donor quantum dots is shown. [Figure 5(d)] The charge stability diagram for the lower (D3, D4) pair of donor quantum dots is shown. [Figure 6(a)] The charge detection response of the SLQD charge sensor for the first charge transition of the quantum dot is shown as a function of gate voltage and input power level. [Figure 6(b)] The charge detection response of the SLQD charge sensor for the first charge transition of the quantum dot is shown as a function of gate voltage and input power level. [Figure 6(c)] The charge detection response of the SLQD charge sensor for the first charge transition of the quantum dot is shown as a function of gate voltage and input power level. [Figure 6(d)] The charge detection response of the SLQD charge sensor for the first charge transition of the quantum dot is shown as a function of gate voltage and input power level. [Figure 6(e)] The charge detection response of the SLQD charge sensor for the first charge transition of the quantum dot is shown as a function of gate voltage and input power level. [Figure 7(a)]This shows the pulse position of the single-shot readout from quantum dot D1. [Figure 7(b)] This shows an experimental trace of a single-shot readout of quantum dot D1. [Figure 7(c)] This shows the pulse position of the single-shot readout from quantum dot D2. [Figure 7(d)] This shows an experimental trace of a single-shot readout from quantum dot D2. [Figure 7(e)] This shows the pulse position of the single-shot readout from quantum dot D3. [Figure 7(f)] This shows an experimental trace of a single-shot readout from quantum dot D3. [Figure 7(g)] This shows a gate scan of a quantum dot D4, highlighting the fast tunneling rate that prevented single-shot readouts. [Figure 7(h)] This shows a gate scan of a quantum dot D4, highlighting the fast tunneling rate that prevented single-shot readouts. [Figure 8(a)] The simulation results show the expected strong response region near the SLQD charge sensor. [Figure 8(b)] This shows a plot of the shift VM of the SLQD sensor response as a function of distance d from the center of the SLQD sensor. [Figure 8(c)] This highlights the impact of the difference between d1.4±0.1 scaling and d3 scaling for charge detection. [Figure 8(d)] This highlights the impact of the difference between d1.4±0.1 scaling and d3 scaling on read fidelity. 【0018】 While the present invention is suitable for various modifications and alternative forms, specific embodiments are shown as examples in the drawings and described in detail. However, it should be understood that the drawings and detailed description are not intended to limit the invention to any specific form disclosed. The intention is to cover all modifications, equivalents, and alternatives that fall within the spirit and scope of the invention as defined by the appended claims. [Modes for carrying out the invention] 【0019】 Overview The spin states of electrons or atomic nuclei in semiconductor materials are excellent candidates for carrying quantum information and acting as qubits (or quantum bits) in quantum computing systems. Quantum computing requires three key steps: qubit initialization, qubit control, and the readout of individual qubits. 【0020】 Spin readout is a critical requirement for fault-tolerant quantum computing in semiconductor spin qubits. Spin readout can be performed using single-shot spin readout, meaning the spin state can be determined in a single iteration of the readout sequence. Single-shot readout is necessary for quantum error correction and the final readout of the computation, and must be performed with high reliability and precision. 【0021】 Since qubits typically maintain coherence for short periods (usually hundreds of microseconds), measurement speed is a critical consideration in quantum processing systems. Single-shot spin readouts are typically performed by mapping the qubit's spin state to a charge state (i.e., spin-charge conversion), which can then be detected using a single-electron transistor (SET), quantum point contact (QPC), or a very close charge sensor such as a tunnel junction. While SETs offer good sensitivity, they are complex, occupy a large space, and require at least three electrical contacts—source, drain, and gate—to operate, resulting in a considerable geometric footprint on the quantum computing chip. To minimize this for the future development of complex and scalable quantum computers containing hundreds, thousands, or millions of qubits, components with the smallest possible footprint are desirable. 【0022】 To overcome some of these problems, distributed (or gate-based) sensors are gaining popularity because they reduce the complexity and geometric footprint of the devices required for spin readout. In contrast to SETs, distributed sensors integrate qubit readout capabilities into existing control leads on the device chip, eliminating the need for additional proximity charge sensors. 【0023】 Recent advances have demonstrated single-shot readouts of singlet and triplet states using direct dispersion sensors. One detection strategy involves using a dispersion sensor to measure the sensitivity of single-electron tunneling at radio frequencies, which requires only one terminal to distinguish between singlet and triplet spin states on a double quantum dot using a Pauli blocade, so-called "gate sensing." One drawback of this "gate sensing" technique is that it cannot perform direct readouts on a "single-spin basis." In other words, gate sensing techniques cannot directly read single electron / nuclear spins because they tunnel electrons back and forth into a reservoir and destroy the spin state before it can be resolved. 【0024】 This disclosure A different type of charge sensor, known as a single-read quantum dot (SLQD) charge sensor, can be used for electron spin readout. However, SLQDs have not been used for single-shot readout on a single-spin basis until now. SLQDs have high sensitivity, require minimal wiring (i.e., single-read, and therefore occupy less space), and have a significantly smaller geometric footprint compared to SETs. Therefore, SLQD charge sensors are good candidates for electron spin measurement in scalable quantum computing architectures. 【0025】 The inventors have found that the small size of SLQDs is not a sufficient advantage for scalable quantum computers. The overall footprint of charge sensors required to measure the spin state of qubits in a scalable quantum computing chip also needs to be minimized. 【0026】 SLQD charge sensors can effectively measure only the spin state of qubits within a given qubit-sensor distance d. This qubit-sensor distance d depends on the electrostatic charge coupling between the sensor and the charge (i.e., the charge corresponding to the qubit's spin state). In free space, the electrostatic 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, this scaling is due to the formation of dipoles in charges located beneath a large metal surface, resulting in 1 / d. 3 This is true for storage mode gate-defined devices such as undoped SiGe heterostructure devices and planar metal-oxide-semiconductor (MOS) devices, as these devices require a metal storage gate for operation. In a linear array of gate-defined quantum dots, the electrostatic coupling is 1 / d 3 The electrostatic coupling fluctuates as a function of the qubit-sensor distance, meaning it weakens very rapidly as a function of the qubit-sensor distance. In other words, the detection range of SLQDs in these devices is very short, and therefore large gate-defined devices with multiple qubits require a large number of SLQD sensors. 【0027】 Furthermore, the inventors have found that in atomically defined donor-based qubit devices, the donor potential naturally defines the trap potentials of both the qubit and the sensor, eliminating the need for a metal storage gate and resulting in an extremely low gate density. Therefore, atomically defined qubit devices, such as donor qubit devices, require less metal storage above and below the qubit plane. Consequently, the electrostatic coupling between the SLQD charge sensor and the qubit fluctuates up and down as a function of the sensor-qubit distance d, and is 1 / d 1.5 or 1 / d 1.4±0.1 It roughly follows the dependency. Therefore, SLQD has a larger detection range for measuring the spin state of a qubit when used in an atomically defined donor qubit device. This reduces the number of SLQD sensors per qubit, and consequently the overall sensor footprint on large quantum computing devices containing multiple qubits, providing a significant advantage for large quantum computing devices where "space" is generally a very valuable resource. 【0028】 Furthermore, SLQD charge sensors require only 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 geometric layout of a potential quantum computer. 【0029】 In this way, the SLQD charge sensor based on atomically defined donor qubits provides a small sensor footprint achieved through both a) a reduction in the physical size of the sensor footprint by replacing the SET with an SLQD, and b) a reduction in the number of SLQD sensors per qubit due to an increase in the detection range of the SLQD sensor in such devices. Further, the donor qubit device can be fabricated / designed precisely to have a higher qubit density, and the number of SLQD charge sensors can be placed more sparsely among the qubits. Thus, such a system may be suitable for realizing large-scale quantum computing devices. 【0030】 Embodiments of the present disclosure are directed to a novel and inventive donor-based quantum computing system that includes one or more SLQD charge sensors each detecting a plurality of qubits. 【0031】 In particular, the present disclosure provides a quantum processing system that includes a plurality of donor atom qubits disposed within a semiconductor substrate. The system also includes a plurality of control gates. The plurality of control gates are configured to control the donor atom qubits. The system further includes an SLQD charge sensor fabricated on / within the semiconductor substrate. The SLQD charge sensor is configured to detect the spin states of two or more donor atom qubits disposed within the detection range of the SLQD charge sensor. 【0032】 For example, FIG. 5(a) shows a schematic diagram of an all-epitaxial donor-based quantum processing system 50. The system 50 includes four donor atom qubits D1 to D4. However, the system can be designed to include dozens, hundreds, thousands, or millions of dopant atom (i.e., donor atom or acceptor atom) qubits. In one embodiment, the dopant atom qubits can be encoded in the spin of an electron or hole associated with the dopant atom. In one example, phosphorus 31 ( 31P) Qubits can be encoded in the electron spin associated with a donor atom. In another embodiment, the qubits are fabricated within a semiconductor substrate. 31 The spin of the electrons provided within the P donor quantum dot can be encoded. 【0033】 In the example shown in Figure 5(a), qubits D1 to D4 are formed by confining electrons and using the spin of these electrons to carry information. R1 and R2 act as electron reservoirs for qubits D1, D2 and D3, D4, respectively, and also provide electrostatic tuning of the donor potential. 【0034】 System 50 also includes an SLQD charge sensor 52 having leads 54. The leads 54 can be used to load electrons into the charge sensor 52. The SLQD charge sensor 52 is provided to detect the spin states of qubits D1 to D4 located within its detection range. In particular, the SLQD charge sensor 52 performs single-shot spin readout via spin-to-charge conversion technology. 【0035】 System 50 further includes conduction control gates G1-G4, each of which controls qubits D1-D4. While 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. 【0036】 The electrostatic coupling between the charge sensor 52 and each electron confined in the donor quantum dot fluctuates up and down as a function of the sensor-qubit distance d, and 1 / d 1.5±0.1 It depends on the dependency. All four qubits D1 to D4 are within the detection range of the SLQD sensor 52, and therefore these charge states can be detected by a single SLQD sensor 52. 【0037】 The following sections describe various architectures for arranging qubits and one or more SLQD charge sensors so that a large number of qubits can be efficiently detected. 【0038】 Linear architecture Figure 1 shows an example of a qubit architecture according to an aspect of the present disclosure. 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 to Q10. 【0039】 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 is provided to detect the spin states of qubits Q1-Q10. In this figure, only 10 qubits (and corresponding 10 control gates G1-G10) are shown for simplification, but multiple qubits (i.e., fewer than 10 or more than 10 qubits) may be arranged in this linear array depending on the distance between qubits. The spin states of multiple qubits in the linear array can be read out using a single SLQD sensor 15 if the qubits are spatially arranged so that they are within the detection range d of the SLQD sensor 15. 【0040】 Each of the control gates G1 to G10 is positioned in the same plane as the corresponding donor atom qubits and the SLQD charge sensor 15. In one embodiment, the SLQD charge sensor 15 may detect two or more qubits in a one-dimensional linear array. Alternatively, the SLQD charge sensor 15 may detect four or more qubits in a one-dimensional linear array. The number of qubits that can be detected by the SLQD charge sensor 15 depends on the qubit-to-qubit distance and the architecture of the quantum processing system. For example, in a system architecture where the qubit-to-qubit distance is in the range of 2 to 50 nanometers (nm), preferably 5 to 45 nm, more preferably 8 to 15 nm, the detection range is approximately 300 nm, and the SLQD charge sensor may detect up to 50 qubits in a one-dimensional linear array (i.e., 25 qubits on each side of the SLQD charge sensor 15). The SLQD charge sensor in such a system can achieve very high fidelity qubit readout of up to 99% or more. 【0041】 Gates G1 to G10 are controlled by control units 11 and 12, which may be connected via leads 13 and 14 to achieve central control of all gates G1 to G10. For example, gates G1 to G10 may be connected to a multi-channel precision voltage source controlled by a central computing / processing system. 【0042】 In the alternative architecture, qubits are arranged in a matrix, and each row of the matrix is ​​found by its corresponding SLQD. 【0043】 2D Unit Cell Architecture Figures 2–4 show examples of two-dimensional unit cell architectures for donor-based quantum processing devices. Figure 2 shows a two-dimensional architecture including three linear arrays containing donor atom qubits Q11–Q15, Q21–Q25, and Q31–Q35, respectively. In this two-dimensional array, the number of qubits shown is illustrative and may vary. Control gates control the donor qubits. The two-dimensional architecture in Figure 2 includes control gates G11–G15, G21–G25, and G31–G35 provided to control the array of donor atom qubits. An SLQD charge sensor 21 is located near the center of the two-dimensional array of qubits in these three qubit arrays. A single read 22 is provided to load electrons into 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 the common unit 23d via leads 24a, 24b, and 24c. 【0044】 Figure 3 shows a further embodiment of the present disclosure, in which a two-dimensional ring-shaped arrangement of donor atom qubits is shown. The donor qubits QC1-QC10 are arranged in a ring-shaped architecture, and each of these qubits is controlled by its corresponding control gates GC1-GC10. In this ring-shaped arrangement, the number of qubits shown is illustrative and may vary. An SLQD charge sensor 31 is positioned approximately in the center of the ring-shaped arrangement of donor qubits. A single lead 32 is provided for loading electrons into the SLQD charge sensor 31. The gates GC1-GC10 may be controlled by a common control unit, as discussed in the arrangements shown in Figures 1-2. 【0045】 Figure 4 shows a further embodiment of the present disclosure, which includes a two-dimensional octagonal array having eight equidistant arms of donor qubits. Each arm of the octagon contains a plurality of donor qubits. In this embodiment, the first arm contains donor qubits Q511-Q516, the second arm contains donor qubits Q521-Q526, the third arm contains donor qubits Q531-Q536, and so on. In this two-dimensional array, the number of qubits shown is illustrative and may 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 contains control gates G11-G16 for controlling donor qubits Q511-Q516, the second arm contains control gates G21-G26 for controlling donor qubits Q521-Q526, and so on. An SLQD charge sensor 41 is positioned approximately in the center of this array to detect the donor qubits. A single lead (not shown in Figure 4) is provided for loading electrons into the SLQD charge sensor 41. 【0046】 In the two-dimensional architectures shown in Figures 2-4 above, the SLQD charge sensors 21, 31, or 41 can detect two or more qubits located within their detection range. Alternatively, the SLQD charge sensors 21, 31, or 41 can detect four or more qubits located within their detection range in the two-dimensional unit cell. In a further example, in a system architecture where the qubit-to-qubit distance is in the range of 5-15 nanometers (nm) and the detection range is approximately 300 nm in the linear direction, the SLQD charge sensor can detect up to 50 qubits in each linear array of qubits (25 qubits in each direction of the linear array). This allows the SLQD charge sensor 21 in Figure 2 to read out up to 150 donor qubits. Similarly, in Figure 3, the SLQD charge sensor 31 can read out all donor qubits if all donor qubits are located within the detection range of the SLQD 31. Furthermore, the SLQD charge sensor 41 in Figure 4 can read out up to 200 donor qubits (25 qubits in each arm of the octagonal architecture). 【0047】 Architecture of a prototype quantum processing device and operation of an SLQD charge sensor As described above, Figure 5a shows a schematic diagram of an all-epitaxial donor-based quantum processing system 50. This system can be fabricated by performing atomic-precision hydrogen lithography on a silicon substrate using a scanning tunneling microscope (STM). During fabrication, hydrogen is selectively desorbed from the region inside the white dotted line to define the lithographic pattern of the device. Phosphorus is highly doped within these regions of the device, which acts as a metallic conductor when cooled to an mK temperature. Then, an epitaxial layer of silicon is grown on the structure to create aluminum ohmic contacts to the embedded device. The device is coupled to a printed circuit board (PCB) to deliver high-frequency signals and DC voltages, and then the device is mounted on the cold finger of a dilution refrigerator at a base temperature of approximately 80 mK. 【0048】 Regions D1, D2, D3, and D4 indicate areas where a small number of Lindners have been incorporated. Based on STM imaging and electrically measured charge energies, the number of donors is estimated to be 2 in D1, 3 in D2, 3 in D3, and 1 in D4. Conduction 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 may also be used to determine electron occupation of donor dots D1-D4. 【0049】 A schematic diagram of the operating principle of the SLQD sensor is shown in Figure 5(b). The charge sensor 52 includes a quantum dot tunnel-coupled to a single lead (L1). When AC excitation is applied to L1, single-electron tunneling can occur when the Fermi energy matches the available charge state on the sensor's quantum dot. This allows for the measurement of a reflected signal Rf, which can be measured using standard homodyne techniques. outA change is triggered. The change in the electrostatic environment shifts the SLQD response, enabling it to operate as a charge sensor. When the potential of the SLQD sensor is matched with the Fermi energy of the single lead 54, electron tunneling between the SLQD 52 and the single lead L1 54 becomes possible. Applying AC excitation to L1 causes an AC single-electron current to flow between the quantum dot and lead L1, which appears as an extra capacitance (quantum capacitance) in the circuit. By embedding the SLQD sensor in an LC resonator, this extra capacitance causes a change in the reflected signal that can be detected by monitoring the phase and amplitude of the signal reflected from L1. During normal operation, DC current cannot flow through the SLQD. An NbTiN superconducting spiral inductor 51 with a resonant frequency of approximately 130 MHz and a load quality factor of approximately 400 when coupled to L1 can be used as the resonator. The AC signal is first attenuated before being applied to L1, and the reflected signal is separated to the output chain using a directional coupler 52, after which amplification and measurement are performed using a standard homodyne setup. Changes in the charge environment near the SLQD cause a shift in the dispersively measured Coulomb peak 53, providing contrast for charge detection. 【0050】 Figure 5(c) shows the sweep voltage V L1 (Voltage of single lead L1) and V R1 The charge stability diagram of the upper pair (D1, D2) of donor quantum dots at (voltage of reservoir R1) is shown. 【0051】 This diagram illustrates the ability of the SLQD sensor 52 to characterize the charge occupation of donor quantum dots D1-D2. The periodic diagonal lines 55 in the diagram are Coulomb-like peaks from the SLQD sensor 52, and the donor charge transitions are observed as breaks in the labeled lines (56, 57) where they overlap the SLQD transition lines. Inset 59 shows an example of a break in the SLQD transition line due to a donor charge transition. As labeled, the superimposed dotted line represents the charge transition of D1, and the superimposed solid line represents the charge transition of D2. By sweeping R1 to a negative voltage, electrons are added to quantum dots D1 and D2. In contrast, gates G1-G4 are only electrostatically coupled to the quantum dots (not tunnel coupled), and by sweeping gates G1-G4 to a negative voltage, electrons are typically removed from the corresponding quantum dots D1-D2, respectively. 【0052】 Figure 5d shows V L1 (Voltage of single lead L1) and V R2 A similar charge stability diagram for the lower pair of donor quantum dots (D3, D4) is shown, with the (voltage across reservoir R2) swept. As indicated, the dotted line represents the charge transition of D3, and the solid line represents the charge transition of D4. Electron numbers are assigned by completely depleting electrons from the donor and then adding electrons each time the donor transition line is crossed. By sweeping R2 to a negative voltage, electrons are added to quantum dots D3 and D4. In contrast, gates G1-G4 are only electrostatically coupled to the quantum dots (not tunnel coupled), and by sweeping gates G1-G4 to a negative voltage, electrons are normally removed from the corresponding quantum dots D3-D4, respectively. 【0053】 Optimization of SLQD charge sensors for single-electron charge detection To optimize the SLQD charge sensor of device 50 for time-resolved charge detection of electrons confined in donor quantum dots, the main tunable experimental parameter is input reflectance power P in In an SLQD charge sensor, the sensor signal is P inIt saturates as a function of P. This can be intuitively understood by considering a periodic single-electron tunneling process that generates the dispersed signal 53. in When the voltage is large enough to completely cross the Coulomb peak, a full set of electrons is driven between L1 and SLQD52 each time the reflectance signal reverses polarity. Because there is no DC current path, the tunnel current is limited to two electrons per AC cycle. Therefore, the amplitude of the tunnel current is constrained by the Coulomb blockade. The measured signal is directly proportional to the tunnel current in the device and therefore also saturates. In the current measurement, to provide the optimal readout from the SLQD charge sensor, P is set to occur at the beginning of this signal saturation. in This is selected. 【0054】 Figures 6(a) to 6(c) show the charge detection response of the SLQD charge sensor for the first charge transition of D1, with respect to the gate voltage and input power P. in This is shown as a function of level. Figure 6(a) shows P below the saturation level. in It has a value of -115 dBm. Figure 6(b) shows P at the start of power saturation. in It has a value of -103 dBm. Figure 6(c) shows P in a saturated state. in It has a value of -95 dBm. Beyond the saturation point, increasing the input power does not return much signal, and the Coulomb peak begins to power broaden. To detect donor quantum dot electrons, the optimal balance between signal contrast and the power broadening of the Coulomb peak is obtained at the beginning of saturation. in A value is selected (i.e., P in (=-103dBm). 【0055】 Figure 6(d) shows the shift in the SLQD sensor response (V) caused by an electron charging event on quantum dot D1. M This indicates the size of the shift. The size of this shift depends on the electrostatic coupling between the SLQD sensor and the target qubit. In D1, V M = 7.1mV. 【0056】 Furthermore, V as a function of the distance d between the qubit and the SLQD charge sensor 52M The size of V is found to be 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 in which the distance d decreases slowly can reduce the number of SLQD charge sensors required in a quantum processing device. Furthermore, due to the strong electrostatic coupling between the SLQD sensor and the qubit D1, all P in Figure 6d in Value V M The width of the Coulomb peak is greater than the width of the Coulomb peak. Therefore, in this situation, the maximum signal contrast for detecting D1 is obtained by tuning to the top of the Coulomb peak rather than the side of the peak, which gives the best small signal sensitivity. This is called the strong response charge detection region and allows for binary on-off switching of the entire sensor signal during charge detection by SLQD. In device 50, as shown in Figure 6(b), P in At -103 dBm, all four donor quantum dots D1-D4 are in the strong response range, and therefore, in order to detect all four qubits, P in The same value of -103dBm is used. 【0057】 Figure 6(e) shows the maximum sensor contrast as P in This is shown as a function of P, and the values ​​in Figures 6(a), 6(b), and 6(c) are shown by the matching shapes of a star, a circle, and a square, respectively. in At >-103dBm, the maximum signal saturates, and exceeding this value causes power spreading without a significant increase in signal height. This is evident in the following experiment: in This further justifies the use of -103dBm. 【0058】 The maximum tunneling current that can flow at the reflectance frequency is: |I max |=|4(1-α)ef|, (1) The formula is given by , where α is the lever arm between lead 54 and SLQD sensor 52, e is the electron charge, and f is the frequency of the reflectance measurement signal. It should be noted that the saturation value when the reflectance measurement signal is applied to a gate that is not tunnel-coupled to an SLQD dot is 4αef. 【0059】 Direct distributed readout uses a single lead and two quantum dots. The differential lever arm Δα = (α1 - α2) is a scaling factor that performs the conversion between the voltage applied to the lead and the energy difference created between the first and second dots (dot 1 and dot 2), where α1 is the lever arm between lead and dot 1, and α2 is the lever arm between lead and dot 2. In direct distributed readout, signal saturation also occurs up to a value of 4Δαef. Since the lever arm is a positive value, α > Δα always holds for single-lead sensors, which explains why SLQD charge sensors can have higher sensitivity than direct distributed readout. 【0060】 In typical STM devices, the SLQD charge sensor is close enough to its electron reservoir (e.g., single lead 54 in the SLQD sensor 52 of device 50) for tunneling to occur, so (1-α) > Δα holds true for practical STM devices (e.g., typical values ​​are (1-α) about 0.5 and Δα about 0.05). In CMOS nanowire devices, α can be greater than 0.9 and Δα is about 0.3 to 0.72. Therefore, the quantum capacitance (Cq∝α) of the SLQD charge sensor is... 2 ) is directly related to the quantum capacitance (Cq∝Δα) of the dispersed sensor. 2 This is much larger than ) and explains the possibility of higher sensitivity charge detection in quantum processing devices. Equation 1 also shows that sensitivity can be improved by operating at higher frequencies, as increasing the reflectance frequency generates more signal. 【0061】 Single-shot electronic spin readout P inOnce optimized, SLQD charge sensors (such as sensor 52) can immediately perform single-spin-based single-shot qubit readout (i.e., electron spin readout). Experimentally, single-spin-based single-shot electron spin readout was performed at D1, D2, and D3 using SLQD sensor 52. At donor dot D4, the tunnel rate to R2 exceeded the measurement bandwidth, preventing readout. 【0062】 Figure 7 shows the results of this spin readout experiment under a specific set of settings. In particular, in this experiment, a magnetic field of 1.5 Tesla was applied to Zeeman split the electron spin states D1-D3. For each donor dot, three levels of pulses were performed along the SLQD transition line, and the levels are shown by stars in Figures 7(a), 7(c), and 7(e). The three-level pulse is essentially a voltage pulse with three constant voltage levels, and the pulse can be abruptly switched to one of these three voltage levels. Specifically, the three-level pulse sequence consists of a load phase that initializes a random electron spin state, followed by a readout phase in which the spin is measured projectively, and an empty phase in which an electron is emitted before the next pulse repetition. 【0063】 During the reading phase, the spin-up state tunnels into the reservoir, followed by the spin-down state tunneling back into the donor dot, generating a characteristic "blip" in the charge sensor response that is not present in the spin-down state. The pulse sequence for this experiment can be provided by an arbitrary waveform generator, and the waveform is programmed via a computing or processing device. For example, the computing or processing device could be a "central control system". 【0064】 The donor quantum dots D1, D2, and D3 are close enough to their respective reservoirs R1 / R2 to allow electron tunneling between the dots and their respective reservoirs. There is a potential barrier that electrons can overcome via quantum tunneling to move, for example, between D1 and R1, provided that an energy state is available. In spin readout, spin-up electrons have higher energy and tunnel through the potential barrier, while spin-down electrons cannot. 【0065】 In the readout phase of the first electron transition, if an electron is spin-up during the readout phase, it tunnels off from the donor, and after a short time, the spin-down electron tunnels back. 【0066】 D - If electrons are in a spin-up state during readout, spin-down electrons tunnel in from the reservoir to form a two-electron singlet state, and then spin-up electrons tunnel back into the reservoir. In both cases, the increase in spin-up electrons during the readout phase is registered as a signal blip. When electrons are in a spin-down state, electron tunneling does not occur, and therefore no blip is observed. 【0067】 Figure 7(a) shows V on a single SLQD52 line intersecting the first electron charge transition of D1. G1 and V G2 The swept gate-gate map is shown. By adding electrons to D1, the peak position of SLQD52 is VM = 7.1 mV (V M is V G1The shift is only (the mutual charging voltage from this perspective). Figure 7(b) shows an example of spin-up 71 and spin-down 72 traces of D1, showing single-shot readouts. The fidelity of the spin readouts was calculated by taking 5000 individual single-shot traces and was found to be FM = 81%. Fidelity is limited by the measurement bandwidth (set to approximately 80 kHz in this experiment), which was not high enough to capture the fastest tunneling events. Increasing the measurement bandwidth allows for faster events at the expense of a decrease in SNR (which also reduces fidelity). In this experimental setup, a maximum fidelity of 81% was found at 80 kHz. 【0068】 Figure 7(c) shows V on a single SLQD52 line intersecting the second electron charge transition of D2. G1 and V G2 The swept gate-gate map is shown. The electron tunnel rate (approximately 2.6 kHz) in the second electron transition was favorable, so in this experiment, D - Charge readout was performed. An example of a single-shot trace showing the difference between the spin-up signal (signal 73) and the spin-down signal (signal 74) is shown in Figure 7(d). Taking 5000 individual traces, a fidelity of FM = 95% was found in D2. This fidelity is also partially limited by the measurement bandwidth that filters out the fastest tunneling events (15 kHz in this experiment), as well as the relatively high electron temperature (approximately 280 mK). 【0069】 Figure 7(e) shows V on a single SLQD52 line intersecting the first electron charge transition of D3. G1 and V G2 The swept gate-gate map is shown. In this case, electrons tunnel between D3 and R2 (not R1 as in the previous case) during spin readout. Figure 7(f) shows an example of single-shot spin-up 75 and spin-down 76 traces of the corresponding D3. The fidelity in this case is F M The calculation yielded 95%, but this is limited by the same factor as D2. 【0070】 Figure 7(g) shows the gate-gate voltage map of quantum dot D4. In this donor quantum dot D4, the tunneling rate between the donor and reservoir was too fast for single-shot spin readout. Indeed, a weak signal can be observed due to the periodic driving of electrons between D4 and R2. This suggests that the tunneling rate is not negligible compared to the RF reflectance frequency (130 MHz). Figure 7(h) shows a magnified view of region 77 in Figure 7(g), highlighting the weak signal due to donor electron tunneling. Due to the fast tunneling rate, single-shot spin readout was not possible in quantum dot D4. 【0071】 Table I below summarizes the single-shot readout results from the four donor dots D1-D4. 【0072】 [Table 1] 【0073】 Long-range charge detection This section describes the sensor shift V as a function of the sensor-qubit distance d. M This section describes the investigation of scaling. First, the electrostatic coupling between the SLQD sensor 52 of device 50 and the qubit was simulated using the finite element method package COMSOL multiphysics. The simulation results are plotted in Figure 8(a), where the dotted line contour indicates that a charge event on the target qubit causes a sufficient V to shift the Coulomb peak of SLQD 52 from full signal (peak top) to <1% signal. M This indicates a region with a large P response (strong response threshold). The strong response region is defined as the region where >99% full on-off signal contrast is possible. Beyond this strong response boundary, P inMaximum readout contrast is achieved by reducing the Coulomb peak, biasing to the side of the Coulomb peak, or both. Qubits located within the footprint of this contour line 82 could generate full on-off switching of the sensor signal and be measured without any loss of fidelity due to distance from the sensor. 【0074】 Figure 8(b) shows the shift of the SLQD sensor response as a function of distance d from the center of the SLQD sensor in the device region including the sensor and patterned qubits (V M The plot of ) is shown. Simulated V M When fitted to the value (blue dot 83), V M is d 1.4±0.1 It was found to be directly proportional to , which is consistent with actual measurement data using device 50 (indicated by circle 84). Both the experimental and simulation results are 1 / d, as shown by curve 81 in Figure 8(b). 3 It is incompatible with scaling. 【0075】 Figure 8(c) highlights the effect of this scaling difference in long-range charge detection. The left panel shows the 1 / d difference from Figure 8(b). 1.4 Using the fit, the SLQD sensor measures V at distances of 52, 100, 200, and 300 nm. M This is estimated. The solid and dotted lines show the predicted positions of the SLQD Coulomb peaks at 0 electrons and 1 electron on the target qubit at a specified distance, respectively. Optimal P in Figure 6(b) in The shape of the sensor Coulomb peak is determined by fitting it to the experimental data line at the value (i.e., -103 dBm). The arrow in Figure 8c indicates the maximum sensor contrast for detecting the electron charge on the target. The right panel shows 1 / d from Figure 8(b). 3 Using Fit(81), V at 100, 200, and 300 nm from the sensor. M The estimated RF response is shown. In this case, V M The contrast decreases more rapidly with distance, and is at its lowest at 300 nm. 【0076】 To highlight the importance of this scaling in scalable quantum computing, the expected single-shot read fidelity is calculated as a function of d for qubits with the same parameters as the dot D3 of device 50. From the fit in Figure 8(b), V as a function of d M This is estimated and used to calculate the predicted signal contrast. Subsequently, the signal-to-noise ratio (SNR) is calculated using the noise measured in the experiment and then used to calculate fidelity. 【0077】 Figure 8(d) shows 1 / d 1.4±0.1 and 1 / d 3 The results for both are shown. Curve 86 is 1 / d 1.4±0.1 Corresponding to the result, the shaded region 87 is the outline of the uncertainty range. Curve 85 is 1 / d 3 Corresponding to the results, a faster decline in readout fidelity is observed. As observed in direct measurements of D3, at small d, the sensor is in the strong response range, has full on-off signal contrast, and both curves saturate at 95% fidelity. As is clear from this figure, qubits with the same characteristics as D3 (i.e., donor-based qubits with low metal gate accumulation) are observed in accumulation mode gate-defined devices at 1 / d 3 With scaling, we were able to measure from the SLQD sensor up to 300nm with over 90% spin readout fidelity compared to 130nm. 【0078】 Furthermore, in a linear array of tunnel-coupled donor qubits with a typical separation distance of 12 nm between adjacent qubits, a single SQLD placed in the center of the linear array can read out up to 50 qubits with over 90% fidelity, similar to D3 (i.e., donor-based qubits with low metal gate accumulation). This can be increased to >99% by optimizing the measurement setup to reduce electron temperature, operating the SLQD at higher frequencies, and using quantum-limiting Josephson parametric amplifiers. The equivalent number of qubits in an accumulation-mode gate-defined device (assuming 80 nm qubit separation and a 130 nm detection range) is approximately 3. This matches currently available experimental gate-defined arrays with 3-4 qubits per sensor. 【0079】 In this experiment, the relaxation time T1 of D3 at 1.5 Tesla was measured to be 11 seconds. Furthermore, other experiments with donor qubits have shown up to 30 seconds. Given the very long relaxation time T1 in donor qubits and recent advances in navigating charge states in large qubit arrays, it may be possible to sequentially measure 50 qubits with the same SLQD charge sensor without limiting fidelity. 【0080】 The above experimental results show that the electrostatic coupling between the sensor and the qubit is 1 / d when used with donor-type qubits and single-shot SLQD charge sensors. 3 In contrast to previous measurements on a linear array of storage mode gate-defined devices where the dependency was observed, 1 / d 1.4±0.1This demonstrates dependence. This scaling difference will have a significant impact on long-range qubit readout in future quantum processing devices where scalability is a critical consideration. The favorable distance scaling in low-metal gate density devices 50 suggests that the number of sensors per qubit can be significantly reduced in future large-scale quantum processing devices. Thus, crystalline donor qubits have a dual advantage: a) qubits can be detected from greater distances, and b) qubits can be fabricated at higher densities due to atomic-scale lithography resolution. These results are very promising for realizing large-scale quantum computing architectures with dramatically reduced sensor density in atomic-scale qubits. 【0081】 Combined with convenient separation detection, SLQD's small footprint and high sensitivity make it a promising sensor for scaling up donor-based atomic qubits in large-scale quantum processing devices. 【0082】 As used herein, the term “to have” (and its grammatical variations) is used in a comprehensive sense of “to possess” or “to include,” rather than in the sense of “consisting of only.” 【0083】 Those skilled in the art will recognize that numerous variations and / or modifications can be made to the invention as shown in specific embodiments without departing from the spirit or scope of the invention as broadly described. Therefore, these embodiments should be considered illustrative and non-limiting in all respects.

Claims

[Claim 1] A plurality of qubits arranged within a semiconductor substrate, where each qubit is based on the spin state of a quantum dot embedded in the semiconductor substrate, and each quantum dot consists of one or more donor atoms, A single-lead quantum dot (SLQD) charge sensor fabricated within the aforementioned semiconductor substrate, Multiple control gates configured to control the corresponding qubits and A quantum processing system including, The SLQD charge sensor is configured to measure the spin state of two or more qubits arranged within the detection range of the SLQD charge sensor. Quantum processing system. [Claim 2] The quantum processing system according to claim 1, wherein the detection range of the SLQD charge sensor is 300 nanometers or less. [Claim 3] The quantum processing system according to claim 1 or 2, wherein the optimal interqubit distance between two adjacent qubits is 5 to 45 nanometers. [Claim 4] The quantum processing system according to any one of claims 1 to 3, wherein each of the plurality of control gates is located in the same plane as the plane in which the corresponding qubit and the SLQD charge sensor are located. [Claim 5] The quantum processing system according to any one of claims 1 to 4, wherein the plurality of qubits are arranged in a one-dimensional linear array, and the SLQD charge sensor is positioned near the center of the one-dimensional linear array to measure the spin states of two or more qubits. [Claim 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. [Claim 7] The quantum processing system according to claim 5 or 6, wherein the SLQD charge sensor measures the spin state of up to 50 of the qubits in the one-dimensional linear array. [Claim 8] The quantum processing system according to any one of claims 1 to 4, wherein the plurality of qubits are arranged in a two-dimensional array, and the SLQD charge sensor is placed near the center of the two-dimensional array. [Claim 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 array. [Claim 10] The quantum processing system according to any one of claims 1 to 9, wherein the SLQD charge sensor measures the spin state of each qubit using a single-shot readout process. [Claim 11] The detection range of the SLQD charge sensor is directly proportional to the electrostatic coupling between the SLQD and the qubit on the donor base. The electrostatic coupling is 1 / d １．４±０．１ It is directly proportional to, where d is the distance between the SLQD charge sensor and the qubit. A quantum processing system according to any one of claims 1 to 10. [Claim 12] The quantum processing system according to any one of claims 1 to 11, wherein the SLQD charge sensor sequentially reads out the spin states of the two or more qubits. [Claim 13] The donor atom is phosphorus 31 ( ３１ P) A quantum processing system according to any one of claims 1 to 12, wherein the donor atom is a donor atom. [Claim 14] A step of providing a plurality of qubits arranged in a semiconductor substrate, wherein each qubit is based on the spin state of a quantum dot embedded in the semiconductor substrate, and each quantum dot consists of one or more donor atoms, The steps include providing a single-lead quantum dot (SLQD) charge sensor on a semiconductor substrate, The steps include providing a plurality of control gates configured to control the corresponding qubits, and A method for manufacturing a quantum processing system including, The SLQD charge sensor is configured to measure the spin state of two or more qubits located within the detection range of the SLQD charge sensor. method. [Claim 15] The method according to claim 14, wherein each quantum dot is a phosphorus 31 donor quantum dot, and the phosphorus 31 donor quantum dots are fabricated in silicon using atomic-precision hydrogen registrography.

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