System and method for detection of spin states in a solid-state crystal

Abstract

A balanced photoelectric detection system for spin states in a solid-state material, the system comprising a first and a second junction on a solid-state material, each junction arranged on top of a plurality of active spin defects, a light source configured to excite at least one of the active spin defects on each of the first and second junctions, wherein the interaction of the light source with the first junction generates a first photocurrent in the first junction, and the interaction of the light source with the second junction generates a second photocurrent in the second junction, an emitter configured to emit signals interacting with at least one of the junctions, and a summing circuit configured to sum the first photocurrent with the second photocurrent, thereby generating a combined photocurrent. The present disclosure further relates to a method for photoelectric detection of spin states.

Description

[0001] P7500PC00

[0002] System and method for detection of spin states in a solid-state crystal

[0003] The present disclosure relates to a novel system and method for photoelectric detection of spin states in solid-state materials, such as the spin states of nitrogenvacancy (NV) defects in diamond-based structures.

[0004] Background

[0005] The state of the art in the field of spin state detection in nitrogen-vacancy (NV) centers in diamond, and generally in optically active spin defects in solid-state materials, relates to optically driven methods, where NV centers are excited using optical means such as laser sources. The spin populations can be subsequently estimated through optical detection techniques. However, these optical methods are often associated with substantial noise due to the intrinsic electromagnetic noise of the crystal, the low spin- related fluorescence contrast, and the inherent limitations of light extraction / collection the optical tools used, resulting in low signal-to-noise ratio (SNR) for the detection of spin populations. The technical overhead required to overcome these noise and contrast limitations poses challenges for the development of compact integrated systems which utilise the spin states as sensors or information processors.

[0006] To mitigate the above limitations, researchers have explored photoelectric detection techniques to facilitate integrated electronic application and improve the readout of spin states by generating a photo-induced current from NV centers in diamond structures. In this approach, a bias voltage is applied to an electrode hosting a number of NV centers, a laser excites the NV centers, triggering ground state to excited state transitions, while an AC current generator provides radio frequency signals to the NV centers. However, the generated photocurrent is proportional to the noise in the applied bias voltage, the noise in the laser excitation, and the noise of the AC field. Therefore, for an ensemble of spins, the SNR is usually lower than the spin-dependent current contrast, primarily due to the magnitude of dark current and the general noise associated with control and polarisation fields.

[0007] To address these challenges, advancements in photoelectric detection have incorporated lock-in detection techniques. Such a solution may reduce the noise of the generated photocurrent. However, the use of lock-in detection involves significant technical complexity, as it requires amplification, modulation, demodulation, and P7500PC00 filtering processes that increase system overhead and reduce the practical utility for all- electronic detection of spin resonances.

[0008] Hence, there is a need for a new integrated system approach that can further reduce the noise in the detection of spin states in solid-state materials, without requiring a complex and costly detection setup architecture.

[0009] Summary

[0010] One purpose of the present disclosure is to improve the detection of spin resonances of active spin defects in a solid-state material, such as in NV centers in diamond, by incorporating a balanced photoelectric detection scheme. Instead of having a single junction that is optically excited to generate a photocurrent, the present disclosure relates to the use of two such junctions configured in a balanced photodetection setup, each junction arranged on top of a plurality active spin defects. Utilizing a light source, the active spin defects on both junctions can be excited, thereby generating a photocurrent. The two photocurrents can be then subtracted before converted to an output voltage that can be used for further operations. Using such a technique can significantly improve the signal-to-noise ratio (SNR) of the system, as a plurality of noise sources cancel out when the two photocurrents are subtracted.

[0011] Specifically, the present disclosure relates to a photoelectric detection system for optically active defects in solid-state systems, the system comprising a first and a second junction on a solid-state material, such as a diamond-structure, each junction arranged on top of a plurality of active spin defects. For example, the first and the second junctions may be a set of electrodes, each set embedding a plurality active spin defects. Active spin defects may be any type of optically active defects in diamond, such as nitrogen vacancy centers or silicon vacancy centers. The first junction may be biased with a positive voltage, while the second junction may be biased with a negative voltage. Such opposite bias configuration enables the subtraction of noise-induced current, when the two generated photocurrent are combined. Further information and embodiments regarding the biasing techniques of the junctions are provided in the detailed description of the present disclosure. The term “junction” refers to a structure of a conducting material that is in contact with the solid-state material, thereby forming a junction where a current may flow. For example, a type of junction may be a gold lead which contacts a part of a solid-state material that has active spin defects, and a P7500PC00 second lead may also contact the part of the solid-state material that has active spin defects, thereby forming a conducting path where a photocurrent can be generated and flow through. The term “junction” may also be considered as a “conductor-crystal junction” wherein the conductor can be a metallic lead as written herein, and the crystal can be a solid-state material.

[0012] Moreover, the system may comprise a light source configured to excite at least one of the active spin defects on each of the first and second junctions, wherein the interaction of the light source with the first junction generates a first photocurrent in the first junction, and the interaction of the light source with the second junction generates a second photocurrent in the second junction. The light source can enable photoexcitation of the active spin defects. For NV centers in diamond, photoexcitation of the NV centers under a constant bias voltage promotes electrons from the valence band to the conduction band via the charge-state dynamics of the NV center and surrounding charge donors / acceptors. Applying a voltage bias across the surface of a junction while exciting the NV- system promotes their electrons into the conduction band. The resulting neutrally charged NV° center can then accept electrons from surrounding donors and from the valence band, thereby generating a finite photocurrent in the junction. The magnitude of the photocurrent depends on the vicinity and density of charge donors, and the general spin level population as the system is ionized. As a result, the photocurrent magnitude reflects the spin state population.

[0013] In order to process the generated photocurrent from the two junctions, the system may comprise an emitter, configured to emit signals interacting with at least one of the junctions. The purpose of such an emitter may be to emit signals that affect one of the two junctions, thereby influencing the spin populations, and the magnitude of the generated photocurrent. Such a feature can be beneficial, as it enables the two photocurrents to have different magnitudes before they are combined, effectively generating a combined photocurrent, where the noise stemming from various sources such as the emitter, or the light source, has been subtracted. The system may therefore comprise a summing circuit configured to sum the first photocurrent with the second photocurrent, thereby generating a combined photocurrent. Specifically, the current fluctuations resulting from noise from the light source or from the bias fields can be eliminated, via current subtraction at the summing circuit. Such a feature can P7500PC00 significantly enhance the signal-to-noise ratio for the detection of spin populations in a solid-state material.

[0014] In addition, depending on the type of application and the characteristics of the system, any type of noise sources may be eliminated during the current subtraction at the summing circuit. Specifically, the summing circuit may be configured to sum the first photocurrent with the second photocurrent such that current fluctuations originating from one or more noise sources are minimized, suppressed, or eliminated, thereby generating a combined photocurrent. Such a feature is beneficial, as the combined photocurrent can have improved signal-to-noise ratio, as the current fluctuations have been supressed. For example, noise from the junctions themselves, from the light source, from the emitter, or from the wiring of the system. By summing the first photocurrent with the second photocurrent, it is possible to minimize or eliminate current fluctuations originating from noise sources, such as from the light source or from magnetic fields originating from the emitter. The minimization or elimination of the current fluctuations can be performed via current subtraction at the summing circuit, thereby generating a combined photocurrent with improved signal-to-noise ratio. As described herein, the improved signal-to-noise ration can be achieved because the noise sources are subtracted when the first photocurrent is summed with the second photocurrent at the summing circuit.

[0015] In an embodiment, the one or more noise sources are selected from the group of: emitter, light source, first and second junction.

[0016] In an embodiment, the system can be configured wherein each junction is an interdigitated electrode. Using such electrodes can be beneficial, as interdigitation may increase the magnitude of the generated photocurrents, thereby enabling an easier processing of the photocurrent and larger signal-to-noise ratios.

[0017] Moreover, the system can be configured, such that the emitter is a device selected from the group of: AC current generator, magnetic field generator, or electric field generator. For example, an AC current generator may be utilized to emit radio frequency (RF) signals. Such RF signals can interact with a plurality of active spin defects in a junction, thereby affecting the spin populations of that junction, and influencing the generated photocurrent. For example, if the frequency of the emitter is P7500PC00 in resonance with a spin transition of the active spin defects in a junction, then a dip in the generated photocurrent can be detected, due to the carriers decaying through the active spin defects shelving states. Therefore, using an emitter can be a way to manipulate the generated photocurrents, and optimize the system to minimize the noise.

[0018] The present disclosure further relates to a method for photoelectric detection of spin states in a balanced photoelectric detection system, such as in a solid-state material, the method comprising the steps of exciting at least one active spin defect in a first junction to generate a first photocurrent, exciting at least one active spin defect in a second junction to generate a second photocurrent, emitting signals interacting with at least one of the two junctions, and combining the first and the second photocurrent, generating a combined photocurrent.

[0019] The system of the present disclosure can be applied to any type of solid-state material where a photocurrent can be driving a sub-bandgap manifold, and it is not limited to diamond-based structures. For example, as long a spin defect exists in a material, wherein such spin defect can be excited using a light source, the balanced photoelectric detection system of the present disclosure can be applied in order to e.g. extract the spin populations of the active spin defects. Such materials can be, but are not limited to: nitrogen-vacancy (NV) centers, silicon-vacancy (SiV) centers, germanium-vacancy (GeV) centers, tin-vacancy (SnV) centers in diamond, silicon- vacancy defects, divacancies, carbon antisite-vacancy pairs in silicon carbide (SiC) magnesium-related defects, gallium vacancies in gallium nitride (GaN), oxygen vacancies and zinc interstitials in zinc oxide (ZnO), oxygen vacancies or transitionmetal dopants in strontium titanate (SrTiO3), transition-metal impurities such as chromium or manganese in aluminum nitride (AIN), boron vacancies and carbon- related defects in hexagonal boron nitride (h-BN), sulfur or selenium vacancies in transition metal dichalcogenides such as molybdenum disulfide (MoS2), tungsten disulfide (WS2), molybdenum diselenide (MoSe2), phosphorus vacancies in indium phosphide (InP), dangling bonds and hydrogen-related states in amorphous silicon (a- Si), oxygen-deficiency centers in silica (SiO2), or sulfur or selenium-related defect states in chalcogenide glasses. P7500PC00

[0020] Description of Drawings

[0021] Various embodiments are described hereinafter with reference to the drawings. The drawings are examples of embodiments and are intended to illustrate some of the features of the presently disclosed balanced photoelectric detection of states in a solid- state material and are not limiting to the presently disclosed system and method.

[0022] Fig. 1 shows a cross-section of junction arranged on top of a plurality of active spin defects.

[0023] Fig. 2 shows an example of a balanced photoelectric detection system for spin states in diamond.

[0024] Fig. 3 shows a measurement of photocurrent in arbitrary units from a d junction as a function of frequency.

[0025] Fig. 4 shows a schematic of a current splitter comprising two transistors and a cascode transistor.

[0026] Fig. 5 shows the steps of a method for photoelectric detection of spin states in a solid- state material.

[0027] Fig. 6 shows an embodiment of a balanced photoelectric detection system comprising a current splitter.

[0028] Detailed description

[0029] A purpose of the present disclosure is to minimize the noise in detection of spin states in a solid-state material, such as in a diamond structure, by utilizing a balanced photoelectric detection system for spin states, which improves the signal-to-noise ratio (SNR) in detecting spin populations of active spin defects such as nitrogen-vacancy (NV) centers or any other optically active defects in solid-state materials. Specifically, the present disclosure relates to a balanced photoelectric detection system for spin states in a solid-state material, the system comprising a first and a second junction on a solid-state material, each junction arranged on top of a plurality of active spin defects, a light source configured to excite at least one of the active spin defects on each of the first and second junctions, wherein the interaction of the light source with the first junction generates a first photocurrent in the first junction, and the interaction of the light source with the second junction generates a second photocurrent in the second junction, an emitter configured to emit signals interacting with at least one of the P7500PC00 junctions, and a summing circuit configured to sum the first photocurrent with the second photocurrent, thereby generating a combined photocurrent.

[0030] The first junction and a second junction may be both integrated onto a solid-state material, such as a diamond-based structure. For example, metallic leads can be designed in a diamond-based structure, and such leads can be designed to embed a plurality of active spin defects in a gap. Therefore, by applying a bias between the leads and exciting the plurality of active spin defects with a light source, it is possible to generate a photocurrent along the leads. A cross-section of a junction can be seen in Fig. 1 . Two leads 100 are separated by a gap 104, wherein the two leads are arranged on top of a plurality of active spin defects 101 . A bias voltage can be applied, and a light source 102 may be utilized to irradiate the area of the gap. Such a process can generate a current along the junction.

[0031] The light source may be any type of light source capable of irradiating the plurality of active spin defects and triggering a transition from a ground state to an excited state. For example, for NV centers in diamond, such a transition can be from the triplet ground state3A to the triplet excited state3E. The purpose such transitions are to activate the cycle of transmitting an electron to the conduction band, and receiving an electron from a donor or from the valence band. Such a process can be performed continuously, leading to the formation of a current across a junction. Furthermore, the light source may illuminate one of the two junctions, or the light source may illuminate both junctions simultaneously. Depending on the type of application or experiment, different illumination methods may be used. For example, by illuminating one of the two junctions, it is possible to extract common mode rejection of the intrinsic dark current, thereby effectively calibrating the system and reducing the noise of the combined photocurrent.

[0032] The emitter can be advantageous to use, in order to emit signals interacting with at least one of the junctions. The emitter may deliver an AC field, radiofrequency (RF) signals, or other electromagnetic stimuli that influence the spin populations in one or both junctions. By selectively interacting with one junction, the emitter may facilitate the generation of photocurrents that can be modulated based on the spin transitions of the active spin defects. As also discussed in the previous paragraphs, the use of an emitter P7500PC00 can be important, as an emitter enables to tune the magnitude of a photocurrent while allowing the subtraction of noise sources when the two photocurrents are added.

[0033] The summing circuit may combine the first and second photocurrents to generate a combined photocurrent. The summing process may involve either subtraction (e.g., differential mode) or addition of the two photocurrents, depending on the configuration of the summing circuit and the bias configuration of the two junctions. The purpose of this step is to reduce noise stemming from sources such as instabilities in the light source, variations in the bias voltage applied to the junctions, environmental electromagnetic interference, or any other system-level fluctuations.

[0034] As a result, by employing a balanced detection configuration, the system enhances the SNR, as common-mode noise may be effectively canceled during the summing process. The system of the present disclosure minimizes the noise in the combined photocurrent, providing a more accurate representation of the spin populations. In addition, the described system enables the detection of spin states with improved precision and reduced technical complexity compared to existing methods, such as lock-in detection techniques.

[0035] Figure 2 shows a schematic of a balanced photoelectric detection system for spin states in a solid-state material. A first junction 200 and a second junction 201 can be connected in a circuit, such that each junction is arranged on top of a plurality of active spin defects. Each of these junctions may also be modeled as an RC circuit, since there is capacitive coupling between the leads of each junction. In this example, the first junction is biased with a positive voltage V+203, and the second junction is biased with a negative voltage V. 202. Each junction is irradiated using a light source 204 in order to trigger ground state to excited state transitions in the plurality of active spin defects. The light source in combination with the applied bias causes a first photocurrent 206 to be generated in the first junction, and a second photocurrent 205 in the second junction. A summing circuit 207 is utilized to combine the two photocurrents into a combined photocurrent. For example, such a summing circuit may be a junction where the two photocurrent are subtracted. In an embodiment, the combined P7500PC00 photocurrent may be converted to an output voltage 208, by utilizing a current-to- voltage converter 209.

[0036] In an embodiment, the system can be configured such that the solid-state material is a diamond-based structure. The diamond-based structure may host a variety of optically and electromagnetically active defects, such as nitrogen-vacancy (NV) centers or silicon-vacancy (SiV) centers. In addition, the system can be configured, such that the active spin defects are optically and electromagnetically active defects in diamond, such as nitrogen vacancy (NV) centers or silicon-vacancy (SiV) centers.

[0037] Junction characteristics

[0038] In one embodiment of the present disclosure, the system can be configured such that each junctions may be an interdigitated electrode. Such a configuration may enhance the collection efficiency of photocurrents by increasing the surface area available for charge collection. The interdigitated structure may also promote uniform electric field distribution, ensuring consistent excitation and charge movement across the active spin defects. This design may be particularly beneficial in applications requiring high sensitivity, such as quantum sensing or precision metrology.

[0039] Furthermore, the system can be configured such that each junction is voltage-biased to facilitate efficient photocurrent generation. Voltage biasing may also allow precise control of system parameters, enabling tunability for various operational requirements. In an embodiment, the same voltage amplitude may be used for both junctions, and a DC or AC voltage may be utilized.

[0040] In another embodiment, the system can be configured such that each junction may be biased with a voltage preferably within the range from ±5 V to ±30 V. This range may provide sufficient field strength to drive charge carrier dynamics without risking damage to the solid-state material or introducing excessive noise. Such biasing conditions may be particularly useful for applications requiring stable and repeatable performance over long periods. Depending on the type of application and the type of active spin defects, different voltage ranges may be applied. In addition, the voltage values applied can P7500PC00 vary and may depend on the defect composition of the diamond, the design of the junctions and the modulation protocol used to coherently control the spin states.

[0041] Alternatively, the system can be configured such that the two junctions may be biased with opposite polarity. Opposite polarity biasing may enable the system to naturally cancel out common-mode noise sources, such as environmental fluctuations or noise from the light source, when the two photocurrents are combined. Such a setup may significantly improve the signal-to-noise ratio, enhancing the reliability of spin state detection.

[0042] Moreover, the system can be configured such that the two junctions may instead be biased with the same polarity using a differential pair process. Such an approach may simplify the design of the summing circuit while still enabling effective noise reduction. The symmetry of the biasing may also ensure consistent performance across both junctions, making the system more robust in challenging operating conditions. One goal of such biasing methods is that the current fluctuations based on common-mode voltage noise can be cancelled out, thereby increasing the signal-to-noise ration of the system.

[0043] Furthermore, the active spin defects in the solid-state material may be optically and electromagnetically active defects, such as nitrogen-vacancy (NV) centers or silicon- vacancy (SiV) centers. The present disclosure can be configured to operate with any type of two-level system in a diamond structure, with the requirement that such two- level system can be driven optically. Additional examples may include engineered defects like germanium-vacancy (GeV) centers or other color centers exhibiting similar properties.

[0044] In an embodiment, the system can be configured such that the summing circuit may comprise a current-to-voltage converter configured to convert the combined photocurrent into an output voltage. This conversion may enable seamless integration with standard electronic systems for further signal processing or data acquisition. The use of a current-to-voltage converter may also improve the dynamic range of the detection system, enabling the measurement of low-magnitude photocurrents. The current-to-voltage converter may also comprise additional components, such as low- pass filters, high-pass filter or techniques to optimize the processing of the P7500PC00 photocurrents. Further embodiments are disclosed in the following sections of the detailed description.

[0045] Emitter characteristics

[0046] Moreover, the system can be configured such that the emitter may be a device selected from the group of an AC current generator, a magnetic field generator, or an electric field generator. As written in the previous sections, the purpose of the emitter is to influence the spin populations of one of the two junctions. Such an influence can be achieved via various techniques. Each of these emitters may provide specific stimuli to interact with the spin defects, such as resonant excitation of spin transitions or modulation of the photocurrent. For example, a magnetic field generator may be used to align spin states, while an AC current generator may deliver radio frequency (RF) signals to induce spin transitions. A gradient static magnetic field may be applied such that one junction relates to spins with transitions tuned to a ground or excited-state level anti-crossing, while the other junction does not, due to the decaying DC field. Under these conditions, spin-state transitions can be immediately driven by incoherent light excitation. Other possibilities may involve applying electric field gradients or depositing a surface acoustic wave generator in the vicinity of a junction, which can drive particular phonon transitions thereby affecting spin polarization dynamics under continuous excitation.

[0047] Figure 3 shows a measurement of photocurrent in arbitrary units 300 from a junction as a function of frequency 301 of an AC current generator. When the frequency of the AC current generator is on resonance with an excitation of active spin defects, a dip in the photocurrent is detected 302. Such a feature can be utilized by the presently claimed system in order to manipulate the photocurrent of one of the two junctions and optimize the signal-to-noise ration of the combined photocurrent.

[0048] In an embodiment, the signals emitted by the emitter may interact with only one of the two junctions. Such an effect can be achieved by arranging the emitter at a close distance to one of the junctions, while at a further distance from the second junction. This selective interaction may enable differential measurements, where changes in the photocurrent of the targeted junction can be compared against the second junction. As also described in the previous sections, such an approach may isolate specific effects while minimizing the influence of background noise. Moreover, the emitter may be P7500PC00 configured to interact with both junctions in different ways. For example, the transmitted signals may be phase shifted before they interact with the second junction. Such a phase shift may result in a different interaction with the active spin defects of the second junction.

[0049] In another embodiment, the emitter may be an AC current generator, wherein said AC current generator may be a transmission line, an antenna, or a resonator. Such a configuration may allow efficient delivery of RF signals to the active spin defects, ensuring optimal interaction with their spin states. The RF frequency may preferably range from 0.1 kHz to 50 GHz, allowing for versatile operation across a broad spectrum of spin transitions. Depending on the type of active spin defects or the density of the active spin defects in the solid-state material, the frequency and / or the magnitude of the RF signals may be modified.

[0050] For the embodiment wherein the emitter is an AC current generator, the AC current generator can be configured to emit RF signals that are circularly polarized. Circular polarization may enhance the efficiency of spin-selective transitions by aligning with the quantum mechanical properties of the spin defects. This feature may be particularly advantageous in experiments requiring precise control of spin state populations.

[0051] The summing circuit may be configured to sum the in-phase component of the first photocurrent with the in-phase component of the second photocurrent. This approach may ensure that only the relevant spin-dependent signal is amplified, while noise contributions that are out of phase are suppressed. This feature may improve the fidelity of the detected signal, making the system suitable for high-precision applications. The first and second photocurrent may be DC signals or AC signals. For example, they can be independently or identically modulated, and they may form a differential pair. For instance, both the first and second photocurrent may be modulated with opposite phases for a particular modulation scheme. Depending on the type of application, different characteristics of the signals and the applied bias can be used.

[0052] Light source characteristics

[0053] In an embodiment, the system can be configured such that the light source is linearly polarized. In addition, the system can be configured such that the light source is circularly polarized. Linearly polarized light may provide uniform excitation across the P7500PC00 solid-state material, while circularly polarized light may enhance specific transitions within the spin defects. The light source may be a coherent source such as a laser, or it may be an incoherent light source with bandpass filtering.

[0054] The system can be configured, such that the light source emits signals with wavelengths preferably larger than 300 nm and preferably smaller than 750 nm. Depending on the type of active spin defects, different light source wavelengths may be chosen. For example, for NV centers, a wavelength between 650 nm and 250 nm is suitable. For silicon vacancy (SiV) centers, a wavelength range between 750 nm and 300 nm may be used, and for germanium vacancy centers, a wavelength range between 650 nm and 300 nm may be used. The light source may also have a modulated wavelength source, which may tune the wavelength or the frequency of the irradiated light. As also described in the previous sections, the purpose of the light source is to excite at least one of the active spin defects by driving transitions between a ground state and an excited state on each active spin defect.

[0055] Current splitter

[0056] In one embodiment, the system can be configured such that the summing circuit comprises a current splitter circuit. One purpose of the current splitter circuit is to optimize the processing of the two photocurrents, in order to minimize the noise regardless of the relative magnitude of the two photocurrents. For example, if the density of the active spin defects is different in the first junction compared to the second junction, then that would lead to higher magnitude of the first photocurrent compared to the second photocurrent. As a result, the current splitter circuit may be utilized to calibrate the system and provide a high signal-to-noise combined photocurrent regardless of the magnitude of the first and second photocurrent.

[0057] Furthermore, the system can be configured such that the current splitter may include a transistor pair, configured to ensure that the combined photocurrent remains independent of the individual photocurrent values. This feature may improve the accuracy and reliability of noise cancellation in the system. Using such a feature may ensure that the combined photocurrent is independent of the values of the first and second photocurrent, but rather the dependent on the ratio of the two photocurrents. In an embodiment, the transistor pair may be any type of suitable transistor pairs, such as bipolar junction transistors or FET transistor-based current mirrors. Depending on the P7500PC00 type of application, a certain transistor pair may be selected to optimize the functionality of the system.

[0058] In addition, the system can be configured, such that the current splitter comprises a cascode transistor guiding the photocurrent of the first junction to the current splitter circuit. Such an arrangement may improve signal stability and reduce the impact of parasitic capacitance, ensuring consistent performance under varying conditions.

[0059] An example of how the two transistors and the cascode transistor can be set is shown in Fig. 4. The depicted circuit illustrates the functionality of two conductor-diamond junctions 400 generating photocurrents, which are combined using the summing circuit. In this example, the upper junction is biased with a positive voltage V+while the lower junction is biased with a negative voltage V_. Each junction may be illuminated by a light source excitation 401 , generating a photocurrent on each junction. The magnitude of the photocurrent depends on the density of the spin defects. The first and second photocurrent may be summed at the summing circuit 402. This summation is critical for the noise-cancelling design of the system, as it may reduce the common-mode noise that affects both photocurrents. A series of transistor can be used in order to improve the processing of the photocurrents. A cascode transistor 403 may be used in order to prevent the capacitance of the first junction from overloading the summing circuit. Two transistors 404, 405, which may preferably be bipolar junction transistors, may be used to ensure that the current summation between the two junctions is independent of their actual relative value, but rather dependent to the current ratio in the current splitter. Such a design can leverage the differential biasing of the junctions and the summing circuit to enhance the signal-to-noise ratio. Such a current splitter configuration may be

[0060] P7500PC00 combined with a current-to-voltage converter as shown in Fig. 2, in order to optimize the voltage that is outputted from the system.

[0061] Moreover, the system may further comprise a negative-feedback amplifier, enabling continuous matching of the first photocurrent and the second photocurrent, thereby optimizing the noise cancellation. Furthermore, the system can be configured such that the current splitter circuit may comprise a regulating resistor to act as a tunable high- pass filter. This configuration may suppress low-frequency noise, further enhancing the signal quality. In an embodiment, the system may comprise a transimpedance amplifier, converting current fluctuations to voltage fluctuations. The regulating resistor may be used in combination with the transimpedance amplifier, with the purpose of tuning the frequency range that can be transmitted through the amplifier. In an embodiment, the regulating resistor enables the current splitter to act as a high-pass filter that can be tuned to allow different frequency thresholds. Additionally, the summing circuit may comprise an amplifier, such as an operational amplifier, to enhance the signal strength for subsequent processing.

[0062] The present disclosure further relates to a method for photoelectric detection of spin states in a balanced photoelectric detection system, such as in a solid-state material. The method comprises the steps of exciting at least one active spin defect in a first junction to generate a first photocurrent 500, exciting at least one active spin defect in a second junction to generate a second photocurrent 501 , emitting radio frequency (RF) signals interacting with at least one of the two junctions 502, and combining the first and the second photocurrent, generating a combined photocurrent 503. The steps of the method are shown in Fig. 5.

[0063] Furthermore, the method may incorporate elements from any of the described system embodiments, such as using interdigitated electrodes, applying voltage biases, or employing advanced summing circuits.

[0064] P7500PC00

[0065] The system may be powered using any suitable power source, including but not limited to batteries, DC power supplies, or AC-to-DC converters. In one example, the power source may provide a regulated voltage within the range necessary to operate the junctions, the emitter, the light source, and the summing circuit. The system may also include a power management module configured to distribute power to the various components efficiently, ensuring stable operation and minimizing power consumption.

[0066] Furthermore, the system may include a processor configured to control the operations of the various components. For instance, the processor may be operatively connected to the light source, the emitter, and the summing circuit to coordinate the excitation of the active spin defects, the generation of electromagnetic fields, and the processing of photocurrents. The processor may execute software or firmware routines to optimize system performance, such as by dynamically adjusting bias voltages, tuning the emitter frequency, or filtering noise from the combined photocurrent.

[0067] In addition, the system may include a data storage module, for storing operational parameters, measurement data, or calibration settings. For example, the data storage module may record the intensity and timing of the photocurrents generated by the junctions, enabling further analysis of spin states. Stored data may also include predefined configurations for specific applications, such as spin resonance detection or quantum sensing.

[0068] In one embodiment, the processor may be connected to a user interface, such as a graphical display or a control panel, to allow real-time monitoring and adjustment of system settings. Alternatively, the system may include a communication interface, such as a wired or wireless connection, to transmit data to an external device or to receive remote instructions for operation.

[0069] P7500PC00

[0070] Examples

[0071] Figure 6 shows an example of a current splitter connected to a balanced photoelectric detection system for spin states in a solid-state material. This schematic presents an extension of the circuit of figure 4. The cascode transistor 600 and the bipolar junction transistors 601 , 602 may be used to stabilize and amplify the combined photocurrent. After amplification, the combined photocurrent may be fed into a common mode noise rejection 603, such as a first operational amplifier comprising a resistor and a capacitor in a feedback loop. The resistor may act as a regulating resistor enabling the current splitter circuit to act as a tunable high-pass filter. Such a configuration may be used to extract the linear component of the combined photocurrent signal. In addition, the combined photocurrent can be routed through a second path to a feedback loop 604 such as a second operational amplifier. Such a system may be used to output a linear output or a logarithmic output of the voltage.

[0072] Further details

[0073] 1 . A balanced photoelectric detection system for spin states in a solid-state material, the system comprising a first and a second junction on a solid-state material, each junction arranged on top of a plurality of active spin defects, a light source configured to excite at least one of the active spin defects on each of the first and second junctions, wherein the interaction of the light source with the first junction generates a first photocurrent in the first junction, and the interaction of the light source with the second junction generates a second photocurrent in the second junction, an emitter configured to emit signals interacting with at least one of the junctions, and a summing circuit configured to sum the first photocurrent with the second photocurrent such that current fluctuations originating from one or more noise sources are minimized or suppressed, thereby generating a combined photocurrent.

[0074] 2. The system according to item 1 , wherein the solid-state material is a diamondbased structure. P7500PC00

[0075] 3. The system according to any one of the preceding items, wherein each junction is an interdigitated electrode.

[0076] 4. The system according to any one of the preceding items, wherein each junction is voltage-biased.

[0077] 5. The system according to item 4, wherein each junction is voltage-biased with a voltage preferably within the range from ±5 V to ±30 V.

[0078] 6. The system according to any one of the items 4-5, wherein the two junctions are biased with opposite polarity.

[0079] 7. The system according to any one of the items 4-5, wherein the two junctions are biased with the same polarity using a differential pair process.

[0080] 8. The system according to any one of the preceding items, wherein the active spin defects are optically and electromagnetically active defects in diamond, such as nitrogen vacancy (NV) centers or silicon-vacancy (SiV) centers.

[0081] 9. The system according to any one of the preceding items, wherein the summing circuit comprises a current-to-voltage converter, configured to convert the combined photocurrent to an output voltage.

[0082] 10. The system according to any one of the preceding items, wherein the emitter is a device selected from the group of: AC current generator, magnetic field generator, or electric field generator.

[0083] 11 . The system according to any one of the preceding items, wherein the signals emitted by the emitter are interacting with only one of the two junctions.

[0084] 12. The system according to item 10, wherein the AC current generator is a transmission line, an antenna, or a resonator. P7500PC00

[0085] 13. The system according to item 10, wherein the AC current generator emits RF signals with frequency preferably in the range between 0.1 kHz to 50 GHz.

[0086] 14. The system according to any one of the preceding items, wherein the emitter is positioned such that emitted signals are only interacting with one of the two junctions.

[0087] 15. The system according to any item 10, wherein the AC current generator is configured to emit radio frequency (RF) signals that are circularly polarized.

[0088] 16. The system according to any one of the preceding items, wherein the summing circuit sums the in-phase component of the first photocurrent with the in-phase component of the second photocurrent.

[0089] 17. The system according to any one of the preceding items, wherein the light source is linearly polarized.

[0090] 18. The system according to any one of the preceding items, wherein the light source is circularly polarized.

[0091] 19. The system according to any one of the preceding items, wherein the light source emits signals with wavelengths preferably larger than 300 nm, and preferably smaller than 750 nm.

[0092] 20. The system according to any one of the preceding items, wherein the light source is configured to excite at least one of the active spin defects by driving transitions between a ground state and an excited state on each active spin defect.

[0093] 21 . The system according to any one of the preceding items, wherein the summing circuit comprises a current splitter circuit. P7500PC00

[0094] 22. The system according to item 21 , wherein the current splitter circuit comprises two transistors configured to ensure that the combined photocurrent is independent to the value of each of the two photocurrents, such as bipolar junction transistors or FET transistor-based current mirrors.

[0095] 23. The system according to any one of the items 21 -22, further comprising a negative-feedback amplifier, enabling continuous matching of the first photocurrent and the second photocurrent, thereby optimizing the noise cancellation.

[0096] 24. The system according to any one of the items 21 -22, wherein the current splitter circuit comprises a regulating resistor enabling the current splitter circuit to act as a tunable high-pass filter.

[0097] 25. The system according to any one of the preceding items, wherein the summing circuit comprises an amplifier, such as an operational amplifier.

[0098] 26. The system according to any one of items 21 -23, further comprising a cascode transistor guiding the photocurrent of the first junction to the current splitter circuit.

[0099] 27. The system according to any one of the preceding items, wherein the one or more noise sources are selected from the group of: emitter, light source, first and second junction.

[0100] 28. A method for photoelectric detection of spin states in a balanced photoelectric detection system, such as a solid-state material, the method comprising the steps of exciting at least one active spin defect in a first junction to generate a first photocurrent, exciting at least one active spin defect in a second junction to generate a second photocurrent, emitting signals interacting with at least one of the two junctions, and P7500PC00 combining the first and the second photocurrent, generating a combined photocurrent.

[0101] 29. The method according to item 28, wherein the steps of the method are according to any one of the items 1 -27.

Claims

22P7500PC00Claims1 . A balanced photoelectric detection system for spin states in a solid-state material, the system comprising a first and a second junction on a solid-state material, each junction arranged on top of a plurality of active spin defects, a light source configured to excite at least one of the active spin defects on each of the first and second junctions, wherein the interaction of the light source with the first junction generates a first photocurrent in the first junction, and the interaction of the light source with the second junction generates a second photocurrent in the second junction, an emitter configured to emit signals interacting with at least one of the junctions, and a summing circuit configured to sum the first photocurrent with the second photocurrent, thereby generating a combined photocurrent.

2. The system according to claim 1 , wherein the solid-state material is a diamondbased structure.

3. The system according to any one of the preceding claims, wherein each junction is an interdigitated electrode.

4. The system according to any one of the preceding claims, wherein each junction is voltage-biased.

5. The system according to any one of the claims 3-4, wherein the two junctions are biased with opposite polarity.

6. The system according to any one of the claims 3-4, wherein the two junctions are biased with the same polarity using a differential pair process.

7. The system according to any one of the preceding claims, wherein the summing circuit comprises a current-to-voltage converter, configured to convert the combined photocurrent to an output voltage.P7500PC008. The system according to any one of the preceding claims, wherein the signals emitted by the emitter are interacting with only one of the two junctions.

9. The system according to any one of the preceding claims, wherein the summing circuit comprises a current splitter circuit.

10. The system according to claim 9, wherein the current splitter circuit comprises two transistors configured to ensure that the combined photocurrent is independent to the value of each of the two photocurrents, such as bipolar junction transistors or FET transistor-based current mirrors.11 . The system according to any one of the claims 9-10, further comprising a negative-feedback amplifier, enabling continuous matching of the first photocurrent and the second photocurrent, thereby optimizing the noise cancellation.

12. The system according to any one of the claims 9-11 , wherein the current splitter circuit comprises a regulating resistor enabling the current splitter circuit to act as a tunable high-pass filter.

13. The system according to any one of claims 9-11 , further comprising a cascode transistor guiding the photocurrent of the first junction to the current splitter circuit.

14. A method for photoelectric detection of spin states in a balanced photoelectric detection system, such as a solid-state material, the method comprising the steps of exciting at least one active spin defect in a first junction to generate a first photocurrent, exciting at least one active spin defect in a second junction to generate a second photocurrent, emitting signals interacting with at least one of the two junctions, and combining the first and the second photocurrent, generating a combined photocurrent.P7500PC0015. The method according to claim 14, wherein the balanced photoelectric detection system is the system according to any one of the claims 1 -13.

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