Topological quantum computing components, systems, and methods

Abstract

A qubit device includes a crystal affixed to a substrate and in contact with an electrode. The crystal exhibits charge pair symmetry, and an electronic current moves in either a clockwise, counterclockwise, or both directions. An input current can be placed in a superposition state, where the current is unknown before being measured, and the direction of the current is measured to produce a binary output corresponding to a logical zero or a logical one. The state of the qubit device is monitored by measuring a voltage, a current, or a magnetic field, and assigning a superposition state or a ground state depending on a threshold.

Description

[0001] Statement Regarding Federally Funded Research:

[0002] This invention was made with Government support under Contract Nos. FA9550-16-1-0328 and FA8649-19-PA-435 awarded by the U.S. Air Force and under Contract Nos. NNX16CJ30P and 80NSSC18C0003 awarded by NASA. The Government has certain rights in this invention.

[0003] Related applications:

[0004] This application claims priority to US 62 / 924,150, filed on October 21, 2019. Technical Field

[0005] The present invention generally relates to quantum bits and quantum computing systems and methods. More specifically, the present invention relates to topological quantum bits (qubits), quantum registers including qubits, and computing systems and methods including topological qubits. Background Art

[0006] Quantum computing is a rapidly developing field in which quantum mechanical phenomena such as superposition and entanglement are used to perform certain types of calculations. Quantum computer circuits are based on quantum bits (also known as "qubits" or "qbits"), which are the basic units of information in quantum computers. A qubit can exist in two states, 0 or 1, at the same time or at different times. Multiple qubits are functionally coupled to form quantum registers, which are roughly the quantum analog of classical processor registers. Quantum logic gates (or quantum gates) are basic quantum circuits consisting of a small number of qubits that can be combined to form larger quantum computing circuits.

[0007] In order to stabilize qubits, they must be protected from external disturbances that could disrupt their quantum state, such as thermal and electromagnetic noise. In many cases, cryogenic temperatures close to absolute zero are required to protect them from such disturbances. Quantum computing is also limited by the short coherence time, or the length of time a prepared quantum state can be maintained for an existing qubit. This is at least in part because current quantum computing technology is based on entangling electrons, photons, or ions, which cannot be directly coupled to electronic components.

[0008] WO 2018 / 190919 A9 describes composite semiconductor nanoparticle compositions and assemblies that exhibit enhanced thermoelectric properties, including increased electrical conductivity, a Seebeck coefficient, and reduced thermal conductivity. The composite nanoparticle composition comprises: semiconductor nanoparticles comprising a front and back surface and sidewalls extending between the front and back surfaces; and metal nanoparticles that can be bonded to at least one of the sidewalls to establish a metal-semiconductor junction. The semiconductor nanoparticles may comprise, for example, molybdenum sulfide (MoS2), antimony telluride (Sb2Te3), or bismuth telluride (Bi2Te3), and may exhibit a bipyramidal structure. The metal nanoparticles can be bonded to one or more sidewalls of the semiconductor nanoparticles. Suitable metals include metals selected from Groups IVA-VIIIA and IB of the periodic table. In one example, silver nanoparticles are bonded to the sidewalls of Sb2Te3 nanoparticles, wherein the interface transition region comprises Sb2Te3-Ag2Te-Ag. Summary of the Invention

[0009] Embodiments of the present invention preferably seek to mitigate, alleviate or eliminate one or more deficiencies, shortcomings or problems in the art, such as those noted above, either singly or in any combination, by providing a qubit, a qubit register, a quantum computer, a method of making a qubit, a method of making a qubit register, and a method of making a quantum computer.

[0010] The inventors have discovered that at least some semiconductor nanoparticles of the type disclosed in WO 2018 / 190919 A9 can be used to form qubits, and that qubits comprising nanoparticles can operate at temperatures much higher than existing quantum bits, are less sensitive to interference, and have longer coherence times than existing materials used to form qubits. Furthermore, the state of qubits comprising certain types of semiconductor nanoparticles disclosed in WO 2018 / 190919 A9 can be measured using simpler and less expensive means than those required for existing quantum computers. The qubits described herein can also be used, for example, as components of atomic clocks, quantum navigation sensors, quantum key distribution systems, and entanglement-enhanced microscopes. Embodiments of qubits, registers, and logic gates can have micron-scale sizes, making them simpler and less expensive to manufacture and operate than existing quantum bits, registers, and logic gates. Furthermore, the state of the qubits can be measured using simpler and less expensive means than those required for existing quantum computers. Thus, the present invention enables quantum computing to be mobile, not limited to the cloud.

[0011] In one aspect, the present invention provides a qubit device comprising a semiconductor nanocrystal affixed to a substrate, wherein the nanocrystal has a superposition state or a basis state of electron flow associated with the nanocrystal.

[0012] In another aspect, the present invention provides a register comprising a plurality of qubit devices.

[0013] In yet another aspect, the present invention provides a method for monitoring the state of a qubit device comprising chiral nanocrystals.

[0014] In yet another aspect, the present invention provides a method for forming a quantum register comprising semiconductor nanocrystal qubits. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The elements of the drawings are not necessarily to scale relative to each other, emphasis instead being placed on clearly illustrating the principles of the present disclosure. Like reference numerals designate corresponding parts throughout the several views of the drawings, wherein:

[0016] Figure 1A is a top-down transmission electron micrograph of a transition metal dichalcogenide (TMD) nanoplatelet (or nanocrystal) of the type used to form qubits;

[0017] Figure 1B is a top-down scanning electron micrograph of a TMD nanoplatelet having silver nanoparticles bound to the edges of the nanoparticles along their central planes;

[0018] Figure 1C Two contrasting scaled-up images showing the interface between metal nanoparticles and TMD nanoplatelets;

[0019] Figures 2A-2E shows a sequence of events during the formation of TMD nanoplatelets and TMD nanoplatelets including metal nanoparticles;

[0020] Figure 3 is a schematic diagram showing the basic structure of one embodiment of a qubit;

[0021] Figure 4 is a photograph of a qubit comprising a nanoplatelet of the type shown in FIG1 ;

[0022] Figure 5 is a graph showing the voltage measured on a qubit of the present invention;

[0023] Figure 6 is a combined atomic force and confocal microscopy (AFM / CFM) image showing the configuration of the nanoplatelet edge; and

[0024] Figure 7 is a graph comparing the top and bottom side currents versus de-chipping time. DETAILED DESCRIPTION

[0025] Specific embodiments of the present invention are described with reference to the accompanying drawings. However, the present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete and will fully convey the scope of the invention to those skilled in the art. In the drawings, like reference numerals refer to like elements.

[0026] Unless otherwise specified, all domain-specific terms are assumed to have their accepted meanings in the field. Unless otherwise specified, all non-domain-specific terms are assumed to have their ordinary meanings in the context of their use.

[0027] As used herein, a nanoparticle or nanoplatelet is a particle having at least one dimension less than 1,000 nanometers or 1 micrometer in length.

[0028] Figure 1A and 1B A top-down transmission scanning electron micrograph of chiral, self-assembled bipyramidal Sb2Te3 transition metal dichalcogenide (TMD) nanoplatelets / nanocrystals (10). Figures 2A-2E The process of forming a TMD nanoplatelet (10) is shown. The nanocrystal (10) includes a top or front surface (11, Figure 3 ) and the back or bottom surface (12, Figure 3 ) and sidewalls (13) extending therebetween. The nanocrystals (10) can be produced using the solvent engineering process for forming self-assembled nanoparticles disclosed in WO 2018 / 190919 A9, incorporated herein by reference, and in particular for forming self-assembled nanoparticles of MoS2, Sb2Te33, and Bi2Te33. During the process, the lattice is formed around a central axis (14, Figure 2A ) are formed, and sequential layers (15) are formed that grow in opposite directions with opposite chirality, with clockwise and counterclockwise turns moving axially upward and downward from the center along the central axis, respectively. Without being bound by theory, it is believed that the complex topology of the nanoplatelet (10) imparts properties to the conductive channel that are not reflected in the base band structure of the nanoplatelet. Figure 6 The graph is based on AFM / CFM measurements, which show a slight elevation at the edge (13) of the sequential layer (15) not seen in the previously reported overall growth spiral. The region that appears elevated exhibits unexpected electron density of specific topological properties. The magnetic moment calculated using AFM / EFM (electrostatic force microscopy) measurements indicates that the field strength for the TMD nanoplatelet (10) is sufficient to achieve entanglement at room temperature.

[0029] The characteristic of these submicron-sized TMD nanocrystals (10) is that they can be defined by a spiral topological path to achieve the desired flow along the nanoparticle / nanoplatelet (10) ( Figure 3) at the edges of the top and bottom halves of the object. This provides a unique way to establish a superposition of two states at temperatures much higher than existing systems. The topological current runs from the fundamental habit plane (37) along the spiral of the top surface (11), along the central dislocation (not shown) to the top and back. This current does not cross the habit plane (37) onto the bottom half (12) because this would destroy the charge-parity symmetry. The topological state is charge-parity constant, so mirror currents are established in the two halves. Although the object is electrically neutral, for any given measurement, one current direction dominates, so that any measurement of the current along the outer edge (13) will give a + or - current that follows the spiral, and never zero. This established bistability of the state formed using topology is not currently predicted by topological quantum computing theory.

[0030] Figure 2D and 2E The formation of metal nanoparticles (21) along the central outer edge (22) of the nanoparticles from the metal ions (20) is shown. The presence of nanoparticle dopants such as silver, gold, platinum, copper and other Group IVA-VIIIA and Group IB metals can be used to form metal nanoparticles that bind to at least a portion of the outer edge (22) or other sidewalls (13) and establish a metal semiconductor junction that can be used to increase the electron density. For example, Bi2Te3 and Sb2Te3 nanoplatelets can be coated or doped with Ag nanoparticles by dispersing the nanoparticles in ethylene glycol and mixing with silver nitrate overnight at room temperature. The Ag-coated TMD nanoparticles can be recovered by washing with ethanol. Bi2Te3 and Sb2Te3 nanoplatelets (10) can be coated or doped with Cu nanoparticles by dispersing the nanoparticles in ethylene glycol and mixing with cuprous iodide and cuprous chloride overnight at 60°C. The Cu-coated TMD nanoparticles can be recovered by washing with ethanol. A magnified view of the Ag nanoparticles on the Sb2Te3 nanoplatelets is shown in FIG. Figure 1C In display.

[0031] Cross-structure coherence means that the wave function of the electron at the surface crosses the habit surface (37) ( Figure 3 ) are symmetric or antisymmetric. The topological complexity of these chiral nanoparticles / nanoflakes (10) produces charge parity protected states that interact to obtain stable entanglement between the top and bottom halves or top and bottom faces (11, 12) of the nanocrystal (10), each of which has a central upward current or a downward current. Thus, the nanocrystal (10) behaves as two halves or faces ( Figure 3The top spiral and the bottom spiral in the nanocrystal (10) are entangled to form an entangled object, so that the nanocrystal (10) can be used as a quantum bit or qubit for quantum computing. The moment projection at the central axis can be ↑ or ↓. For the counterclockwise topological current, the result is ↑ and V SD = +1 (for example). This means that ↓ is associated with clockwise current flow and V SD = -1. However, the top and bottom are correlated, and when a back gate (33) coupled to the bottom of the nanoparticle (10) is used to force a large magnetic or electric field across the entire structure, then the top and bottom surfaces (11, 12) must be in an entangled state.

[0032] Figure 3 is a diagram showing components of a qubit (30) according to one embodiment of the present invention. A voltage source lead (31) and a voltage drain lead (36) are positioned in contact with or nearly touching the surface of the top surface (11) of the nanoplatelet (10). These leads (31, 36) act as current sensing elements (300) for sensing the direction of electron current on the top surface (11) of the nanocrystal (10). A back gate lead / electrode (33) is positioned in contact with or nearly touching the surface of the bottom surface (12) of the nanoplatelet (10). The back gate electrode (33) can be pulsed to place the nanocrystal in a state of superposition relative to the electron current. The direction of the current is conveniently determined using an electric field measurement such as the direction of a voltage drop using the electrodes (31, 36). Additionally or alternatively, the direction of the current can be measured using other current sensing members (300), such as superconductors or magnets, which are positioned in juxtaposition with the top of the nanoparticle to measure the magnetic field induced by the current. Additionally or alternatively, the current sensing means (300) may include an electromagnetic sensor for measuring the absorption or reflection of circularly polarized light by the electric and / or magnetic fields induced by the electron current.

[0033] Figure 4is a photograph of an actual qubit comprising a TMD nanocrystal (10) anchored on an insulating layer (41, not shown) above a gate electrode (33) formed on a non-conductive substrate (40), which may be made of silicon with an oxide surface or other suitable non-conductive material. In this example, the back gate electrode (33) contacts the bottom surface (12) of the nanocrystal (10). A first electrode providing a voltage source (33) contacts a first location on the outer edge of the top surface (11) of the nanoparticle (10), and a second electrode providing a voltage drain (36) contacts a second location on the outer edge of the top surface (11) of the nanoparticle (10). A third electrode providing a voltage source (34) contacts a first location on the outer edge of the bottom surface (12) of the nanoparticle (10), and a second electrode providing a voltage drain (35) contacts a second location on the outer edge of the bottom surface (12) of the nanoparticle (10). This can be achieved by adding an in-phase shift when applying the voltage and positioning the spikes in the measured voltage in one direction or the other (e.g. Figure 5 ) to measure the direction of the electron current in each of the top and bottom surfaces (11, 12).

[0034] The function of the electrodes can be changed by varying the applied voltage, and the position of the leads (33) and (36) on the upper half of the nanoparticle can be varied. Additional electrodes (32, 34, 35) are optional and can be used to apply and measure directional voltages, including phase-shifted voltages, on the nanoparticle (10), to provide functional redundancy, or to provide connections to additional qubits, sensors, and / or microprocessor controllers to coordinate reset and measurement times.

[0035] The minimum current required to measure the voltage depends on the sensitivity of the measuring device. The presence of silver nanoparticles or other nanoparticle dopants such as gold, platinum, copper, and other Group IVA-VIIIA and Group IB metals (21) can be used to form metal nanoparticles that bind to at least a portion of the outer edge (22) or other sidewalls and establish a metal semiconductor junction that can be used to increase the electron density (if necessary) to provide a reliable, measurable voltage. Figure 1C A close-up view of silver nanoparticles 21 on the edge 22 of a TMD nanocrystal (10) is shown. For any given qubit design, Hall measurements can be made to determine the detectable current level using a picoammeter, and the presence, type, or amount of dopant adjusted as needed to achieve the detectable current level.

[0036] Figure 7 Demonstrates the use of something similar to Figure 4Results of measurements made on a qubit device of the qubit device shown in FIG, wherein measurements were made simultaneously on both the top and bottom surfaces (11, 12) of the nanocrystal (10). A back gate (33) was pulsed by a microprocessor control element to place the nanocrystal in a superposition state, and measurements were made between the two top mounting leads (31, 36) and the two bottom mounting leads (34, 35). After superposition, an LHC / RHC ratio of 1:1 was maintained for 100 ms, indicating a coherence time of 100 ms at room temperature.

[0037] A qubit according to the present invention can be formed, for example, by the following operations: forming a gate electrode (33) on a non-conductive substrate (40); forming an insulating layer (41) above the gate (33); fixing a semiconductor nanocrystal (10) to the insulating layer (41) in contact with or juxtaposed with the gate electrode (33); and placing electrodes (31, 36) on or juxtaposed with the upper half (11) of the crystal. Additional leads (34, 35) can also be formed on the non-conductive substrate (40) before fixing the semiconductor nanocrystal (10) to the insulating layer (41).

[0038] Qubit devices can be combined to form a quantum register comprising multiple qubit devices entangled via coupling between the charge quanta of the qubits. The qubit devices are not directly physically connected, and the state of each qubit device is read simultaneously. The qubit devices can be used to form quantum gates, including Pauli gates and quantum logic gates, as well as to form quantum circuits. A significant advantage of qubits comprising doped TMD nanocrystals is that they do not require cryogenic cooling, as the qubits operate at temperatures up to and including room temperature, such as -80°C, -40°C-20°C, 0°C, 10°C, 20°C, and 25°C.

Claims

1. A qubit device comprising: Nanocrystals (10) fixed on a substrate (40); a back gate electrode (33) in contact with or juxtaposed with the bottom surface (12) of the nanocrystal (10); and an electron current sensing member configured to measure an electron current in the nanocrystal (10), in: The nanocrystal (10) has a superposition state or a basis state of an electronic current associated with the nanocrystal; The nanocrystal (10) includes charge pair symmetry, and the electron current moves in a habit plane (37) separating a top surface and a bottom surface of the nanocrystal in a clockwise, counterclockwise, or both directions; The current in the nanocrystal (10) can be placed in a superposition state using the back gate electrode (33) so that the electron current is unknown until it is measured by the electron current sensing means; as well as The direction of the electron current in the nanocrystal (10) can be sensed by the electron current sensing component to generate a binary output corresponding to logic zero or logic one.

2. The qubit device of claim 1 , wherein the electron current sensing means comprises: a first electrode (31) in contact with or juxtaposed with a first location on the top surface (11) of the nanocrystal (10), and a second electrode (36) in contact with or juxtaposed with a second location on the top surface (11) of the nanocrystal (10); in: The first electrode (31) and the second electrode (36) are configured to sense the direction of the electron current.

3. The qubit device of claim 1 , wherein the nanocrystals comprise transition metal dichalcogenides (TMDs).

4. The qubit device of claim 3, further comprising metal dopant nanoparticles (21) formed along a central outer edge (22) of the nanocrystal (10), wherein the metal is selected from the group consisting of: copper, silver, gold, and combinations thereof.

5. The qubit device of claim 1 , wherein the superposition state is generated from the basis state at a temperature between -80°C and 25°C.

6. The qubit device of claim 1 , further comprising two or more additional electrical leads in contact with or juxtaposed with the nanocrystals to provide functional connections to a controller and / or sensing element.

7. A quantum register comprising a plurality of qubit devices according to claim 1, the qubit devices being quantum entangled via coupling between charge quanta of the qubits, wherein the qubit devices are not directly physically connected.

8. A method for monitoring the state of a qubit device comprising a chiral nanocrystal (10), wherein: The qubit device is a qubit device according to any one of claims 1 to 6, the method comprising: measuring a voltage, current, or magnetic field of the qubit device; assigning a superposition state if the measured voltage, current, or magnetic field is less than a superposition threshold; and assigning a base state value if the measured voltage is greater than a base state threshold; The measured voltage, current or magnetic field corresponds to a clockwise or counterclockwise flow of electrons around the chiral nanocrystal.

9. A method for forming a qubit device according to any one of claims 1 to 6, the method comprising: forming a back gate electrode (33) on a non-conductive substrate (40); forming an insulating layer (41) above the back gate electrode (33); Fixing the bottom surface (12) of the semiconductor nanocrystal (10) to the insulating layer (41) and in contact with or juxtaposed with the back gate electrode (33); and Two electrodes are placed on or in juxtaposition with the top surface (11) of the semiconductor nanocrystal (10).

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