Quantum processing elements and systems

Abstract

This disclosure provides a quantum processing device comprising: one or more functional nanowires, each functional nanowire being connected to at least one of a source and a drain; a sensing nanowire spaced apart from the one or more functional nanowires and connected to at least one of the source and drain; one or more gate electrodes capacitively coupled to each of the one or more functional nanowires; one or more electrodes capacitively coupled to the sensing nanowire; a floating coupler disposed between the one or more functional nanowires and the sensing nanowire and electrostatically coupling the one or more functional nanowires and the sensing nanowire; and a controller connected to one or more gates of the sensing nanowire and one or more gates of the one or more functional nanowires.

Description

[0001] This application claims priority to Australian Provisional Patent Application No. 2020900803, filed on March 16, 2020, the contents of which are incorporated herein by cross-reference. Technical Field

[0002] Various aspects of this disclosure relate to charge sensing, and particularly, but not exclusively, to charge sensing arrangements of quantum dot arrays. Background Technology

[0003] The inventors are aware of the developments described in this section. However, unless otherwise stated, any developments described in this section should not be considered prior art solely because they are included in this section or because such developments are known to those skilled in the art.

[0004] Large-scale quantum processing systems hold the promise of a technological revolution, potentially solving problems that traditional machines cannot. To date, several different structures, materials, and architectures have been proposed for implementing quantum processing systems and fabricating their fundamental information units (or qubits).

[0005] For example, one way to fabricate qubits is by using silicon quantum dots. Quantum dots are tiny systems confined in all three spatial dimensions, such as electrons confined in a semiconductor by an electric field defined by a gate and an insulating material. In one instance, quantum dots can be used... 28 An interface is formed between the Si substrate and the dielectric material. A confinement arrangement is used to confine one or more electrons in the silicon substrate to form a quantum dot, and a control arrangement (e.g., a gate) is formed on the dielectric material to control the confined electrons (e.g., by applying a voltage to tune the electron spin resonant frequency of the confined electrons). Techniques for fabricating such quantum dots and processing systems utilizing these quantum dots are described in international patent applications PCT / AU2014 / 000596 and PCT / AU2016 / 050713.

[0006] When several such quantum dots are fabricated in a manner that allows them to be spaced appropriately apart, quantum information can move through the quantum dot array via spin shuttle or exchange-mediated electronic coupling.

[0007] Quantum dots based on electron spin exhibit high control fidelity and can take full advantage of existing manufacturing technologies to fabricate metal-oxide-semiconductor field-effect transistors (MOSFETs), making them a popular choice for semiconductor-based quantum bits. Summary of the Invention

[0008] According to a first aspect, the present invention provides a quantum processing device comprising: one or more functional nanowires, each functional nanowire being connected to at least one of a source and a drain; a sensing nanowire spaced apart from the one or more functional nanowires and connected to the at least one of the source and drain; one or more gate electrodes capacitively coupled to each of the one or more functional nanowires; one or more gate electrodes capacitively coupled to the sensing nanowire; a floating coupler disposed between the one or more functional nanowires and the sensing nanowire and electrostatically coupling the one or more functional nanowires and the sensing nanowire; and a controller connected to one or more gates of the sensing nanowire and one or more gate electrodes of the one or more functional nanowires; wherein during operation, the controller is configured to apply a bias voltage to bias the one or more gate electrodes of the sensing nanowire and the gate electrodes of the one or more functional nanowires such that sensing quantum dots are formed in the sensing nanowires, and one or more functional quantum dots are formed in the one or more functional nanowires, and the sensing quantum dots sense charge changes in each of the one or more functional quantum dots.

[0009] According to some embodiments, the quantum processing system includes a functional nanowire and two gates associated with the functional nanowire.

[0010] In such embodiments, the floating coupler includes two floating gates.

[0011] During operation, in some embodiments, a potential difference is maintained between the sensing nanowire and one or more functional nanowires to form one or more functional quantum dots in one or more functional nanowires under a floating gate.

[0012] Furthermore, in some embodiments, the sensing nanowire is coupled to two gates, and the two gates are biased to the same voltage.

[0013] In order to form functional quantum dots in functional nanowires under a floating gate, in some embodiments, the voltages of the sensing nanowires and the functional nanowires are biased relative to each other.

[0014] In some other embodiments, the quantum processing system includes a functional nanowire coupled to multiple gates. In such cases, a floating coupler may be coupled to a sensing nanowire capacitance at one end, and at the other end, the floating coupler may include multiple branches, each branch forming a branch gate, wherein each branch is coupled to a functional nanowire capacitance.

[0015] Furthermore, in such embodiments, a potential difference is maintained between the sensing nanowire and the functional nanowire to form functional quantum dots under one or more branch gates of the floating coupler.

[0016] In some other embodiments, the quantum processing system includes multiple functional nanowires, each of which is coupled to two or more gates. In such cases, the floating coupler includes a trunk segment, multiple branch segments, and each branch segment includes one or more leaf gates, with the ends of the trunk segments coupled to sensing nanowires, while the leaf gates are coupled to the functional nanowires.

[0017] Furthermore, in such embodiments, a potential difference is maintained between each of the sensing nanowires and the functional nanowires to form functional quantum dots under one or more leaf gates of the floating coupler.

[0018] According to another aspect of this disclosure, a method for controlling the operation of a quantum processing system is provided. The quantum processing system includes: one or more functional nanowires; a sensing nanowire spaced apart from the one or more functional nanowires; one or more gate electrodes capacitively coupled to each of the one or more functional nanowires; and one or more electrodes coupled to the sensing nanowire; a floating coupler disposed between the one or more functional nanowires and the sensing nanowire and electrostatically coupling the one or more functional nanowires and the sensing nanowire; and a controller connected to one or more gates of the sensing nanowire and one or more gates of the one or more functional nanowires. The method includes: receiving a current reading from a sensing nanowire at a controller; determining a bias voltage to be applied to one or more gates of the sensing nanowire based on the received current reading; determining a bias voltage to be applied to one or more gates of one or more functional nanowires based on the received current reading; applying the determined bias voltage to one or more gates of the sensing nanowire; and applying the determined bias voltage to one or more gates of the one or more functional nanowires; wherein the bias voltage is determined such that a sensing quantum dot is formed in the sensing nanowire and one or more functional quantum dots are formed in the one or more functional nanowires, and the sensing quantum dot senses a charge transition event in each of the one or more functional quantum dots.

[0019] In some embodiments, wherein the quantum processing system includes a functional nanowire coupled to two gates, and the floating coupler includes two floating gates, a second aspect of the method maintains a potential difference between the sensing nanowire and one or more functional nanowires to form one or more functional quantum dots in one or more functional nanowires under the floating gates.

[0020] In such embodiments, the sensing nanowire may be coupled to two gates, and the method includes determining and causing the same bias voltage to be applied to the two gates of the sensing nanowire.

[0021] In some embodiments, a second aspect of the method includes biasing the voltages of the sensing nanowires and the functional nanowires relative to each other to form one or more functional quantum dots in one or more functional nanowires.

[0022] In some other embodiments, the quantum processing system includes a functional nanowire coupled to a plurality of gates, and at one end, a floating coupler is coupled to a sensing nanowire, and at the other end, the floating coupler includes a plurality of branches, each of which is coupled to the functional nanowire. A second embodiment of the method includes biasing the voltages of the sensing nanowire and the functional nanowire relative to each other to form functional quantum dots under one or more branches of the floating coupler.

[0023] In yet another embodiment, the quantum processing system includes a plurality of functional nanowires, each functional nanowire including two or more gates, and the floating coupler includes a trunk segment, a plurality of branch segments, each branch segment including one or more leaf gates, and the ends of the trunk segments are coupled to sensing nanowires, while the leaf gates are coupled to the functional nanowires. A second aspect of the method includes biasing the voltage of each of the functional nanowires relative to the sensing nanowires to form functional quantum dots under one or more leaf gates of the floating coupler. Attached Figure Description

[0024] Figure 1 An example of prior art arrangement for sensing charge events of a quantum dot array using a single electronic transistor dot.

[0025] Figure 2 Existing technology arrangements for using sensing quantum dots and couplers to sense charge events of quantum dots.

[0026] Figure 3A A perspective view of an apparatus architecture for sensing charge events of multiple quantum dots using sensing quantum dots according to some aspects of this disclosure.

[0027] Figure 3B for Figure 3A A side cross-sectional view of the device architecture.

[0028] Figure 3C for Figure 3A A cross-sectional view of the other side of the device architecture.

[0029] Figure 4 A diagram illustrating the measured differential conductance of the SET used to increase the gate voltage.

[0030] Figure 5 For the purposes of this disclosure, some embodiments are described in detail below. Figure 3AA schematic diagram of the device architecture in which two functional quantum dots are formed simultaneously in one nanowire and a sensing quantum dot is formed in another nanowire.

[0031] Figure 6 A graph showing the charge sensing response of a quantum dot as a function of the gate voltage applied to a remote nanowire.

[0032] Figure 7 For the purposes of this disclosure, some embodiments are described in detail below. Figure 3A A schematic diagram of the device architecture in which four functional quantum dots are formed in one nanowire and sensing quantum dots are formed in another nanowire.

[0033] Figure 8 To explain Figure 7 The curves of the charge sensing spectra of the four quantum dots.

[0034] Figure 9 For the purposes of this disclosure, some embodiments are described in detail below. Figure 3A A schematic diagram of the device architecture in which two functional quantum dots are formed in one nanowire and a sensing quantum dot is formed in another nanowire.

[0035] Figure 10 To explain Figure 9 The curves of the charge sensing spectra of the two functional quantum dots.

[0036] Figure 11 This is a schematic diagram of another embodiment of an apparatus architecture for sensing charge events of multiple quantum dots using sensing quantum dots, according to some aspects of this disclosure.

[0037] Figure 12 This is a schematic diagram of yet another embodiment of an apparatus architecture for sensing charge events of multiple quantum dots using sensing quantum dots, according to some aspects of this disclosure.

[0038] While the invention may take various modifications and alternatives, 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 description are not intended to limit the invention to the specific forms disclosed. They are intended to cover all modifications, equivalents, and alternatives that fall within the spirit and scope of the invention as defined by the appended claims. Detailed Implementation

[0039] Overview

[0040] Non-invasive charge sensing is a valuable tool for studying the electronic charge and spin states in nanostructured devices. It has been used to identify electron occupancy down to single-electron energy levels and has enabled single-spin readouts of confined single electrons in quantum dots. Furthermore, the sensing device can be used to sense fundamental charge transfer events occurring between quantum dots in multi-point structures.

[0041] Generally, the sensing device can be a remote electrometer. In some systems, charge sensing has been achieved by using quantum dot contacts (QPCs) or single-electron transistors (SETs) fabricated near the quantum dot as sensors. Both quantum dot contacts (QPCs) and single-electron transistors (SETs) have high transconductance, making them sensitive to their local electrostatic environment and thus excellent charge sensors.

[0042] QPCs can be readily integrated with lateral quantum dot structures formed in two-dimensional electronic layers in GaAs / AlGaAs, Si / SiGe, and Si metal-oxide-semiconductor devices. SETs have also been integrated with quantum dots in a variety of structures, including Ge / Si core / shell nanowires, carbon nanotubes, graphene, and Si MOS devices.

[0043] In some previously known systems, the SET is placed close to the quantum dot to induce capacitive coupling between them. For example, an SET may be placed adjacent to a quantum dot, such that each SET senses an individual quantum dot. However, since SETs can typically be larger than the quantum dots they sense, individual SETs are not very meaningful for quantum processing systems containing tens, hundreds, or even thousands of quantum dots (because fabricating individual sensing devices for each quantum dot would essentially increase the size of the quantum processing chip by two or three times).

[0044] To address some of these issues, some systems can utilize a common SET to sense charge changes in multiple quantum dots (e.g., three quantum dots). Figure 1 The document describes such a system. Specifically, Figure 1This illustrates an example system in which three quantum dots 104 are formed in a laterally confined region 106. The quantum dots 104 are formed by applying a bias that allows electrons to accumulate to a gate 102. Lateral confinement can be generated by an electric field created by an insulating material surrounding a barrier gate or nanowire. A top gate 108 accumulates an electron gas below it, allowing current to be measured after the path defined by the gate 108. The gate 110 is then set to the voltage of the barrier layer that forms the electron gas, defining a small region in which electrons can pass through and out, thus defining a single SET. A SET 112 is located near the confinement region 106, such that a SET is adjacent to a linear arrangement of multiple quantum dots and capacitively coupled to each of the quantum dots. While this architecture allows a single SET to sense multiple quantum dots, it has drawbacks.

[0045] For a large number of quantum dots in the same nanowire or confined region, the sensitivity of the SET decreases because the capacitive coupling between the quantum dots and the SET decreases as the distance between them increases. Therefore, there is an upper limit to the number of quantum dots that a single SET can sense using this architecture, which is fixed based on the quantum dot spacing and the sensitivity of the SET device.

[0046] To circumvent the trade-off between sensitivity and distance in quantum dot sensors (SETs), some designs utilize a floating conductive material between the quantum dot and the sensor, thereby allowing the distance to the quantum dot to be greater than [missing information]. Figure 1 The system allows the placement of SETs at the specified distances.

[0047] Figure 2 Explain the design of this alternative system. For example... Figure 2 As shown, a floating conductive material 206 is placed between a quantum dot 204 and a set 212. The quantum dot 204 is formed by a bias gate 202. A top gate 208 accumulates an electron gas beneath it, allowing current to be measured after the path defined by the gate 208. The gate 210 is then set to the voltage of a barrier layer that forms the electron gas, defining a small region in which electrons can pass in and out, thereby defining a single set. By increasing the length of the floating conductive material 206, the distance between the quantum dot and the set can be increased without reducing the capacitive coupling between the quantum dot 204 and the set 212. However, this design also suffers from some drawbacks.

[0048] In this design, a coupler 206 is placed between a sensor and a quantum dot. Therefore, if the quantum processing element comprises n quantum dots, then this design may require n sensing devices or SETs. This again affects the footprint of the quantum processing element—increasing the chip size. Furthermore, the capacitive coupling between the quantum dot 204 and the floating conductive material 206 is a function of the distance between the tip of the floating conductive material and the quantum dot. Therefore, in such designs, the quantum dot must be placed extremely close to the floating conductive material, thus imposing high constraints on such system architectures.

[0049] Embodiments of this disclosure relate to novel and inventive device architectures for sensing the charge states of multiple quantum dots. Specifically, the embodiments disclosed herein relate to charge sensing of quantum dots formed in a CMOS multi-gate nanowire device by electrostatically coupling the quantum dots to a remote single-electron transistor (SET) formed in a neighboring nanowire via a floating gate. Some of the embodiments disclosed herein can form auxiliary quantum dots under the floating gate by biasing the gate in the remote SET and / or the nanowire itself relative to the nanowire housing the quantum dots, and the SET can be used to sense charge transitions in all quantum dots, i.e., the initial set and the auxiliary sets.

[0050] Therefore, the system disclosed in this invention increases the number of quantum dots sensed by a single floating coupler and generates a strong capacitive coupling between the SET and each of the quantum dots. Furthermore, the disclosed device addresses the limitations associated with measurements based on tunneling through the dots and allows sensing of all charge transitions up to the last electron in each quantum dot.

[0051] These and other aspects of this disclosure will be described in detail in the following sections.

[0052] Instance device architecture

[0053] Figure 3 illustrates an example device architecture 300 for sensing charge changes in a plurality of quantum dots via remote SET, according to some embodiments of the present disclosure. Specifically, Figure 3A A perspective view depicting the device architecture 300. Figure 3B Describe the cross-sectional side view of the device architecture along the xz axis, and Figure 3C This describes a side view of the device architecture along the yz axis.

[0054] Device architecture 300 includes two parallel silicon nanowires 302A and 302B. In one embodiment, the silicon nanowires 302A and 302B are fabricated on a silicon substrate using silicon-on-insulator (SOI) technology, and more specifically, fully depleted silicon-on-insulator (FD-SOI) technology. For example, the silicon nanowires can be fabricated by etching on an oxide layer. 28The oxide layer is formed on a silicon substrate and is made of Si material. This oxide material is called an embedded oxide layer.

[0055] In device architecture 300, gate electrodes 304A and 304B are close to nanowire 302A, and gate electrodes 304C and 304D are close to nanowire 302B. Specifically, gate electrodes 304A, 304B, 304C, and 304D can be wound around the edges of the corresponding nanowires 302A and 302B, such that the oxide layer separates the gate from the corresponding nanowire and electrically isolates the gate from the nanowire.

[0056] All four gate electrodes are connected to a DC voltage source for electrostatic control of the qubits formed under the gates. In addition to these four gates, device architecture 300 also includes uncontacted gates 306A and 306B, which approach (e.g., partially wound around) two nanowires in a manner similar to that of gates 304A to 304D. Uncontacted gates 306A and 306B act as floating couplers between nanowires 302A and 302B, thereby enhancing electrostatic coupling between the nanowires.

[0057] In some embodiments, the gate electrodes 304A to 304D and 306A-B may be made of polysilicon. However, it should be understood that, without departing from the scope of this disclosure, the gate may also be made of other suitable materials, such as aluminum, tantalum, tantalum nitride, tungsten, titanium nitride, palladium, and platinum.

[0058] Two silicon nanowires 302A and 302B can be connected to independent source electrodes (e.g., source electrodes 308A and 308B) and independent drain electrodes (e.g., drain electrodes 310A and 310B). Furthermore, the electrostatic potential of each of the two nanowires is controlled by its corresponding gate—nanowire 302A is controlled by gates 304A and 304B, and nanowire 302B is controlled by gates 304C and 304D.

[0059] During operation, a sensing quantum dot or SET is formed in one of the nanowires, and a functional quantum dot is formed in the other nanowire. For ease of reference, it is assumed that the sensing quantum dot is formed in nanowire 302B and the functional quantum dot is formed in nanowire 302A. However, it should be understood that this is merely an example, and the placement of the sensing and functional quantum dots can be interchanged, such that the sensing quantum dot is formed in nanowire 302A and the functional quantum dot is formed in nanowire 302B.

[0060] In any case, a sensing quantum dot is formed by applying a positive voltage to gates 304C and 304D to accumulate a large number of electrons under gates 304C and 304D. This accumulation of electrons under gates 304C and 304D enables the sensing quantum dot to be formed under gates 304C and 304D.

[0061] The sensitivity of the quantum dot sensing is a function of the transconductance of the sensing nanowire 302B, which is adjusted by biasing the SET gate (e.g., gates 304D and 304C) relative to the nanowire drain 310B.

[0062] Therefore, during operation, the gate voltages for the 304C and 304D are set such that the current changes more dramatically with small changes in the electrostatic environment at the sensing point. Figure 4 Figure 400 illustrates the differential conductance in micro-Siemens (μS) of nanowire 302B used to increase the gate voltages 304C and 304D between 0.5V and 0.65V. As seen in this figure, when the gate voltage is approximately 0.6V, subthreshold Coulomb oscillations, indicating the formation of said points, occur in the quantum dots under gates 304C and 304D. The square in Figure 400 indicates the current I. SDR The optimal sensitivity point for changes in point chemical potential, which can be used for charge sensing of any quantum dot formed in nanowire 302A.

[0063] Furthermore, in some embodiments, a constant bias of approximately 1 mV (or between 0 mV and 2 mV) is applied between the source 308B and drain 310B of the sensor nanowire 302B. This small bias ensures that the current in the sensing quantum dot always flows in the same direction.

[0064] To form functional quantum dots on nanowire 302A, a voltage is applied to gates 304A and 304B to draw electrons from gates 304A and 304B. In some embodiments, the voltage applied to gates 304A and 304B may be in the range of 0.1V to 1V.

[0065] Figure 5 This diagram illustrates how, when an appropriate bias voltage is applied to all gates of device 300, quantum dots 502 and 504 are simultaneously formed under gates 304A and 304B of nanowire 302A, and a large sensing quantum dot is formed in nanowire 302B under both gates 304C and 304D. (See diagram below.) Figure 5 As described, controller 508 can be used to apply a bias voltage to gates 304A, 304B, 304C, and 304D. Controller 508 can also be configured to receive current (If) from nanowire 302B. SDR The controller 508 may control the bias voltage for the gate based on the input current value in some embodiments. The controller 508 may be a software controller or a hardware controller.

[0066] In this operating state, any change in the charge distribution in nanowire 302A affects the chemical potential of sensing quantum dot 506 in nanowire 302B via floating electrostatically coupled gates 306A and 306B. Charge transitions can be observed via transport spectroscopy (measured via source-drain current of 302A) or via charge sensing (via SET current of 302B). This allows monitoring of quantum dots 502 and 504 up to the last electron. In other words, when the gate voltage of gates 304A and / or 304B changes, the number of electrons accumulated under the corresponding gate changes; that is, more electrons are drawn under the corresponding gate as the voltage increases, and the number of electrons accumulated under the corresponding gate decreases as the voltage decreases. Whenever the number of electrons under gates 304A or 304B changes, the charge sensing operating point of sensing quantum dot 506 shifts. Therefore, any change in the charge accumulated in nanowire 302A can be detected by the corresponding change in the current experienced by sensing quantum dot 506 in nanowire 302B.

[0067] Furthermore, based on the response of the charge sensor readings to changes in the gate voltages of gates 304A and 304B, it can be determined whether changes in the sensitivity of the quantum dot 506 respond to changes in quantum dots 502 or 504. For example, Figure 6 The charge sensing response of the quantum dot varies with the gate voltage V 304A and V 304B The graph shows the changes in electron count. More vertical lines in this graph correspond to electrons added to quantum dot 502, while more horizontal lines correspond to electrons added to quantum dot 504. In each case, the addition or removal of electrons from the quantum dot in nanowire 302A is detected via changes in current through sensor point 506. When the tunneling rate between the quantum dot and the reservoir (source or drain) becomes too slow, the visibility of certain charge transitions decreases. For example, this is seen in the portion of the graph corresponding to 0 to 0.5 V on the x and y axes.

[0068] In some embodiments, during operation, two additional quantum dots may be formed on nanowire 302A. These two additional quantum dots are formed under floating gates 306A and 306B, and are formed by creating a potential difference between nanowires 302A and 302B. Furthermore, if the electrostatic potential of the sensing nanowire (i.e., nanowire 302B) is higher than that of the functional nanowire (i.e., nanowire 302A), then the sensing nanowire can induce electrons to accumulate under gates 306A and 306B, where the gate capacitance is coupled to the functional nanowire 302A, thereby forming quantum dots in the functional nanowire 302A under 306A and 306B.

[0069] Figure 7This is a schematic diagram illustrating the formation of four functional quantum dots in nanowire 302A and the formation of sensing quantum dots in nanowire 302B. As can be seen in the figure, the four functional quantum dots include quantum dots 502 and 504, and quantum dots 702 and 704, formed under gate-coupled gates 306A and 306B.

[0070] Figure 8 Graph 800 illustrates the charge sensing spectra of the four quantum dots (i.e., dots 502, 504, 702, and 704). As seen in the graph, all charge transitions are identifiable because they differ from the electrostatic coupling of gates 304A and 304B and from the sensor quantum dot 506, resulting in different angles and contrasts in the color graphs (the color scale is the same in both graphs). The transitions with lower contrast at more vertical and horizontal angles in charge sensing refer to changes in the number of electrons at the dots under gates 304A (horizontal) and 304B (vertical). The transitions with higher contrast at intermediate angles refer to the addition of electrons to quantum dots 702 (more horizontal) and 704 (more vertical). The transitions corresponding to the quantum dots under gates 304A and 304B are almost perpendicular to their respective axes because these quantum dots have stronger coupling to the bias gate, while the transitions corresponding to the quantum dots under coupled gates 306A and 306B have intermediate angles because these quantum dots have weaker coupling to the bias gate. Secondly, the transitions of quantum dots 702 and 704 have a higher signal-to-noise ratio compared to those of quantum dots 502 and 504 because quantum dots 702 and 704 are more strongly coupled to the sensor nanowire 302B, again mediated by floating gates 306A and 306B. The white areas in graph 800 represent transitions where electrons move away from the SET sensor rather than towards it. This can occur, for example, when electrons move from quantum dot 704 to quantum dot 504, effectively moving negative charges away from the sensor. For all other, darker transitions, electrons are added from the source or drain reservoir, effectively moving negative charges towards the sensor. This is a common technique known in this art for identifying the direction of charge movement.

[0071] Generally, any form of orbital or valley degeneracy is detrimental to quantum computing, potentially leading to rapid spin relaxation and disrupting exchange coupling between spins. In the case of spin qubit readout, the added degree of freedom can hinder spin blocking. To a priori guarantee the absence of unwanted degeneracy, a good understanding of the point's electronic structure is necessary, which can be extremely challenging for many electronic qubits. In specific instances of extremely small, highly symmetric quantum dots, it is possible to identify the point's shell structure and treat electron interactions as small perturbations, similar to the situation in atomic physics. In more general cases, such as corner points in nanowires, the electronic structure and excitation spectra may not have easily identifiable characteristics in terms of quantum numbers. Under these conditions, operation at low electron occupancy rates is required.

[0072] In view of this, in some embodiments, instead of forming four quantum dots on nanowire 302A, two quantum dots may be formed, for example, under gates 304A and 306B. Figure 9 The image illustrates this formation of two quantum dots. In some embodiments, this can be achieved by completely depleting the quantum dots formed under gates 304B and 306A and accumulating some electrons under gates 304A and 306B. Figure 10 The diagram illustrates the charge stability of this configuration, and it indicates a well-defined dual quantum dot formation with identifiable charge configurations of various point occupancy rates of interest for quantum computing.

[0073] Figures 3 to 10 illustrate a dual nanowire structure, where a sensing quantum dot on one nanowire can be used to sense charge changes in up to four functional quantum dots on the other nanowire. However, it should be understood that this concept of electrostatically coupling nanowires via floating couplers and sensing functional quantum dots on the other nanowire via a sensing quantum dot on one nanowire can be extended to a large number of quantum dots. Figure 11 and 12 This describes the structure of two such instances.

[0074] Alternative architecture

[0075] Figure 11 An example device architecture 1100 for extending quantum processing systems is shown. Similar to device architecture 300 shown in Figure 3, this device architecture includes two nanowires: a sensing nanowire 1102 and a functional nanowire 1104. Each nanowire includes an independent source and drain. Furthermore, the sensing nanowire 1102 includes one or more gates. Figure 11A gate, namely gate 1105, is shown, and the functional nanowire 1104 includes a plurality of gates 1107A to 1107N. Two nanowires are electrostatically coupled to each other via a floating coupler 1106. The floating coupler 1106 includes a floating gate spanning between the sensor nanowire 1102 and the functional nanowire 1104. One end of the floating coupler is coupled to the sensing nanowire 1102, while the other end of the floating coupler 1106 has a plurality of branches 1108A-N wound around the edge of the functional nanowire 1104. In one embodiment, the number of these branches 1108 of the floating coupler 1106 may be equal to the number of gates 1107A-N of the functional nanowire 1104. Furthermore, in some embodiments, the branches 1108 may be wound around the edge of the functional nanowire 1104 at approximately the same longitudinal position as the gates 1107. In other embodiments, the branches may be wound around the edge of the functional nanowire 1104 at different longitudinal positions.

[0076] During operation, functional quantum dots 1110 may be formed under one or more of gates 1107 and 1108, as described above with respect to device architecture 300. Additionally, sensing quantum dots 1112 may be formed under gate 1105. In this manner, device architecture 1100 allows a single SET charge sensor 1112 to be electrostatically coupled to a number of functional quantum dots 1110 over a considerable distance.

[0077] Figure 12 This describes another example device architecture 1200 for extending quantum processing systems.

[0078] This device architecture includes multiple functional nanowires—see nanowires 1202, 1204, and 1206, and sensing nanowire 1208. Each nanowire may have its own independent source and drain. Furthermore, similar to sensing nanowires 302B and 1102, sensing nanowire 1208 includes one or more gates 1210. Each of the functional nanowires 1202 to 1206 includes multiple gates 1211. The nanowires are electrostatically coupled via floating gates 1212, which span between the sensing nanowire 1208 and the multiple functional nanowires 1202 to 1206.

[0079] In this device architecture, the floating coupler 1212 has a tree-like structure including a trunk, branches, and leaves. The trunk end of the floating coupler 1212 is wound around the edge of the sensing nanowire 1208, and multiple branches of the floating coupler (three in this embodiment) are wound around the edges of three functional nanowires. Each branch terminates at a leaf gate 1213, which may correspond in number to and be aligned with the gate of the corresponding functional nanowire. However, this is not always the case, and in some embodiments, the number or position of the leaf gates may not correspond to the number and / or position of the gates of the corresponding functional nanowires.

[0080] During operation, sensing quantum dot 1214 may be formed under the gate of sensing nanowire 1208, and functional quantum dots 1216 may be formed under one or more of gate 1211 and leaf gate 1213 (e.g., using the process described with respect to Figures 3 to 10). Furthermore, sensing quantum dot 1214 may be electrostatically coupled to each of the functional quantum dots 1216, enabling it to sense any charge events (or charge changes) among these functional dots. Therefore, in this embodiment, device architecture 1200 allows for the coupling of sensing quantum dots to multiple quantum dots residing in multiple nanowires.

[0081] The architectures described to date utilize floating couplers to electrostatically couple sensing nanowires to one or more functional nanowires. In other embodiments, floating couplers can be used to couple two or more functional nanowires to each other. For example, a floating coupler (each nanowire having one or more functional quantum dots) can be used between two functional nanowires to electrostatically couple the two functional nanowires. In another example, a floating coupler can be used to couple two clusters of quantum nanowires. In this example, a floating coupler can be used between the ends of the two clusters to electrostatically couple quantum dots in one cluster to quantum dots in the other cluster.

[0082] It should be understood that the architecture described in the above embodiments utilizes electrons in quantum dots. In other embodiments, quantum dots may be configured to confine holes instead of electrons.

[0083] The term “include” (and its grammatical variations) as used herein is used in the inclusive sense of “having” or “containing” rather than in the sense of “consisting of only”.

[0084] Those skilled in the art will understand that many variations 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 generally described. Therefore, the embodiments of the invention should be considered illustrative rather than restrictive in all respects.

Claims

1. A quantum processing system, comprising: One or more functional nanowires, each functional nanowire being connected to at least one of the source and drain electrodes; Sensing nanowires, which are spaced apart from the one or more functional nanowires and connected to at least one of the source and drain electrodes; One or more gate electrodes, which are capacitively coupled to each of the one or more functional nanowires; One or more electrodes coupled to the sensing nanowire capacitance; as well as A floating coupler is disposed between and electrostatically couples the one or more functional nanowires and the sensing nanowire, the floating coupler partially overlapping each of the one or more functional nanowires and the sensing nanowire. as well as A controller connected to one or more gates of the sensing nanowire and one or more gates of the one or more functional nanowires; During operation, the controller is configured to apply a bias voltage to bias the gates of the sensing nanowire and the gates of the one or more functional nanowires, such that sensing quantum dots are formed in the sensing nanowire and one or more functional quantum dots are formed in the one or more functional nanowires, and the sensing quantum dots sense charge changes in each of the one or more functional quantum dots.

2. The quantum processing system of claim 1, wherein the quantum processing system comprises a functional nanowire and the functional nanowire comprises two gates.

3. The quantum processing system of claim 2, wherein the floating coupler comprises two floating gates.

4. The quantum processing system of claim 3, wherein during operation, a potential difference is maintained between the sensing nanowire and the one or more functional nanowires to form one or more functional quantum dots in the one or more functional nanowires under the floating gate.

5. The quantum processing system according to any one of claims 1 to 4, wherein the sensing nanowire comprises two gates and the two gates are biased to the same voltage.

6. The quantum processing system of claim 4, wherein, in order to form the functional quantum dot in the functional nanowire under the floating gate, the voltages of the sensing nanowire and the functional nanowire are biased relative to each other.

7. The quantum processing system of claim 1, wherein the quantum processing system comprises a functional nanowire and the functional nanowire comprises a plurality of gates.

8. The quantum processing system of claim 7, wherein at one end, the floating coupler is coupled to the sensing nanowire, and at the other end, the floating coupler comprises a plurality of branches, wherein each branch is coupled to the functional nanowire.

9. The quantum processing system of claim 8, wherein a potential difference is maintained between the sensing nanowire and the functional nanowire to form a functional quantum dot in one or more branches of the floating coupler.

10. The quantum processing system of claim 1, wherein the quantum processing system comprises a plurality of functional nanowires and each functional nanowire comprises two or more gates.

11. The quantum processing system of claim 10, wherein the floating coupler comprises a trunk segment, a plurality of branch segments, and each branch segment comprises one or more leaf gates, and the end of the trunk segment is coupled to the sensing nanowire, while the leaf gate is coupled to the functional nanowire.

12. The quantum processing system of claim 11, wherein a potential difference is maintained between each of the sensing nanowires and the functional nanowires to form a functional quantum dot under one or more of the leaf gates of the floating coupler.

13. A method for controlling operation of a quantum processing system, the quantum processing system comprising: One or more functional nanowires; Sensing nanowires, which are spaced apart from the one or more functional nanowires; One or more gate electrodes, which are capacitively coupled to each of the one or more functional nanowires; And one or more electrodes, which are coupled to the sensing nanowire capacitance; A floating coupler is disposed between and electrostatically couples the one or more functional nanowires and the sensing nanowire, the floating coupler partially overlapping each of the one or more functional nanowires and the sensing nanowire. The method includes: a controller connected to one or more gates of the sensing nanowire and one or more gates of the one or more functional nanowires; and a controller connected to one or more gates of the sensing nanowire and the one or more functional nanowires. At the controller, current readings are received from the sensing nanowires; The bias voltage to be applied to the one or more gates of the sensing nanowire is determined based on the received current readings; The bias voltage to be applied to the one or more gates of the one or more functional nanowires is determined based on the received current readings. Apply the determined bias voltage to the one or more gates of the sensing nanowire; and Apply the determined bias voltage to the one or more gates of the one or more functional nanowires; The bias voltage is determined such that a sensing quantum dot is formed in the sensing nanowire, one or more functional quantum dots are formed in the one or more functional nanowires, and the sensing quantum dot senses a charge transition event in each of the one or more functional quantum dots.

14. The method of claim 13, wherein the quantum processing system comprises a functional nanowire, the functional nanowire comprises two gates, and the floating coupler comprises two floating gates.

15. The method of claim 14, further comprising maintaining a potential difference between the sensing nanowire and the one or more functional nanowires to form one or more functional quantum dots in the one or more functional nanowires under the floating gate.

16. The method of any one of claims 13 to 15, wherein the sensing nanowire comprises two gates, and wherein the method comprises determining and causing the same bias voltage to be applied to the two gates of the sensing nanowire.

17. The method of claim 15, further comprising biasing the voltages of the sensing nanowire and the functional nanowire relative to each other to form the one or more functional quantum dots in the one or more functional nanowires.

18. The method of claim 13, wherein the quantum processing system comprises a functional nanowire and the functional nanowire comprises a plurality of gates, and wherein at one end, the floating coupler is coupled to the sensing nanowire, and at the other end, the floating coupler comprises a plurality of branches, wherein each branch is coupled to the functional nanowire.

19. The method of claim 18, further comprising: The voltages of the sensing nanowire and the functional nanowire are biased relative to each other to form functional quantum dots under one or more of the branches of the floating coupler.

20. The method of claim 13, wherein the quantum processing system comprises a plurality of functional nanowires, each functional nanowire comprising two or more gates, and wherein the floating coupler comprises a trunk segment, a plurality of branch segments, each branch segment comprising one or more leaf gates, and the end of the trunk segment is coupled to the sensing nanowire, while the leaf gates are coupled to the functional nanowires.

21. The method of claim 20, further comprising the following steps: The voltage of each of the functional nanowires is biased relative to the sensing nanowire to form a functional quantum dot under one or more of the leaf gates of the floating coupler.

Images