Quantum transistor

Abstract

The quantum computing device (22) includes an optical resonator (56) having a resonant wavelength band. A crystalline material (52) containing crystal defects (54) is contained within the optical resonator. The crystal defects have a ground state and an excited state having an emission wavelength in the resonant wavelength band. Source electrodes (64) and drain electrodes (66) are positioned opposite the crystal defects and configured to apply a first electric field to the crystalline material along the longitudinal axis. A gate electrode (68) is positioned close to the crystal defects and configured to apply a second electric field perpendicular to the longitudinal axis. A control circuit (34) applies a first voltage between the source electrodes and the drain electrodes to control the charge state of the crystal defects and applies a second voltage to the gate electrode to adjust the emission wavelength.

Description

[Technical Field]

[0001] This invention relates to quantum computing in general, and more particularly to solid-state qubits. [Background technology]

[0002] Quantum computers apply the principles of quantum physics to solve computational problems, potentially performing certain calculations far more efficiently than existing digital (classical) computers. The basic building block of a quantum computer is the qubit. Quantum computers are equipped with quantum gates constructed from qubits, including single-qubit gates, two-qubit gates, and multi-qubit gates.

[0003] To realize qubits, various different physical systems have been proposed and developed, including superconducting circuits, trapped ions and atoms, and solid crystal defects such as lattice vacancies in diamond and other semiconductor materials. This defect-based realization form has advantages in that compact qubits can be created in solids and operate down to room temperature (in other words, from 4K to 300K). Various different defect types have been proposed and evaluated for this purpose.

[0004] One of the most promising types of crystal defects for quantum computing is nitrogen vacancy (NV) color centers in diamond. To form an NV color center, carbon atoms in the diamond crystal lattice are replaced by nitrogen atoms, and further, adjacent carbon atoms are replaced by vacancies. This structure allows electrons from nearby carbon and nitrogen atoms to occupy the vacancies and form "artificial atoms." The charge of an NV center is negative (NV - ), neutral (NV 0 ), or positive (NV + ) could be any of the following. NV -Optical transitions between energy levels of a state, along with spin-dependent relaxation processes, are NV - This allows electron spins to be polarized even at room temperature by irradiating the color center with a green or blue laser beam. - The optical excitation of the color center has a zero phonon line (ZPL) wavelength of approximately 637 nm. 3 From the E triplet electron state 3 Transitions between A2 triplet electronic states result in red photoluminescent emission. The emission intensity depends on the degree of electron spin polarization, thereby providing a means for measuring electron spin polarization to perform quantum calculations.

[0005] In the context of this specification and in the claims, the terms “light emission” and “light” refer to electromagnetic radiation in any of the visible spectral range, the infrared spectral range, and the ultraviolet spectral range. [Overview of the project]

[0006] Embodiments of the present invention described below provide improved quantum computing devices and methods for implementing such devices.

[0007] Therefore, according to embodiments of the present invention, a quantum computing device is provided which includes an optical resonator having a resonant wavelength band. A crystalline material containing crystal defects is contained within the optical resonator. The crystal defects have a ground state and an excited state having an emission wavelength in the resonant wavelength band. Source and drain electrodes are disposed on opposite sides of the crystal defects and configured to apply a first electric field to the crystalline material along the longitudinal axis. A gate electrode is disposed in close proximity to the crystal defects and configured to apply a second electric field to the crystalline material perpendicular to the longitudinal axis. A control circuit is configured to apply a first voltage between the source and drain electrodes to control the charge state of the crystal defects and to apply a second voltage to the gate electrode to adjust the emission wavelength.

[0008] In the disclosed embodiments, the crystalline material includes diamond, and the crystal defect includes a nitrogen-vacancy (NV) defect. Application of a first voltage between the source electrode and the drain electrode switches the NV defect between the NV 0 state and the NV - state.

[0009] In some embodiments, application of a first electric field having a first polarity switches the crystal defect to a first charge state, and application of a first electric field having a second polarity opposite to the first polarity switches the crystal defect to a second charge state having a ground state and an excited state having an emission wavelength in a resonance wavelength band. In the disclosed embodiments, the control circuit is configured to apply a first voltage to maintain the crystal defect in the second charge state during a quantum calculation.

[0010] Additionally or alternatively, the device includes an optical waveguide configured to transmit one or more excitation beams to the crystal defect at wavelengths selected to convert one or more electron spin states of the crystal defect to respective charge states, and the controller is configured to detect the charge state of the crystal defect by measuring a current between the source electrode and the drain electrode.

[0011] Further additionally or alternatively, the optical waveguide is configured to transmit one or more excitation beams to the crystal defect, including a first excitation beam at a transition wavelength of the second charge state and a second excitation beam at an infrared wavelength selected to initialize the crystal defect in the second charge state while preventing conversion of the second charge state to the first charge state.

[0012] In the disclosed embodiments, the control circuit is configured to adjust a second voltage to adjust the emission wavelength of the crystal defect.

[0013] In some embodiments, the device includes a semiconductor donor layer disposed between at least one of the electrodes and the crystal defect. In one embodiment, the application of a second electric field creates a two-dimensional PIN structure over the crystal defect. In some embodiments, the semiconductor donor layer includes one or more of a transition metal oxide (TMO) and a transition metal dichalcogenide (TMD).

[0014] In one embodiment, the device includes a piezoelectric element coupled to change the length of the optical resonator, wherein the control circuit is configured to drive the piezoelectric element to adjust the resonance wavelength band of the optical resonator.

[0015] In some embodiments, the optical resonator includes a periodic structure formed in the crystal material on opposite sides of the crystal defect. In one embodiment, the periodic structure includes holes extending through a layer of the crystal material containing the crystal defect. In another embodiment, the periodic structure includes depressions on the surface of the crystal material.

[0016] In some embodiments, the crystal material is configured as an optical waveguide coupled to transmit optical radiation emitted from the crystal defect at the emission wavelength from the optical resonator to the detector. Generally, the optical waveguide is further coupled to transmit one or more excitation beams at one or more excitation wavelengths from one or more beam sources to the crystal defect.

[0017] In some embodiments, the device includes a substrate on which an optical waveguide is disposed; an input waveguide disposed on the substrate and coupled to inject one or more excitation beams into the optical waveguide; and an output waveguide disposed on the substrate and coupled to receive the light radiation emitted from the optical waveguide. In the disclosed embodiments, the optical waveguide, as well as the input and output waveguides, have tapered ends which are superimposed on the substrate to inject one or more excitation beams into the optical waveguide and to inject the light radiation emitted into the output waveguide by adiabatic coupling. Additionally or alternatively, the output waveguide includes a filter configured to block the excitation wavelength.

[0018] In the disclosed embodiments, the optical waveguide includes a ridge disposed on a slab of crystalline material. Alternatively or additionally, the optical waveguide has a cross-sectional profile selected from a group of profiles consisting of rectangular, triangular, and pentagonal profiles.

[0019] In some embodiments, the device includes a photonic integrated circuit (PIC) substrate on which a crystalline material is disposed, and one or more optical waveguides disposed on the substrate and optically coupled to the crystalline material. In the disclosed embodiments, one or more optical waveguides include at least one inverse taper configured to couple optical radiation between the crystalline material and the one or more optical waveguides. Alternatively, the PIC includes a reflective surface configured to couple optical radiation between the crystalline material and the one or more optical waveguides.

[0020] According to embodiments of the present invention, a method for quantum computing is also provided, comprising providing a crystalline material containing crystal defects within an optical resonator. The crystal defects have a ground state and an excited state having an emission wavelength in the resonant wavelength band of the optical resonator. Source and drain electrodes are positioned opposite the crystal defects to apply a first electric field to the crystalline material along the longitudinal axis. A gate electrode is positioned close to the crystal defects to apply a second electric field to the crystalline material perpendicular to the longitudinal axis. A first voltage is applied between the source and drain electrodes to control the charge state of the crystal defects, and a second voltage is applied to the gate electrode to adjust the emission wavelength.

[0021] The present invention will be better understood from the following detailed description of its embodiments, which is made together with the drawings. [Brief explanation of the drawing]

[0022] [Figure 1] This is a block diagram schematically showing a quantum computing system according to an embodiment of the present invention. [Figure 2A] These are schematic top view, side view, and cross-sectional view of a quantum transistor according to an embodiment of the present invention. [Figure 2B] These are schematic top view, side view, and cross-sectional view of a quantum transistor according to an embodiment of the present invention. [Figure 2C] These are schematic top view, side view, and cross-sectional view of a quantum transistor according to an embodiment of the present invention. [Figure 3A] This is a schematic cross-sectional view of a semiconductor layer on a diamond crystal in a quantum transistor according to an embodiment of the present invention. [Figure 3B] This is a schematic cross-sectional view of a semiconductor layer on a diamond crystal in a quantum transistor according to an embodiment of the present invention. [Figure 3C] This is a schematic cross-sectional view of a semiconductor layer on a diamond crystal in a quantum transistor according to an embodiment of the present invention. [Figure 4]This plot schematically shows the emission wavelength of the NV color center in a quantum transistor as a function of the voltage applied to the electrodes of the quantum transistor according to an embodiment of the present invention. [Figure 5A] This is a schematic side view of a waveguide in a quantum transistor, showing details of an optical resonator and filter implemented in the waveguide according to an embodiment of the present invention. [Figure 5B] This is a schematic detail diagram of the periodic structure inside the resonator shown in Figure 5A, according to an embodiment of the present invention. [Figure 6] This is a schematic detail diagram of a periodic structure used in a quantum transistor resonator according to another embodiment of the present invention. [Figure 7] This is a schematic cross-sectional view of an optical resonator used in a quantum transistor according to an alternative embodiment of the present invention. [Figure 8] This is a schematic side view of a quantum transistor according to an alternative embodiment of the present invention. [Figure 9] This is a schematic side view of a quantum transistor according to an alternative embodiment of the present invention. [Modes for carrying out the invention]

[0023] overview For the sake of specificity and clarity, the following description will focus on qubits based on NV color centers in diamond. However, these embodiments are described only as examples. The principles of these embodiments can be similarly applied, with necessary modifications, to qubits based on other types of color centers in diamond, as well as on defects in other types of crystals.

[0024] Despite the promising potential and advantages of qubits based on NV defects (and other types of crystal defects) in diamond, practical quantum computing devices based on NV defects have yet to be demonstrated. Experimental systems based on NV defects are still far from meeting the minimum levels of stability, efficiency, and fidelity required for multi-qubit devices. Several problems must be overcome to create a quantum computer based on NV defects.

[0025] Quantum efficiency - NV - The luminescence spectrum of the center comprises a zero-phonon line (ZPL) and a broad phonon sideband containing most of the spontaneous luminescent energy emitted from the excited triplet state. Only the ZPL has the clearly defined frequency and polarization required for qubit manipulation. Non-radiative losses further reduce the quantum efficiency of the ZPL emission.

[0026] Spectral diffusion-NV - The center has an electric dipole moment in both the ground state and the excited state. Therefore, the NV of a qubit is based on it. - The transition frequency is sensitive to local electric fields, which tend to vary with location, causing frequency variations between qubits in multi-qubit devices known as "spread spectrum." For multi-qubit entanglement and other operations, spread spectrum must be kept within tight limits.

[0027] Charge stability - NV centers have two metastable charge states, namely, NV - and NV 0 It has NV using a laser. - Photoexcitation of charged states often leads to ionization, and this results in NV 0 This leads to state transitions and loss of quantum information.

[0028] Embodiments of the present invention described herein address these problems using a novel quantum computing device referred to herein as a “quantum transistor.” Strictly speaking, this device is not a transistor in the sense commonly used in electronic circuits. However, it is referred to herein as a quantum transistor because it is topologically similar to an electronic transistor in that three electrodes are coupled to a solid core.

[0029] In the quantum transistors described herein, crystal defects are contained within an optical resonator having a resonant wavelength band that includes the emission wavelength of the crystal defects (in other words, the ZPL). The resonator may comprise, for example, a periodic structure formed on the opposite side of the defect in a crystalline material (such as diamond). The resonator is designed to have a high Q factor and a low mode volume to provide strong purcell enhancement of spontaneous emission in the ZPL, thereby increasing the quantum efficiency of the device.

[0030] The electrodes, including the source electrode, drain electrode, and gate electrode, are connected to the crystalline material. The source and drain electrodes are positioned on opposite sides of the crystal defect, defining a longitudinal axis through the defect. Applying a voltage between the source and drain electrodes creates an electric field in the crystalline material along the longitudinal axis. Applying a voltage to the gate electrode creates an additional electric field perpendicular to the longitudinal axis. By applying an appropriate voltage between the source and drain electrodes while also applying a voltage to the gate electrode, the control circuit of the quantum transistor can switch the charge state of the crystal defect. This allows, for example, an NV center in diamond to become an NV 0 From the state, the NV required for qubit manipulation - The state is reliably and stably switched to, and NV is maintained throughout the quantum computation. - The NV Center can be maintained in this state.

[0031] Furthermore, by adjusting the voltage applied to the gate electrode, the control circuit can adjust the emission wavelength of the ZPL, thereby canceling out the effects of spectral spread. In this way, multiple qubits can be spectrally calibrated so that their ZPL frequencies are substantially identical, thereby promoting entanglement between qubits and enabling multi-qubit operations.

[0032] In some embodiments, the optical resonator emits a defect at a wavelength (e.g., NV) - The optical waveguide efficiently couples the light emission emitted from the crystal defect (in the red ZPL emission of the defect) to one or more optical waveguides that transmit the light emission from the crystal defect from the optical resonator to the detector. The optical waveguides also efficiently couple one or more excitation beams (e.g., NV) at the appropriate excitation wavelength of the crystal defect. - A green beam (for exciting defects) can be transmitted from one or more beam sources to crystal defects. In some embodiments, the waveguide is formed on a photonic integrated circuit (PIC) substrate on which the defect-containing crystalline material is mounted. Multiple diamond chiplets, each containing an NV defect, can be mounted together on such a PIC, thereby creating a multi-qubit quantum computing device, while the waveguide forms a photonic network that interconnects the qubits for computing operations and output detection purposes.

[0033] System Description Figure 1 is a schematic block diagram showing a quantum computing system 20 according to an embodiment of the present invention. The system 20 comprises an array of quantum transistors 22 mounted on a PIC 24. As shown in detail in subsequent figures, the quantum transistors 22 comprise diamond tiplets, each containing an NV defect contained within an optical resonator, with electrodes connected to the tiplets. In some embodiments, the diamond tiplets comprise waveguides, and the optical resonators are formed in these diamond waveguides coupled to the PIC.

[0034] The PIC24 includes a substrate such as a silicon-on-insulator (SOI) substrate on which a network of waveguides with low propagation loss, such as SiN waveguides, is formed to transmit optical radiation to and from the quantum transistor 22. Alternatively, other types of substrates, such as silicon or glass substrates, may be used. In this example, these waveguides include an input waveguide 28 that injects one or more optical excitation beams, such as a green beam output by a laser 26 at approximately 532 nm, into the quantum transistor 22 via a suitable coupler. In addition, an output waveguide 36 on the PIC24 receives radiation emitted from the quantum transistor at approximately 637 nm, such as NV, via another coupler. - The defect receives red radiation in the ZPL. Methods for optically coupling waveguides 28 and 36 to a diamond tiplet containing an NV defect are described further below.

[0035] In some embodiments, multiple excitation beams are NV - Different wavelengths are applied to excite the defects. In one such embodiment, one excitation beam, such as a green beam at 532 nm, is applied at NV - The second excitation beam is applied at the state transition wavelength, while avoiding ionization of the charged state (in other words, NV 0 (Preventing transition to an charged state) NV defect - The infrared wavelength is applied at a wavelength selected to initialize the charged state. The infrared wavelength is generally selected within the range of 780 to 1900 nm, for example, 1550 nm, and is linearly polarized along a direction perpendicular to the axis of the NV defect structure (in other words, perpendicular to the axis between the nitrogen atom and the crystal vacancy).

[0036] In addition, the microwave source 30 is NV -A microwave input 32 is generated to the quantum transistor 22 to drive transitions between the electron spin energy levels of the ground state. These transitions can be utilized, for example, when reading the state of a qubit using spin conversion to a charge state, as further described below, and when transitioning an NV defect between the ground state and a superposition state, which can be used both in single-qubit operations and when creating entanglement between qubits.

[0037] The electronic control circuit 34 applies electrical signals to the electrodes of the quantum transistor 22 (as shown in subsequent figures) to switch the defect charge state and adjust the emission wavelength of the crystal defects. These functions are further explained below with reference to Figures 3A-3C and Figure 4.

[0038] In the illustrated embodiment, an output waveguide 36 couples a quantum transistor 22 to a photonic network 38, and the photonic network 38 connects the output signals from the quantum transistor to a photodetector 44. In the illustrated example, the photonic network 38 includes an optical switch 40, such as a phase-controlled Mach-Zehnder interferometer. The detector 44 may comprise, for example, a fast avalanche photodiode (APD) or a single-photon avalanche diode (SPAD) fabricated on a separate detector chip 42 optically coupled to the PIC 24. Alternatively, the photodetector may be fabricated on the PIC 24. A fast SPAD with fast quenching may be useful in overcoming spectral spread between quantum transistors. However, details of the network 38 and the detector 44 are outside the scope of this disclosure.

[0039] Optical and electrical structure of quantum transistors Figures 2A, 2B, and 2C are schematic top, side, and cross-sectional views, respectively, of a quantum transistor 22 according to an embodiment of the present invention. In this embodiment, NV defects 54 are formed in a diamond waveguide 52, such as a ridge waveguide in the illustrated embodiment. The NV defects 54 may be formed, for example, by electron irradiation, ion nano-implantation, or pulsed laser irradiation of a diamond crystal. The waveguide 52 in this example comprises a narrow rectangular ridge disposed on a wider slab 50 of diamond. The waveguide and slab may be manufactured, for example, by photolithographic etching of a diamond film. In a typical implementation, the waveguide 52 has a length in the range of 10 to 50 μm, and a height and width in the range of 100 to 300 nm. The thickness of the slab 50 beneath the waveguide 52 is generally in the range of 50 to 150 nm. The dimensions of the waveguide 52 may be advantageously selected to support single-mode operation at both the excitation and emission wavelengths of the defects 54. Alternatively, other dimensions and types of diamond waveguides may be used, such as strips with rectangular (fishbone), triangular, or pentagonal cross-sectional profiles.

[0040] An optical resonator 56 containing the defect 54 is formed in the center of the waveguide 52. The resonator 56 has a high-Q resonant wavelength band that includes the ZPL emission wavelength of the defect 54. The wavelength band of the resonator may be adjustable using a piezoelectric element, for example, as shown in Figure 8. The piezoelectric element may be positioned to the side or below the resonator 56, or it may be formed on the PIC 24. In this embodiment, the resonator 56 is defined by a periodic structure formed in the waveguide 52, for example, as shown in Figures 5A / B, 6 and 7. This type of resonator is advantageous for achieving high Q and small mode volume. Alternatively, other types of resonant structures may be used.

[0041] The input waveguide 28 and output waveguide 36 are terminated at adiabatic tapers 60 and 62, respectively, on the PIC substrate 58 within the quantum transistor 22. Tapers 60 and 62 are fabricated, for example, by suitable etching of the SiN layer on the PIC 24. The tapers 60 and 62 are superimposed with the corresponding inverse tapers of the termination of the diamond waveguide 52 in their respective overlapping regions 61 and 63. Waveguide 52 may be isolated in the Z direction from the underlying tapers 60 and 62 by a thin dielectric layer comprising, for example, SiO2. Green light input through waveguide 28 is adiabatically transferred with low loss by evanescent wave coupling from taper 60 into the overlapping portion of diamond waveguide 52 in region 61, and red light output from defect 54 is similarly transferred from diamond waveguide 52 into taper 62 in region 63. For efficient adiabatic bonding, the lengths of the overlapping regions 61 and 63 in the X direction are generally in the range of 10–20 μm.

[0042] Conductive electrodes, including a source electrode 64, a drain electrode 66, and a gate electrode 68, are deposited on the diamond slab 50 in close proximity to the defect 54. The source electrode 64 and the drain electrode 66 are deposited on opposite sides of the defect 54, defining a longitudinal axis through their respective locations. (In this example, this longitudinal axis runs parallel to the X-axis, but other orientations of the longitudinal axis may be used alternatively.) When a voltage is applied between the source electrode 64 and the drain electrode 66 through an active conductive channel, it generates an electric field in the diamond waveguide 52 along the X-axis. The gate electrode 68 is offset from the longitudinal axis, so that, for example, a voltage applied between the gate electrode and the drain electrode 66 (or between the gate electrode and the source electrode 64) generates a transverse electric field component along the Y-direction in the diamond waveguide 52.

[0043] The control circuit 34 (Figure 1) drives electrodes 64, 66, and 68 to control the charge state of the crystal defect 54 and to tune the ZPL wavelength emitted by the crystal defect. To enable this functionality, a semiconductor donor layer 70 (which may be monolayer or multilayer) is formed on the surface of the diamond waveguide 52 between the electrodes (particularly the gate electrode 68) and the NV defect 54. This donor layer 70 may comprise a transition metal oxide (TMO) and / or transition metal dichalcogenide (TMD), such as MoO3, MoS2, V2O5, WO3, ReO3, CrO3, WS2, or MoSe2. The donor layer 70 may be formed by atomic layer deposition or by other deposition techniques such as thermal deposition, sputtering, or electron beam deposition. The TMO or TMD may be combined with two-dimensional (2D) materials such as graphene, hexagonal boron nitride, or other van der Waals heterostructures. Alternatively, other holdner materials (electron acceptors) may be used, or the donor layer may be formed by suitable doping of the diamond itself. Several possible donor layer configurations are shown as examples in Figures 3A–3C.

[0044] When a suitable voltage is applied to the gate electrode 68, it releases carriers from the donor layer 70 near the defect 54, thereby creating a two-dimensional PIN layer structure on top of the defect, with an undoped intrinsic semiconductor region between the p-type and n-type semiconductor regions. Depending on the electrode configuration, the defect 54 is then NV by switching the polarity of the voltage applied between the source electrode 64 and the drain electrode 66. 0 Charge state and NV - It can be switched between charge states. In other words, applying a sufficient voltage of the appropriate polarity, regardless of the application of the excitation beam from laser 26, can cause the transition of positive and negative carrier bands through the PIN layer structure in the diamond crystal and / or on the diamond surface or interface, thereby NV - This will switch the charge state of defect 54. Applying a voltage of the opposite polarity will result in NV 0The defect 54 will be switched to a different charge state. The polarity and magnitude of the voltages applied to electrodes 64, 66, and 68 for the purpose of switching the charge state depend on the geometric and electrical characteristics of the quantum transistor 22.

[0045] The electric field due to the voltage applied to the gate electrode 68 also changes the ZPL wavelength of the defect 54. Varying the gate voltage over a small range can be used to adjust the ZPL wavelength, for example, in the range of 1-2 nm, as shown in Figure 4. Different voltages can be applied to different quantum transistors 22 in the system 20 to compensate for ZPL variations due to other uncontrolled local electric fields, thereby canceling spectral diffusion between quantum transistors.

[0046] In an alternative embodiment, the charge state and ZPL wavelength of crystal defects such as NV defects 54 can be controlled by applying appropriate voltages between electrodes 64, 66, and 68 without incorporating a donor layer and PIN structure into the quantum transistor. In this case, acoustic-electric interactions and / or Stark interactions can be applied to control the charge state and ZPL wavelength.

[0047] Figure 3A is a schematic cross-sectional view of semiconductor layers superimposed on a diamond crystal in a quantum transistor 22 according to an embodiment of the present invention. The donor layer 70 is deposited on the P-type hydrogen surface termination 71 of the diamond in the resonator 56. The application of a voltage to the gate electrode 68 through the donor layer 70 causes pinning of Fermi energy levels along the heterostructure between carriers in the two-dimensional hole gas (2DHG) 72 in the subsurface diamond, between the donor layer and the defect 54 in the diamond resonator 56, and between carriers formed in the two-dimensional electron gas (2DEG) 74 on the opposite side of the donor layer. The P-type and N-type layers act as acceptors (generating 2DHG in the diamond subsurface) and donors (generating 2DEG). These three layers, namely the P-type electron gas and N-type electron gas and the undoped layer between them, form a two-dimensional PIN structure. The application of a voltage between the source electrode 64 and the drain electrode 66 transfers positive or negative bulk charge from the PIN structure to the diamond bulk, thereby NV 0 State and NV - This will involve switching defect 54 between states, or vice versa.

[0048] Figure 3B is a schematic cross-sectional view of semiconductor layers superimposed on a diamond crystal in a quantum transistor 22 according to another embodiment of the present invention. In this embodiment, a Holdner layer 70 is superimposed on a portion of the diamond in the resonator 56 having a P-type hydrogen surface termination 71. An electron donor layer 80 is superimposed on the adjacent portion of the diamond having an N-type nitrogen surface termination 79. Applying a voltage to the gate electrode 68 results in pinning of the Fermi energy levels between adjacent 2DHG76 and 2DEG78. In other words, the PIN structure in this case is arranged laterally rather than vertically. This structure can be controlled in a manner similar to the structure in Figure 3A to change the charge state of the defect 54 by switching the source-drain voltage.

[0049] Figure 3C is a schematic cross-sectional view of a doped semiconductor layer in diamond superimposed on an undoped diamond crystal in a quantum transistor 22, according to an alternative embodiment of the present invention. In this case, the PIN structure on the defect 54 is created by bulk doping of the diamond subsurface, creating a diamond P-type layer 82 and a diamond N-type layer 84. In other words, the PIN structure is based on a doped multilayer of the diamond itself, acting as acceptor and donor layers. Layers 82 and 84 can be formed, for example, by strongly doping thin layers near the surface of the diamond crystal using boron dopants and phosphorus dopants. The thickness of layers 82 and 84 is generally in the range of 1 to 40 nm. The application of a voltage to the gate electrode 68 will generate a bulk charge in the diamond crystal in a manner similar to that of the embodiment in Figure 3A.

[0050] Figure 4 is a schematic plot showing the emission wavelength of the NV color center in the quantum transistor 22 as a function of the voltage applied to electrodes 64, 66, and 68 of the quantum transistor according to an embodiment of the present invention. The horizontal axis shows the voltage (in volts) applied between the drain electrode 66 and the source electrode 64. When the voltage is positive and is in the region to the left of the dashed vertical line, the defect 54 is NV 0 It remains in a charged state and does not emit radiation in the red transition band. (NV 0 The emission is within a different range of approximately 575 nm. When the drain-source voltage is negative and to the right of the dashed vertical line, defect 54 is NV - It transitions to a charged state.

[0051] In other words, a positive drain-source voltage turns off quantum transistor 22, and a negative drain-source voltage turns on quantum transistor 22, thereby enabling qubit manipulation. Furthermore, continuous application of a negative drain-source voltage results in NV - Maintain the quantum transistor 22 in this state, NV 0 This prevents the transition to a certain state, thereby extending the coherence period during which quantum computation can be performed.

[0052] Each curve 90a, 90b, 90c, ..., 90d shows the relative emission wavelength as a function of the drain-source voltage for different values ​​of the voltage applied between the gate electrode 68 and the source electrode 64. The gate-source voltage is increased in increments of 0.2 volts for each curve, up to a maximum value of 2.8 volts. In the illustrated example, adjusting the gate-source voltage adjusts the ZPL over a range of approximately 420 pm.

[0053] At the end of the quantum computation, the control circuit 34 reads out the spin state of the NV defect 54 in each quantum transistor 22. As mentioned above, one way to read out the spin state is to apply one or more excitation beams to the quantum transistor via the input waveguide 28 at a wavelength selected so that the NV defect 54 outputs an optical signal to the photodetector 44, and measure the optical signal.

[0054] Alternatively, the control circuit 34 may electronically read out the spin state by a spin-charge conversion process. For this purpose, the input waveguide 28 transmits one or more excitation beams to the NV defect 54 at wavelengths selected to convert one or more electronic spin states of the NV defect to their respective charge states. For example, laser beams at green wavelengths and near-infrared wavelengths (such as 532 nm and 1064 nm) can be used to convert the |±1> state without ionizing the NV - |0>Spin states may be preferentially excited and ionized by applying optical excitation. The control circuit 34 detects the charge state of each NV defect by measuring the current between the source electrode 64 and the drain electrode 66. High-intensity optical excitation may be applied to read out the photocurrent from each NV defect with high speed and high signal-to-noise ratio.

[0055] Optical resonators and filters Next, Figures 5A and 5B schematically show the optical structures in waveguides 52, 60, and 62 of the quantum transistor 22 according to embodiments of the present invention. Figure 5A is a side view showing the features of the optical resonator 56 and the filter 98 implemented in waveguide 62. Figure 5B is a detailed view of the periodic structure 94 within the resonator 52.

[0056] The resonator 56 includes periodic structures 94 and 96 formed in the waveguide 52 on the side opposite the defect 54, which act as Bragg reflectors. In this embodiment, these periodic structures include holes 104 extending through the diamond waveguide, as shown in Figure 5B. The holes have a period P selected to reflect light in a band containing the ZPL wavelength. The holes may be filled with air or another material such as SiO2. For example, in the case of a narrow diamond waveguide surrounded by air with air holes, P is NV at 637 nm. - The emission line can be approximately λ / 3 ≈ 212 nm. To maximize the parcel enhancement of ZPL emission, structures 94 and 96 are designed to obtain a high Q, e.g., Q > 2000, in the ZPL band, and the optical mode volume V m To minimize the impact, they are positioned close to each other around defect 54. (Parcel reinforcement is Q / V m (This is proportional to the ratio.) At the same time, as indicated by arrow 102, for efficient collection of radiation emitted from defect 54 into waveguide 62, it is desirable that the periodic structure 94 be entirely reflective, while the structure 96 is only partially reflective.

[0057] One or more excitation beams, for example, a green laser emission at 532 nm, as well as orange, red, or infrared emission, are coupled from waveguide 60 into waveguide 52, as indicated by arrow 100. This green emission passes freely through periodic structures 94 and 96. To prevent the green emission from propagating through output waveguide 36 to detector 44 (Figure 1), an optical filter 98 is formed in waveguide 62. Filter 98 also has a periodic structure, but its period is selected to reflect the green emission back toward overlap region 63.

[0058] Figure 6 is a schematic detail diagram of a periodic structure 106 used in the resonator of a quantum transistor according to another embodiment of the present invention. In this case, the periodic structure 106 includes recesses 108 (creating a "fishbone" structure) that may not pass through the diamond waveguide completely, as in the previous embodiment. This type of periodic structure may be easier to fabricate than structures based on through holes. Structure 106 may be made longer than structure 94 (Figure 5A / B) to compensate for the lower reflectivity of the recesses 108 compared to the holes 104. (This lower reflectivity is a result of lower overlap between the edge recesses and the center-focused mode of the waveguide.)

[0059] Although the holes 104 and recesses 108 have rectangular profiles in Figures 5B and 6, in alternative implementations, the holes and recesses may have other shapes, such as circular or elliptical shapes (not shown in the figures).

[0060] Figure 7 is a schematic cross-sectional view of an optical resonator 110 used in a quantum transistor according to an alternative embodiment of the present invention. To form the resonator 110, a two-dimensional pattern of holes 114 is etched through a diamond crystal 112. One or more of the holes are omitted or modified to define an optical cavity containing defects 54. Light emission from the defects 54 in the ZPL is directed horizontally by reflection from the periodic structure of the holes 114 and vertically by total internal reflection within the diamond crystal 112.

[0061] Alternative Embodiments Figure 8 is a schematic side view of a quantum transistor 120 according to an alternative embodiment of the present invention. The components of quantum transistor 120, which have similar functions to the components of quantum transistor 22 described above, are labeled with the same index number.

[0062] The quantum transistor 120 comprises a diamond chiplet 122 mounted on a PIC 126. The chiplet 122 contains a defect 54 within an optical resonator 124, for example, a Bragg resonator as described above, oriented perpendicular to the PIC 126. Electrodes 64, 66, and 68 are formed on opposing sides of the chiplet 122, and a donor layer (not shown in this figure) lies between one or more of the electrodes 64, 66, and 68 and the bulk of the chiplet 122. The arrangement of the donor layer and semiconductor layer creates a PIN structure in the chiplet 122 as detailed above with reference to Figures 3A-3C. One or more waveguides 128 on the PIC 126 transmit light between an input waveguide 28 and an output waveguide 36. A microwave electrode 130 is used for NV - A microwave source 30 (Figure 1) is connected to generate a signal that manipulates the ground spin state of the charged defect 54.

[0063] A piezoelectric element 132, for example, a suitable layer of piezoelectric crystal, can be actuated by a control circuit 34 (Figure 1) to change the effective length of the optical resonator 124. The control circuit 34 thereby allows tuning of the resonant wavelength of the resonator 124 by applying an appropriate drive voltage to the piezoelectric element 132. This type of piezoelectric resonator tuning allows the control circuit 34 to adjust the ZPL in the range of approximately 1 to 50 nm, thereby compensating for large spectral spread if necessary.

[0064] Figure 9 is a schematic side view of a quantum transistor 140 according to yet another embodiment of the present invention. The quantum transistor 140 is similar in design to the quantum transistor 120 (Figure 8), with a reflective surface 144 added on the PIC 142 to couple light emission between the diamond tiplet 122 and one or more optical waveguides 146 on the PIC 142. The reflective surface 144 may be etched into the PIC substrate at a 45-degree angle and coated for high reflectivity. This type of coupling may be more efficient than the adiabatic tapered base coupler described previously.

[0065] The embodiments described above are illustrative examples, and the present invention is not limited to those described in detail above. Rather, the scope of the present invention includes both combinations and partial combinations of the various features described above, as well as variations and modifications thereof not disclosed in the prior art, which would be conceivable to those skilled in the art by reading the above description.

Claims

1. An optical resonator having a resonant wavelength band, A crystalline material comprising crystal defects contained within the optical resonator, wherein the crystal defects have a ground state and an excited state having an emission wavelength within the resonant wavelength band, A source electrode and a drain electrode are disposed on the side opposite to the crystal defect and configured to apply a first electric field to the crystal material along the longitudinal axis, A gate electrode is disposed in close proximity to the crystal defect and configured to apply a second electric field perpendicular to the longitudinal axis to the crystal material, A control circuit is configured to apply a first voltage between the source electrode and the drain electrode to control the charge state of the crystal defect, and to apply a second voltage to the gate electrode to adjust the emission wavelength. A quantum computing device equipped with [the following features].

2. The device according to claim 1, wherein the crystalline material comprises diamond.

3. The device according to claim 2, wherein the crystal defects include nitrogen vacancy (NV) defects.

4. The application of the first voltage between the source electrode and the drain electrode is NV 0 Status and NV - The device according to claim 3, which switches between the NV defect state and the state.

5. The device according to claim 1, wherein the application of a first electric field having a first polarity switches the crystal defect to a first charge state, and the application of a first electric field having a second polarity opposite to the first polarity switches the crystal defect to a second charge state having the ground state and the excited state having the emission wavelength in the resonant wavelength band.

6. The device according to claim 5, wherein the control circuit is configured to apply the first voltage in order to maintain the crystal defect in the second charge state during the quantum computation period.

7. The device according to claim 5, comprising an optical waveguide configured to transmit one or more excitation beams to the crystal defect at wavelengths selected to convert one or more electron spin states of the crystal defect into their respective charge states, wherein the controller is configured to detect the charge state of the crystal defect by measuring the current between the source electrode and the drain electrode.

8. The device according to claim 5, comprising an optical waveguide configured to transmit one or more excitation beams to the crystal defect, the first excitation beam being at the transition wavelength of the second charge state, and the second excitation beam being at an infrared wavelength selected to initialize the crystal defect in the second charge state while preventing the conversion of the second charge state to the first charge state.

9. The device according to claim 1, wherein the control circuit is configured to adjust the second voltage in order to adjust the emission wavelength of the crystal defect.

10. The device according to any one of claims 1 to 9, comprising a semiconductor donor layer disposed between at least one of the electrodes and the crystal defect.

11. The device according to claim 10, wherein the application of the second electric field creates a two-dimensional PIN structure on the crystal defect.

12. The device according to claim 10, wherein the semiconductor donor layer comprises one or more transition metal oxides (TMOs) and transition metal dichalcogenides (TMDs).

13. The device according to any one of claims 1 to 9, comprising a piezoelectric element coupled to change the length of the optical resonator, wherein the control circuit is configured to drive the piezoelectric element to adjust the resonant wavelength band of the optical resonator.

14. The device according to any one of claims 1 to 9, wherein the optical resonator comprises a periodic structure formed in the crystalline material on the side opposite to the crystal defect.

15. The device according to claim 14, wherein the periodic structure comprises holes extending through a layer of the crystalline material containing the crystal defects.

16. The device according to claim 14, wherein the periodic structure comprises depressions on the surface of the crystalline material.

17. The device according to any one of claims 1 to 9, wherein the crystalline material is configured as an optical waveguide coupled to transmit light radiation emitted from the crystal defects at the emission wavelength from the optical resonator to the detector.

18. The device according to claim 17, wherein the optical waveguide is further coupled to transmit one or more excitation beams at one or more excitation wavelengths from one or more beam sources to the crystal defect.

19. The optical waveguide is disposed on a substrate thereon, An input waveguide disposed on the substrate and coupled to the optical waveguide for injecting one or more excitation beams, An output waveguide disposed on the substrate and coupled to receive the light radiation emitted from the optical waveguide, The device according to claim 18, comprising:

20. The device according to claim 19, wherein the optical waveguide, the input waveguide, and the output waveguide each have tapered ends, the tapered ends being superimposed on the substrate to inject one or more excitation beams into the optical waveguide and inject the emitted light radiation into the output waveguide by adiabatic coupling.

21. The device according to claim 19, wherein the output waveguide comprises a filter configured to block the excitation wavelength.

22. The device according to claim 17, wherein the optical waveguide comprises a ridge disposed on a slab of the crystalline material.

23. The device according to claim 17, wherein the optical waveguide has a cross-sectional profile selected from a group of profiles consisting of rectangular profiles, triangular profiles, and pentagonal profiles.

24. A photonic integrated circuit (PIC) substrate on which the aforementioned crystalline material is disposed, One or more optical waveguides disposed on the substrate and optically coupled to the crystalline material A device according to any one of claims 1 to 9, comprising:

25. The device according to claim 24, wherein the one or more optical waveguides comprises at least one inverse taper configured to couple light radiation between the crystalline material and the one or more optical waveguides.

26. The device according to claim 24, wherein the PIC comprises a reflective surface configured to couple light emission between the crystalline material and one or more optical waveguides.

27. To provide a crystalline material having crystal defects in an optical resonator, wherein the crystal defects have a ground state and an excited state having an emission wavelength within the resonant wavelength band of the optical resonator, In order to apply a first electric field to the crystalline material along the longitudinal axis, the source electrode and drain electrode are positioned on the side opposite the crystal defect, In order to apply a second electric field perpendicular to the longitudinal axis to the crystalline material, the gate electrode is positioned close to the crystal defect, To control the charge state of the crystal defect, a first voltage is applied between the source electrode and the drain electrode, and to adjust the emission wavelength, a second voltage is applied to the gate electrode. Methods for quantum computing, including those mentioned above.

28. The method according to claim 27, wherein the crystalline material comprises diamond.

29. The method according to claim 28, wherein the crystal defects include nitrogen vacancy (NV) defects.

30. Applying the first voltage between the source electrode and the drain electrode is NV 0 Status and NV - The method according to claim 29, which involves switching between the NV defect and the state.

31. The method according to claim 27, wherein applying a first voltage having a first polarity switches the crystal defect to a first charge state, and applying a first voltage having a second polarity opposite to the first polarity switches the crystal defect to a second charge state having the ground state and the excited state having the emission wavelength in the resonant wavelength band.

32. The method according to claim 31, wherein the first voltage is applied to maintain the crystal defect in the second charge state during the quantum computation.

33. The method according to claim 31, comprising: transmitting one or more excitation beams to the crystal defect at a wavelength selected to convert one or more electron spin states of the crystal defect into their respective charge states; and detecting the charge state of the crystal defect by measuring the current between the source electrode and the drain electrode.

34. The method according to claim 31, comprising transmitting one or more excitation beams to the crystal defect, the first excitation beam being at the transition wavelength of the second charge state, and the second excitation beam being at an infrared wavelength selected to initialize the crystal defect in the second charge state while preventing the conversion of the second charge state to the first charge state.

35. The method according to claim 27, wherein applying the second voltage includes adjusting the second voltage to adjust the emission wavelength of the crystal defect.

36. The method according to any one of claims 27 to 35, comprising forming a semiconductor donor layer between at least one of the electrodes and the crystal defect.

37. The method according to claim 36, wherein the application of the second electric field creates a two-dimensional PIN structure on the crystal defect.

38. The method according to claim 29, wherein the semiconductor donor layer comprises one or more transition metal oxides (TMOs) and transition metal dichalcogenides (TMDs).

39. The method according to any one of claims 27 to 35, comprising coupling a piezoelectric element to change the length of the optical resonator and driving the piezoelectric element to adjust the resonant wavelength band of the optical resonator.

40. The method according to any one of claims 27 to 35, wherein providing the crystalline material comprises forming a periodic structure in the crystalline material on the side opposite to the crystal defect in order to define the optical resonator.

41. The method according to claim 40, wherein forming the periodic structure includes forming a pore extending through a layer of the crystalline material containing the crystal defects.

42. The method according to claim 40, wherein forming the periodic structure includes forming depressions on the surface of the crystalline material.

43. The method according to any one of claims 27 to 35, wherein the crystalline material is configured as an optical waveguide, and the method includes coupling the optical waveguide to transmit light radiation emitted from the crystal defect at the emission wavelength from the optical resonator to a detector.

44. The method according to claim 43, further comprising coupling the optical waveguide to transmit one or more excitation beams at one or more excitation wavelengths from one or more beam sources to the crystal defect.

45. The method according to claim 44, comprising arranging the optical waveguide on a substrate, wherein coupling the optical waveguide includes coupling an input waveguide on the substrate to inject one or more excitation beams into the optical waveguide and coupling an output waveguide on the substrate to receive the light radiation emitted from the optical waveguide.

46. The method according to claim 45, wherein the optical waveguide, the input waveguide, and the output waveguide each have tapered ends, the tapered ends being superimposed on the substrate to inject the one or more excitation beams into the optical waveguide and inject the emitted light radiation into the output waveguide by adiabatic coupling.

47. The method according to claim 45, wherein coupling the output waveguide includes providing a filter to block the excitation wavelength from propagating through the output waveguide.

48. The method according to claim 43, wherein the optical waveguide comprises a ridge disposed on a slab of the crystalline material.

49. The method according to claim 43, wherein the optical waveguide has a cross-sectional profile selected from a group of profiles consisting of rectangular profiles, triangular profiles, and pentagonal profiles.

50. The method according to any one of claims 27 to 35, wherein providing the crystalline material includes arranging the crystalline material on a photonic integrated circuit (PIC) substrate and optically coupling one or more optical waveguides on the substrate to the crystalline material.

51. The method according to claim 50, wherein optically coupling the one or more optical waveguides includes coupling light radiation between the crystalline material and the one or more optical waveguides via at least one inverse taper in the one or more optical waveguides.

52. The method according to claim 50, wherein optically coupling the one or more optical waveguides includes providing a reflective surface on the PIC for coupling light radiation between the crystalline material and the one or more optical waveguides.

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