Device and method for electrical readout of point defect spins

Abstract

A quantum information processing device is disclosed. The quantum information processing device comprises a semiconductor device and a single-electron electrometer electrically connected to the semiconductor device. The semiconductor device comprises a plurality of point defects having a plurality of quantum states associated with at least one electron. First transitions are effectible between first ones of the plurality of quantum states by means of electromagnetic signals interacting with the at least one electron. Second transitions occur between second ones of the plurality of states. At least some of the plurality of point defects are arranged in the semiconductor device at distances below 20 nm. The single-electron electrometer is configured to be operated at frequencies of 1 MHz or more.

Description

DescriptionTitle: Device and method for electrical readout of point defect spinsTechnical field

[0001] The present disclosure belongs to the fields of the quantum information processing and quantum computing.

[0002] The present disclosure relates to a device and a method for electrical readout of electronic spins associated with point defects in a semiconductor device.Background of the disclosure

[0003] The quantum physics of diamond-based nitrogen-vacancy centers (NV-centers) has led to diamond devices enabling sensing at room temperature by means of electron spins located at the NV-centers. For example, magnetic fields can be measured at room temperature with high accuracy and high resolution by means of the diamond devices.

[0004] Developing an integrated quantum chip capable of quantum information processing for executing digital quantum computing operations based on point defects in a semiconductor material, like the NV-centers in diamond, requires a scalable physical hardware platform, including a scalable quantum system with reliable qubits. Reliable qubits require the ability to perform qubit-specific quantum operations, e.g., initialization, control, and readout, with a high fidelity and at fast timescales. The integrated chip further requires control and readout structures.

[0005] A number of prior art documents are known that teach control and readout structures for quantum information processing. For example, US 2022 / 318661 Al discloses a method of addressing at least one qubit to be addressed in a set of two or more qubits. The method includes exposing the qubit to be addressed to an electromagnetic field, and at a same time exposing another qubit of the set of two or more qubits to an electromagnetic counter field in such a way that the electromagnetic field has no effect on the other qubit or that the electromagnetic field has a different effect on the other qubit than on the qubit to be addressed. A device for performing the method includes the set of two or more qubits and electromagnetic sources for generating the electromagnetic field and electromagnetic counter field.

[0006] EP 1 669 911 A2 discloses a control system for an array of qubits. The control system provides currents and voltages to qubits in the array of qubits in order to perform functions on the qubit. The functions that the control system can perform include readout, initialization, and entanglement. The state of a qubit can be determined by grounding the qubit, applying a current across the qubit, measuring the resulting potential drop across the qubit, and interpreting the potential drop as a state of the qubit. A qubit can be initialized by grounding the qubit and applying a current across the qubit in a selected direction for a time sufficient that the quantum state of the qubit can relax into the selected state. The qubit can be initialized by grounding the qubit and applying a current across the qubit in a selected direction and then ramping the current to zero in order that the state of the qubit relaxes into the selected state. The states of two qubits can be entangled by coupling the two qubits through a switch. The switch that is capable of grounding the qubits can also be utilized for entangling selected qubits.

[0007] Ishihara et al., "3D Integration Technology for Quantum Computer based on Diamond Spin Qubits", 2021 IEEE International Electron Devices Meeting (IEDM), 11 December 2021, provides a review of trends of the integration technology for implementation of a scalable quantum computer based on diamond spin qubits.Summary of the disclosure

[0008] The present disclosure relates to a device and a method for electric readout of spin states of electrons of NV-centers.

[0009] A quantum information processing device is disclosed. The quantum information processing device comprises a semiconductor device, a plurality of electrodes provided on at least one surface of the semiconductor device, and at least one single-electron electrometer electrically connected to the semiconductor device by the plurality of electrodes. The semiconductor device comprises a plurality of point defects having a plurality of quantum states associated with at least one electron. First transitions are effectible between first ones of the plurality of quantum states by means of electromagnetic signals interacting with the at least one electron. Second transitions occur between second ones of the plurality of states. At least some of the plurality of point defects are arranged in the semiconductor device at defect distances below 20 nm. The at least one single-electron electrometer is configured to be operated at frequencies of 1 MHz or more.

[0010] The quantum information processing device of this document enables an operating regime at room temperature. The quantum information processing device is capable of high-speed (MHz) high-fidelity (registration of individual features of individual electrons) quantum information processing.

[0011] The quantum information processing device enables electrical readout of an electronic spin state associated with a selected one of the plurality of point defects.

[0012] The at least one single-electron electrometer may comprise an amplifier configured to be operated at frequencies of 1 MHz or more.

[0013] The amplifier may comprise at least one of a single-electron transistor or a bipolar transistor.

[0014] The quantum information processing device may further comprise an electromagnetic source for generating the electromagnetic signals.

[0015] The electromagnetic source may be an optical source, and the electromagnetic signals may be optical signals.

[0016] The semiconductor device may further comprise impurities.

[0017] The impurities may comprise electron donors and / or electron acceptors.

[0018] The plurality of point defects may form a two-dimensional array or a three- dimensional array and, in one aspect, the point defects may form a linear chain.

[0019] At least some of the point defects of the plurality of point defects may be arranged in the semiconductor device at defect distances, i.e. distances between the point defects, below 10 nm.

[0020] The semiconductor device may comprise diamond.

[0021] At least some of the point defects may be nitrogen-vacancy centers.

[0022] The plurality of electrodes may be arranged in pairs, and the quantum information processing device may comprise, for at least some of the electrodes, a single one of the single-electron electrometer per electrode pair.

[0023] The plurality of electrodes may be arranged in pairs, and the quantum information processing device may comprise, for at least some of the electrodes, a single one of the single-electron electrometer per several electrode pairs.

[0024] A method of manufacturing a quantum information processing device is disclosed. The method comprises the steps of providing a semiconductor device. The method further comprises a step of fabricating a plurality of point defects, having a plurality of quantum states associated with at least one electron. First transitions are effectible between first ones of the plurality of quantum states by means of electromagnetic signals interacting with the at least one electron. Second transitions occur between second ones of the plurality of states. At least some of the plurality of point defects are arranged in the semiconductor device at defect distances below 20 nm. The method further comprises the step of arranging a plurality of electrodes on at least one surface of the semiconductor device. The method further comprises the step of electrically connecting the semiconductor device with at least one single-electron electrometer via the plurality of electrodes, wherein the at least one single-electron electrometer is configured to be operated at frequencies of 1MHz or more.

[0025] The method may further comprise providing an electromagnetic source for generating electromagnetic signals configured to interact with the plurality of point defects.

[0026] The providing of an electromagnetic source may comprise providing an optical source.

[0027] The method may further comprise introducing impurities to the semiconductor device.

[0028] The method may further comprise arranging the semiconductor device on a chip.

[0029] The method may further comprise arranging the electromagnetic source on the chip.Brief description of the drawings

[0030] FIG. 1 is a schematic of quantum states of a NV-center in a semiconductor device made of diamond.

[0031] FIG. 2 is a schematic of a linear chain of NV-centers in diamond.

[0032] FIG. 3 is a schematic of a two-dimensional arrangement of NV-centers in diamond.

[0033] FIG. 4 is a schematic of an irregular arrangement of NV-centers in diamond.

[0034] FIG. 5 shows the relationship between defect distances and the coupling strength.

[0035] FIGS. 6A-6F show simulation results for a photocurrent and a photoluminescence of an NV-center resulting from excitation by means of an electromagnetic driving signal.

[0036] FIG. 7 shows a quantum information processing device.

[0037] FIG. 8 shows a method of manufacturing a quantum information processing device.Detailed description

[0038] The present disclosure relates to a quantum information processing device 10 comprising a semiconductor device 15, the semiconductor device 15 comprising a plurality of point defects 20 arranged in the semiconductor device 15. The quantum information processing device 10 enables electrical readout of an electronic spin state associated with a selected one of the plurality of point defects 20.

[0039] The semiconductor device 15 is made from a semiconducting material. Examples of the semiconducting material are diamond or silicon carbide. The semiconductor device 15 may comprise dopants 23, such as electron donors and / or electron acceptors. The dopants 23 enable altering an electrical conductivity of the semiconductor device 15. The dopants 23 further enable altering a bandgap of the semiconductor device 15.

[0040] The dopants 23 may comprise Carbon-13 (also referred to as13C).

[0041] A point defect of the plurality of point defects 20 is a crystalline defect at a lattice point of a crystalline lattice. The point defect 20 is known to have atom-like properties. An example of the atom-like properties are electronic states of the point defect 20, defined, for instance, by an orbital, an angular momentum, and / or an electronic spin. Another example of the atom-like properties are interactions between the orbital, the electronic spin, nuclear spins, phonons, and external fields.

[0042] Furthermore, the point defect 20 may have one or more electric charge states corresponding to different electrical charge values of the point defect 20.

[0043] An example of the point defect 20 is a NV-center (nitrogen-vacancy center) in diamond. The NV-center is a magnetically dipolar coupled nitrogen vacancy.

[0044] The NV-center comprises a vacancy in the diamond lattice and a nitrogen atom at one of the nearest-neighbour lattice points. The NV-center in a diamond lattice enables room-temperature quantum information processing.A further example of the point defect 20 is a silicon vacancy (SiV) in diamond. Other examples of the point defect 20 include, but are not limited to, a silicon vacancy (SiV) or a carbon vacancy in silicon carbide. However, such point defects 20 do not enable room temperature quantum information processing.

[0045] The NV-center has a neutral electric charge state NV°, in which the electric charge value of the NV-center is 0 (neutrally charged NV-center). The NV-center furthermore has a negative electric charge state NV , in which the electric charge value of the NV-center is — le = — 1.6 x 10-19C (negatively charged NV-center).

[0046] FIG. 1 shows a system relating to the NV-center in diamond. The system comprises a plurality of quantum states as well as a plurality of transitions among the plurality of quantum states. The plurality of transitions enables a control of the system by means of one or more electromagnetic driving signals to alter occupancies associated with the plurality of quantum states. The occupancies may be altered such that the NV-center is initialised to an initialisation state, e.g., to the state3A2 with electronic spin state |0 >.

[0047] When the NV-center is initialised to the initialisation state having a defined electron spin state, the NV-center is also said to be polarised. One way of achieving the initialisation state (or polarised state) is to alter the occupancies of the plurality of quantum states by driving the NV-center by means of exposure to the electromagnetic driving signals, e.g., to optical radiation. In one aspect of the disclosure, by initialising the NV-center the nuclear spins may be initialised. The nuclear spins may be initialised based on interactions of the electronic spins and the nuclear spins, such as hyperfine interactions.

[0048] The transitions further enable a readout of at least one current one of the plurality of quantum states (referred to as the current state). The current state may depend on one or more of the nuclear spins in a vicinity of the NV-center.

[0049] The readout of the nuclear-spin dependent current state enables readout of the one or more of the nuclear spins. Such readout enables the quantum information processing device 10 to be used for a quantum computer. In one aspect, the electronic states may be used for initialisation or readout of the current state, and the nuclear spin states may be used as qubits for the quantum computer (see also below).

[0050] Qubits for quantum information processing are formed by the nuclear spins of each NV-center.

[0051] A laser 50 may be used for writing and reading the qubits.

[0052] FIG. 1 shows the plurality of quantum states of the NV-center in diamond. The plurality of quantum states is associated with electronic states and with the charge states NV° and NV of the NV-center in diamond. The charge states NV° and NV are indicated by the dashed rectangles in FIG. 1. The electronic states are indicated in FIG. 1 by bold horizontal lines.

[0053] For the neutral charge state NV°, the electronic states include the doublet states2A2 and2E as well as the metastable state4A2.

[0054] For the negative charge state NV , the electronic states include the excited triplet state3E, the triplet ground state3A2, and one or more metastable singlet states MS.

[0055] FIG. 1 furthermore shows the plurality of transitions among the plurality of quantum states of the NV-center. The arrows shown in FIG. 1 represent ones of the plurality of transitions among the electronic states and / or among transitions the charge states. The plurality of transitions is associated with an initial state and a final state from the plurality of quantum states. The plurality of transitions is associated with an energy difference Etransbetween the initial state and the final state. When one of the plurality of transitions occurs, an electron occupying the corresponding initial state transitions, or is transferred, to the corresponding final state. The plurality of transitions is associated with a transition rate, e.g., one of the transition rates X, R, Ro, shown FIG. 1. Some of the transitions are associated with a photon absorption cross-section oy, the multiplication of which by a power of an electromagnetic driving signal (see below), e.g., X or I in FIG. 1, results in the corresponding transition rate. The transition rates may be in a range of approximately 1 to 100 MHz (see,e.g., Gulka et al. (2021) or Razinkovas et al. (2021)). The range of 1 to 100 MHz corresponds to a time scale for the transition rate of 0.01 ps to 1 ps.

[0056] The single-electron electrometer 40 is configured to capture electron transitions with high temporal resolution, i.e. electron transitions occurring on a time scale of 1 ps or even faster.

[0057] Therefore, the single-electron electrometer 40 is configured to be operated at frequencies of 1 MHz or more.

[0058] The cross-sections may be in a range of approximately 1 to 100 MHz / mW (see, e.g., Gulka et al. (2021) or Razinkovas et al. (2021)). The transition rates and the crosssections may be determined experimentally and / or by parameter estimation based on fitting a model (see below).

[0059] The transitions rates in FIG. 1 that are not associated with a change of the charge state include the optical excitation rate X; the radiative decay rates R and Ro, the upper inter- system-crossing (ISC) rates U±+ <J3X and Uo+ <J3X, that include spin-dependent terms U±, Uoand a wavelength-dependent and charge dynamics-related scaling term <J3X; the lower inter-system-crossing spin-dependent rates L±and Lo; and the optical excitation rate a X of the transition of the neutrally charged NV-center.

[0060] The transitions rates in FIG. 1 that are associated with a change of the charge state include the ionization rate <J4X from the excited triplet state3E of the NV' to the metastable4A2 state of the NV°, the recombination rate <J5X from the metastable4A2 electronic state of the NV° to the triplet ground state of the NV', the combined ionization rate I + <J2A from both singlet states of the NV' to the2E state of the NV°, and the recombination rate <J6X from the2A2 electronic state of the NV° to the lower singlet state of the NV'.

[0061] Upward-pointing continuous arrows indicate energy-increasing transitions to an electronic state of higher energy. The energy -increasing transitions occur upon an interaction between an electron, occupying the corresponding initial state, and an electromagnetic driving signal generated by means of an electromagnetic source or illumination laser 50, e.g., during pumping. A photon of the electromagnetic driving signal interacts with an electron, occupying the corresponding initial state. The interaction of the photon with the electronresults in the energy-increasing transition. The illumination laser 50 may generate one of the electromagnetic driving signals having a wavelength in the optical range.

[0062] When the electromagnetic driving signal has a wavelengthexcin an excitation wavelength range corresponding to the energy difference between the initial state and the final state of the corresponding energy-increasing transition, the interaction between the photon of the electromagnetic signal and an electron occupying the initial state may be more likely to result in this transition. The photon of the electromagnetic signal, which has a wavelength in the excitation wavelength range, has an energy equal to, or in a range about, the energy difference Etransof the corresponding transition (i.e., Ephoto= h c / exc« Etrans, where h is Planck’s constant and c is the speed of light). In this way, each energyincreasing transitions is associated with a corresponding excitation wavelength range, in which a probability of this energy-increasing transition occurring is increased.

[0063] Downward-pointing dotted arrows indicate energy-decreasing transitions to an electronic state of lower energy. The energy-decreasing transitions occur spontaneously. Furthermore, the energy-decreasing transitions may be stimulated, e.g., by electromagnetic signal.

[0064] When one of the energy-decreasing transitions occurs, a photon is emitted by an electron transitioning from the corresponding initial state to the corresponding final state. This emission of a photon is referred to as photoluminescence. The photoluminescence photon has a wavelength substantially equal to the energy difference EEtransof the corresponding energy-decreasing transition. The photoluminescence enables readout of the current state of the NV-center.

[0065] Upon exposing the NV-center to the electromagnetic driving signal, occupancies associated with the plurality of quantum states (i.e., probabilities, associated with the plurality of quantum states, of an electron occupying the corresponding quantum state) change. Based on a quantum mechanical model, a time evolution of the occupancies associated with the plurality of quantum states can be calculated or simulated (see below).

[0066] The calculated or simulated time evolution of the occupancies associated with the plurality of quantum states results in sequences of transitions of one or more electrons amongthe plurality of quantum states. The sequences of transitions lead to experimentally detectable signals.

[0067] When the sequence of transitions results in a change of the charge state of the NV- center, i.e., from the negative charge state NV to the neutral charge state NV° or from the neutral charge state NV° to the negative charge state NV , an electron is removed from the systems or added to the system, respectively.

[0068] When an electron is removed from the negatively charged NV-center NV , the electron may be transferred to a conduction band of the semiconductor device 15. The removal of the electron from the NV-center occurs by a single-photon or two-photon ionization process. In the single-photon ionization process, an electron is photoelectrically transferred from the state3A2 to the conduction band. An experimentally determined photon energy for the single-photon process is approximately 2.6 to 2.7 eV. In the two-photon ionization process, in which excitation of an electron to an excited state, e.g., to the state3E, and subsequent photoelectrical transferal of the excited electron from the excited state, e.g., from the state3E to the conduction band occur. An efficiency of the two-photon ionization may be enhanced by increasing the power of the electromagnetic driving signal.

[0069] In the conduction band, the electron, photoelectrically transferred to the conduction band, may be shuttled or moved in the conduction band by applying an electric field (or voltage). For example, the photoelectrically transferred electron may be moved by an electric field to a single-electron electrometer 40.

[0070] In one aspect, the single-electron electrometer is configured to count individual electrons.

[0071] In another aspect, the single-electron electrometer comprises additionally an amplifier. The amplifier may be, but is not limited to, a single-electron transistor, a single electron bipolar avalanche transistor (SEBAT) or a transimpedance amplifier, but this is not limiting of the invention.

[0072] The amplifier is configured to measure a signal, such as a current (i.e. electrons), and amplify the signal, i.e. increase a signal strength of the signal.

[0073] The signal may be converted before being amplified. For example, if the measured signal is a current, the current may be converted into voltage and the voltage may then be amplified.

[0074] The amplifier is configured to be operated at frequencies of 1 MHz or more.

[0075] The shuttling or movement of the photoelectrically transferred electron to the single-electron electrometer 40 enables detecting the photoelectrically transferred electron at the single-electron electrometer 40. Detecting a plurality of the photoelectrically transferred electron at the single-electron electrometer 40 for a detection period enables measuring an electron current (current of transferred electrons) at the single-electron electrometer 40 for the detection period. The electron current contributes to a measured current measured by the single-electron electrometer 40. When the measured current is driven by the two-photon ionization process, the measured current is referred to as photocurrent.

[0076] One or more single-electron electrometers 40 may be used.

[0077] When an electron is added to the neutrally charged NV-center NV°, the electron may be transferred from a valence band of the semiconductor device 15 to the NV-center. One possible mechanism for the adding of an electron to the NV-center is electron capture ionization. When an electron from the valence band is added to the NV-center, a hole is generated in the valence band. The generated hole may contribute to the photocurrent measured at the single-electron electrometer 40. More generally, a plurality of the holes may generate a hole current. The hole current generated during the detection period may contribute to the measured current measured by the single-electron electrometer 40. For example, the hole current may contribute to the photocurrent. For example, the electron current and the hole current may each add to the photocurrent.

[0078] FIG. 2 and FIG. 3 show different arrangements of the point defects 20 in coupling space. A representation in coupling space allows illustration of the coupling, i.e. interaction, between ones of the point defects 20. It will be appreciated that this is only a virtual representation. In one aspect, the representation of point defects 20 in coupling space may correspond to an actual arrangement of the point defects (i.e. actual positions of point defectsin the semiconductor device 15, and actual defect distances between point defects 20 in real three-dimensional space.

[0079] In another aspect, the representation of point defects 20 in coupling space may not correspond to an actual arrangement of the point defects 20 in real three-dimensional space.

[0080] The point defects 20 are coupled by a spin-spin interaction between the electronic spins of point defects 20.

[0081] As noted above, the point defects 20 may form a linear chain. For example, the chain can be a linear chain of point defects 20 as shown in FIG. 2. In the linear chain of point defects 20, each point defect 20 is coupled to two other ones of the point effects 20 (except for the point defects 20 located at both ends of the linear chain).

[0082] In another aspect (not shown in the figures), the linear chain may form a closed loop. In the closed loop, each point defect 20 is coupled to two other, neighbouring ones of the point effects 20.

[0083] FIG. 3 shows a two-dimensional array of point defects 20. In this example, the point defects 20 are coupled to eight other, neighbouring ones of the point defects 20 (except, of course, at the edges of the two-dimensional array).

[0084] In one aspect, an actual arrangement (i.e. an arrangement in real three-dimensional space) of the point defects 20 may be a regular arrangement (as the arrangement shown in FIG. 3).

[0085] In another aspect shown in FIG. 4, an actual arrangement of the point defects 20 may be an irregular arrangement.

[0086] In FIG. 3, the array of points defects 20 or the linear chain of point defects 20 may be arranged at a distance to a surface of a semiconductor device 15 (described below). The distance enables electrical and electromagnetic control of a single one of the plurality of point defects 20. The array may be arranged close to the surface of the semiconductor device 15, on which electrodes (i.e. metallic contacts) are arranged.

[0087] The electrodes may be placed on the surface of the semiconductor device 15 by a fabrication process, such as but not limited to a lift-off process or a metal deposition process.

[0088] The single-electron electrometer 40 may be connected to the electrodes using different interconnecting techniques, such as, but not limited to, wire bonding, flip chip bonding, ball grid arrays or hybrid bonding.

[0089] The distance of the array or the linear chain from the surface may be chosen to increase the probability of detecting an electron transferred from the plurality of point defects 20 to a conduction band of the semiconductor device 15. The arrangement the plurality of NV-centers in the array or the linear chain means that any one of the plurality of NV-centers has at least one neighbouring one of the plurality of NV-centers. In one aspect of the disclosure, the defect distances (i.e. distances between the point defects 20) between ones of the plurality of point defects 20 and the corresponding at least one neighbouring one of the point defects 20 (nearest-neighbour distance of the array or the linear chain) is less than 20 nm. In a further aspect, the defect distances are less than or equal to 10 nm. In yet a further aspect, the defect distances are less than or equal to 5 nm.

[0090] The plurality of point defects 20 arranged in the array shown in FIG. 3 or / the linear chain shown in FIG. 2 are coupled by a spin-spin interaction between the electronic spins at the plurality of point defects 20.

[0091] It will be appreciated that there are many possible arrangements of point defects 20 in the semiconductor device 15.

[0092] In one aspect, an arrangement of the point defects 20 in the semiconductor device 15 may be determined by constraints regarding fabrication of the point defects 20 in the semiconductor device 15.

[0093] In another aspect, an arrangement of the points defects 20 in the semiconductor device 15 may be determined according to an intended application of the quantum information processing device 10.

[0094] For example, an intended application of the quantum information processing device 10 may be an execution of a quantum circuit on the quantum information processing device 10. The point defects 20 within the semiconductor device 15 (which form the qubits) of the quantum information processing device 10 may then be arranged in order to provide an adapted topology for the execution of the quantum circuit.

[0095] An optimized arrangement may be determined by optimizing a figure of merit. In one aspect, the figure of merit may be defined as a product of a coupling strength between point defects 20 and a coherence time of the point defects 20: FM = J x T2, where FM is the figure of merit, J is the coupling strength and T2 is the coherence time.

[0096] The coupling strength J between points defects 20 follows the inverse 3rdpower law, i.e., 1 / r3, where r is the defect distance.

[0097] The spin-spin interaction (magnetic dipole-dipole interaction) between point defects 20 follows the inverse 3rdpower law, i.e., 1 / r3, where r is the defect distance between the interacting electronic spins.

[0098] The spin-spin interaction decreases rapidly when the defect distance between interacting ones of the plurality of point defects 20 increases. The defect distances being «20nm enables the coupling strengths (in terms of frequency » kHz) between the plurality of point defects 20 that ensure high-fidelity high-speed quantum operations of initialization, control, and readout.

[0099] During manufacturing of the semiconductor device 15, the fabrication of the plurality of point defects 20 is controllable such that the defect distances lie in a predetermined range. In one example, this predetermined range of the defect distances between the plurality of point defects 20 comprises values smaller than or equal to 20 nm.

[0100] The point defects 20 may be created in the semiconductor device 15 by molecular implantation.

[0101] For room -temperature high-speed high-fidelity digital quantum information processing, the NV-centers are strongly coupled to each other. This coupling is achieved through magnetic dipolar interactions. In one aspect, the NV-centers are within defect distances below 20nm from each other. FIG. 5 shows the relationship between the defect distances and the coupling strength J.

[0102] In another non-limiting example, this range comprises values smaller than or equal to 10 nm. In a further non-limiting example, this range comprises values of about 5 nm, such as values larger than or equal to 3 nm and smaller than or equal to 7 nm, or values larger than or equal to 4 nm and smaller than or equal to 6 nm.

[0103] Controlling the defect distance of the plurality of point defects 20 during the fabricating of the plurality of point defects 20 enables controlling the interactions of the electronic spins at the plurality of point defects 20, i.e., interactions of spin magnetic moments of the electrons at the plurality of point defects 20. This interaction, scaling with l / r3(see above), enables entanglement of the interacting electronic spins.

[0104] FIG. 6A-6F shows results of simulating the NV-center based on the plurality of quantum states and plurality of transitions, shown in FIG. 1, using a quantum mechanical model. One example of the quantum mechanical model is the Lindblad master equation, which describes the time evolution of a density matrix p, involving a Hamiltonian H and Lindblad jump operators Lk. The Lindblad jump operators Lkdescribe the transitions using the transitions rates between the electronic states and / or the charge states (described above with reference to FIG. 1).

[0105] The Hamiltonian H of the Lindblad master equation includes a spin Hamiltonian. The spin Hamiltonian includes the electronic Zeeman energy as well as electron spin-spin interactions (magnetic dipole-diploe interactions) in the triplet ground3A2 and the triplet excited state3E of the negative charge state N V .

[0106] The quantum mechanical model describes the time evolution of the system shown in FIG. 1. Based on the time evolution of the system, time evolutions of the occupancies associated with the plurality of quantum states can be calculated. Based on the time evolutions of the occupancies, the photocurrent and / or the photoluminescence associated with the NV-center can be calculated.

[0107] In another aspect, nuclear spins, e.g., in the case of the NV-center, the nuclear spin of the nitrogen atom of the NV-center, and / or one or more of the nuclear spins of the carbon atoms and / or nitrogen atoms in a vicinity of the NV-center, may be included in the system shown in FIG. 1. Including the nuclear spins in the model enables simulating interactions of the nuclear spins, such as the hyperfine interactions between the electronic spins and the nuclear spins. The spin Hamiltonian may further include terms relating to the nuclear Zeeman energies, nuclear spin-spin interactions, and the hyperfine interaction between electronic spins and nuclear spins.

[0108] FIGS. 6 A and 6B show ionization dynamics for two different powers of the illumination laser 50. The illumination laser 50 illuminates a single NV-center (i.e., a single point defect 20) with the indicated laser power (1 mW or 3 mW) arranged in the semiconductor device 15 for an illumination duration of 5 ps. The laser power and the illumination duration are input parameters to the quantum mechanical model. Shown are the simulated electron current and the simulated hole current starting from different initialization states (the state3A2 with electronic spins ms= 0, ms= — 1, as indicated in the insets) for a duration of 3 ps (the case for ms= 1 is not shown in FIGS. 6A and 6B). The y-axis in FIGS. 6A and 6B indicate the electron current (left y-axis) and hole current (right y-axis) in MHz, i.e., in units of 106electrons / holes per second or, equivalently, 1 electron / hole per microsecond.

[0109] FIG. 6 A, which has been simulated for the laser power being 1 mW, indicates that for the case ms= — 1, over the course of several microseconds, approximately one electron is photoelectrically generated by ionization (see above). FIG. 6B, which has been simulated for the laser power being 4 mW, indicates that for the case ms= — 1, over the course of approximately 1 microsecond, approximately one electron is photoelectrically generated by ionization. According to these results, the single-electron electrometer 40 operating at an operation rate of at least 1 MHz enables the detection of a single charge carrier (i.e., of an electron or a hole).

[0110] In one aspect, the single-electron electrometer 40 comprises at least one transistor. The at least one transistor may be a single-electron transistor (SET) or a bipolar transistor. An example of the bipolar transistor is a single-electron bipolar avalanche transistor.

[0111] In one aspect, an input charge noise for the SET is smaller than the sensitivity required at the operation rate (or equivalently, operation bandwidth). In one aspect, the SET has an input charge noise floor of approximately 10-4e / VHz, resulting in an ability to detect single electrons at -1MHz. When the input charge noise floor is « 10-3e / VHz, single electrons may be measured at bandwidths > 1MHz.

[0112] As indicated by FIGS. 6A and 6B, the electron current and the hole current reach a substantially stationary value. Especially for the case of the laser power being 4 mW, the electron current and the hole current reach the substantially stationary value afterapproximately 2 ps. FIG. 6C shows the substantially stationary value reached by the photocurrent (indicated by “carriers” in the inset). FIG. 6C furthermore shows a substantially stationary value of a photon current (indicated by “photons” in the inset). The photon current is also shown in FIGS. 6D and 6E, which show the photoluminescence (“photodynamics”) due the electromagnetic driving signal exciting the NV-center (i.e., the point defect 20) with the laser power being 1 mW or 4 mW. As can be seen from FIG. 6C by comparison, the photon current saturates at a laser power of approximately 2 mW and remains substantially constant for values of the laser power between approximately 2 mW and 6 mW.

[0113] FIG. 6F shows a contrast for the photocurrent and the photoluminescence. The contrast is calculated according to with T being theintegration time (which is 1 ps for the simulation results shown) and p being the sum of the generation rates of electrons and holes shown FIGS. 6A and 6B or the generation rate of photons shown in FIGS. 6D and 6E, for different initialization states of the electronic spin as indicated. The contrast differentiates efficiently between the electron spin states (ms= 0, ms= — 1) where the value of the contrast is relatively large (the case for ms= 1 is not shown in FIGS. 6A and 6B). For the photocurrent, the contrast peaks at the laser power being approximately 4 mW. For the photoluminescence, the contrast peaks at the laser power being approximately 2 mW.

[0114] FIG. 7 shows the quantum information processing device 10 according to the disclosure. The quantum information processing device 10 comprises a base 12, on which the semiconductor device 15 is arranged. The semiconductor device 15 comprises a semiconductor substrate 16 and a doped layer 17 comprises dopants 23. The dopants 23 comprise electron acceptors and electron donors.

[0115] The doped layer 17 further comprises the plurality of point defects 20. The point defects 20 may be arranged in the doped layer 17 of the semiconductor device 15 during manufacturing. The point defects 20 may be arranged in semiconductor device 15 having a predetermined one of the defect distance (see above with reference to FIG. 3).

[0116] The quantum information processing device 10 further comprises a plurality of electrodes 30 arranged on the surface (mentioned above with reference to FIG. 3). Theplurality of electrodes 30 is electrically connected to a plurality of single-electron electrometers 40.

[0117] The electrodes are configured to collect electrons which are photogenerated from one or a plurality of point defects 20.

[0118] Electric field lines and electric field strength of an electric field at the location of one of the point defects 20 depend on parameters, such as a distance between the electrodes, a number of electrodes, a configuration of the electrodes (such as size, geometry and material of the electrodes), the distance of the electrodes to the one of the point defects 20 or the arrangement of the electrodes with respect to the one of the point defects 20.

[0119] The electric field may be generated by biasing the electrodes. The electric field guides the electrons to the electrodes. The electrons are then collected by the single-electron electrometer 40. It is possible to use different electrode configurations to collect the electrons. Examples of such different electrode configurations include, but are not limited to, planar electrode structures on a top surface of the semiconductor, or frontside electrodes and backside electrodes which can be further located from the point defects 20.

[0120] A selected one of the plurality of electrodes 30 may be arranged in a vicinity of a selected one of the plurality of point defects 20.

[0121] However, it will be appreciated that this represents only one option, i.e. the one or more electrodes 30 are not required to be arranged in the vicinity of a selected one of the point defects 20. As previously mentioned, the electric field at a point defect may be tailored by adjusting the position of the electrodes.

[0122] In one aspect, a single one of the single-electron electrometers 40 could be used per electrode pair. In another aspect, a single one of the single-electron electrometers 40 could be used per multiple electrodes.

[0123] The electromagnetic driving signal comprises one or more cycles. A single one of the cycles of the electromagnetic driving signal corresponds to a single ionization cycle of one or more of the point defects 20 interacting with the electromagnetic drive signal.

[0124] In a single ionization cycle (corresponding to one cycle of the electromagnetic driving signals), one of the NV centers can generate one electron. In a single ionization cycle, a number of M NVs can generate M electrons (one electron per NV).

[0125] In N ionization cycles (corresponding to N cycles of the electromagnetic driving signals), a single one of the NV centers can generate N electrons. In N ionization cycles (corresponding to N cycles of the electromagnetic driving signals), M NVs can generate M x N electrons.

[0126] If an electrode pair is configured to collect electrons from a single one of the point defects 20, a number of electrons collected by said pair of electrodes corresponds to the number of cycles N of the electromagnetic drive signal interacting with said single one of the point defects 20.

[0127] If an electrode pair is configured to collect electrons from M point defects 20, a number of electrons collected by said pair of electrodes corresponds to a product of the number of cycles N of the electromagnetic drive signal interacting with said M point defects and a number M of point defects 20.

[0128] A single electron may be collected by an electrode pair and be detected by the single-electron electrometer 40. Subsequently, properties of said collected single electron, such as a spin of the electron may be determined.

[0129] This collection allows analyzing the properties of individual ones of the collected electrons. Thus, a state of a qubit formed by the NV center from which the collected electron has been collected can be determined.

[0130] When more than one electron is collected by an electrode pair and detected by the single-electron electrometer 40, the properties of the individual collected electrons among said one or more of the collected electrons may be determined, for example by analyzing the features of the electrons in the time domain. Thus, the states of qubits formed by the NV centers from which the electrons have been collected can be determined.

[0131] For some of the electrodes, one single-electron electrometer 40 may be used per electrode pair, and for other ones of the electrodes, one single-electron electrometer 40 is used for several electrode pairs.

[0132] As shown in FIG. 7, the selected one of the plurality of point defects 20 may be associated with a unique one of the plurality of single-electron electrometers 40. Such arrangement enables the detection, by means of the unique one of the plurality of electrodes 30 associated with the selected one of the plurality of point defects 20, of the transferred electron, transferred by ionization from the selected one of the plurality of point defects 20 to the conduction band of the semiconductor device 15.

[0133] In one aspect, the plurality of point defects 20 may comprise the NV-centers arranged in the semiconductor device 15 being made of diamond. In another aspect, the plurality of point defects 20 may comprise the silicon vacancy and / or the carbon vacancy arranged in the semiconductor device 15 being made of silicon carbide.

[0134] The quantum information processing device 10 further comprises an electromagnetic source or light emitting and delivery device 50. An example of the electromagnetic source 50 is the illumination laser 50 mentioned above.

[0135] The electromagnetic source 50 may be arranged on a chip 12. The semiconductor device 15 may be arranged on the chip 12 alongside the electromagnetic source 50.

[0136] FIG. 8 shows a process for manufacturing the quantum information processing device 10. The manufacturing process comprises a first step SI 00, S20 of providing a semiconductor device 15. The first step SI 00, S20 of providing a semiconductor device 15 may comprise a step S100 of providing a chip 12. The first step S100, S20 of providing a semiconductor substrate 15 may further comprises a step S200 of fabricating the semiconductor substrate 15.

[0137] The method further comprises a step S400 of fabricating a plurality of point defects 20. The step S400 of fabricating a plurality of point defects 20 may comprise a step S300 of introducing impurities to the semiconductor substrate 15.

[0138] The method further comprises a step S500 of arranging a plurality of electrodes on the semiconductor substrate 15. The plurality of electrodes 30 may comprise gate electrodes. The plurality of electrodes 30 may further comprise control structures and read-out structures on the semiconductor substrate 15.

[0139] The method further comprises a step S600 of providing a plurality of single-electron electrometers 40 at the semiconductor substrate 15. The step S600 of providing the plurality of single-electron electrometers 40 comprises a step S700 of electrically connecting the plurality of single-electron electrometers 40 to the plurality of electrodes by means of transmission lines or electrical connections 35.List of reference numerals

Claims

Claims1. A quantum information processing device (10) comprising a semiconductor device (15), a plurality of electrodes (30) provided on at least one surface of the semiconductor device (15) and at least one single-electron electrometer (40) electrically connected to the semiconductor device (15) by the plurality of electrodes (30),- the semiconductor device (15) comprising a plurality of point defects (20) having a plurality of quantum states associated with at least one electron;- first transitions being effectible between first ones of the plurality of quantum states by means of electromagnetic signals interacting with the at least one electron;- second transitions occurring between second ones of the plurality of states; wherein at least some of the plurality of point defects (20) are arranged in the semiconductor device (15) at defect distances below 20 nm, and wherein the at least one single-electron electrometer (40) is configured to be operated at frequencies of 1 MHz or more.

2. The quantum information processing device (10) of claim 1, wherein the at least one single-electron electrometer (40) comprises an amplifier configured to be operated at frequencies of 1 MHz or more.

3. The quantum information processing device (10) of claim 2, wherein the amplifier comprises at least one of a single-electron transistor or a bipolar transistor.

4. The quantum information processing device (10) of any one of claims 1 to 3, further comprising an electromagnetic source (50) for generating the electromagnetic signals.

5. The quantum information processing device (10) of claim 4, wherein the electromagnetic source (50) is an optical source, and the electromagnetic signals are optical signals.

6. The quantum information processing device (10) of any one of claims 1 to 5, wherein the semiconductor device (15) further comprises impurities.

7. The quantum information processing device (10) of claim 6, wherein the impurities comprise electron donors and / or electron acceptors.

8. The quantum information processing device (10) of any one of claims 1 - 7, wherein the plurality of point defects (20) forms a two-dimensional array or a three-dimensional array.

9. The quantum information processing device (10) of any one of claims 1 - 8, wherein the plurality of point defects (20) forms a linear chain.

10. The quantum information processing device (10) of any one of claims 1 - 9, wherein at least some of the point defects (20) of the plurality of point defects (20) are arranged in the semiconductor device (15) at defect distances below 10 nm.

11. The quantum information processing device (10) of any one of claims 1 - 10, wherein the semiconductor device (15) comprises diamond.

12. The quantum information processing device (10) of any one of claims 1 - 11, wherein at least some of the point defects (20) are nitrogen-vacancy centers.

13. The quantum information processing device (10) of any one of claims 1 - 12, wherein the plurality of electrodes is arranged in pairs, and wherein the quantum information processing device (10) comprises, for at least some of the electrodes, a single one of the single-electron electrometer (40) per electrode pair.

14. The quantum information processing device (10) of any one of claims 1 - 13, wherein the plurality of electrodes is arranged in pairs, and wherein the quantum information processing device (10) comprises, for at least some of the electrodes, a single one of the single-electron electrometer (40) per several electrode pairs.

15. A method of manufacturing a quantum information processing device (10), the method comprising the steps of- providing (SI 00, S200) a semiconductor device (15);- fabricating a plurality of point defects (20),- having a plurality of quantum states associated with at least one electron;- first transitions being effectible between first ones of the plurality of quantum states by means of electromagnetic signals interacting with the at least one electron;- second transitions occurring between second ones of the plurality of states; and- at least some of the plurality of point defects (20) are arranged in the semiconductor device (15) at defect distances below 20 nm;- arranging a plurality of electrodes (30) on at least one surface of the semiconductor device (15);- electrically connecting the semiconductor device (15) with at least one singleelectron electrometer (40) via the plurality of electrodes (30), wherein the at least one single-electron electrometer (40) is configured to be operated at frequencies of 1MHz or more.

16. The method of claim 15, further comprising providing an electromagnetic source (50) for generating electromagnetic signals configured to interact with the plurality of point defects (20).

17. The method of claim 16, wherein the providing of an electromagnetic source (50) comprises providing an optical source.

18. The method of any one of claims 15 to 17, further comprising introducing impurities to the semiconductor device (15).

19. The method of any one of claims 15 to 17, further comprising arranging the semiconductor device (15) on a chip (12).

20. The method of claim 15, further comprising arranging the electromagnetic source (50) on the chip (12).

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