Periodic Reporting for period 4 - Q-DIM-SIM (Quantum spin simulators in diamond)
Okres sprawozdawczy: 2021-07-01 do 2022-06-30
The project's ultimate goal is to construct a quantum simulator based on NV centers in diamond. As detailed in the description of the action, several intermediate steps are required toward reaching this goal. These objectives are described below, along with the relevant achievements made in the project:
- Sample preparation: Relevant diamond samples (with high NV density and good coherence properties) are not available (either commercially or otherwise), and must be designed and fabricated specifically. For that purpose, we have employed commercial nitrogen ion implantation into high-purity samples purchased, creating the desired nitrogen concentration, although at a lower NV concentration than desired. We have then developed a local electron irradiation process using our in-house TEM (transmission electron microscope) system, increasing our NV concentration by an order of magnitude, thus reaching the NV-NV interaction regime, without adversely affecting the NV coherence properties (since no additional noise sources have been incorporated).
We are further studying novel surface termination techniques (in collaboration with Alon Hoffman’s group at the Technion) to enhance the quantum properties shallow NVs.
- Noise characterization: The coherence properties of NVs must be studied and understood precisely in order to reach the desired parameters and properly fabricate the diamond substrate. We have developed a novel noise spectroscopy scheme, based on continuous, phase modulated driving of the NV, which acts as a sensor for the noise affecting it. This technique, referred to as gDYSCO, provides enhanced resolution and accuracy in extracting the noise spectrum of non-monotonous sources. We showed that combining this approach with our previously demonstrated pulsed techniques can optimize resolution, accuracy and bandwidth.
- Many-body Hamiltonian engineering: Advanced control techniques are required in order to identify and modify NV-NV interactions, enabling precise determination of the system parameters (specifically in the presence of noise), as well as the engineering of desired interacting Hamiltonians in order to simulate quantum many-body problems of interest. We devised a protocol consisting of combined dynamical decoupling and homonuclear decoupling sequences to characterize the interacting spin system. In addition, we have developed a novel theoretical framework for general Hamiltonian engineering in interacting spin-1/2 systems, utilizing a group theory approach and an extended symmetry group (icosahedral symmetry) compared to the cubic group used before. We have shown that this framework leads to complete control over the quantum interacting spin system, beyond the capabilities afforded by the previous approach.
- Design superconducting couplers: We have analyzed the problem using a Green's function approach, leading to analytical, closed-form expressions for somewhat simplified, yet relevant, geometries. These results are helpful in determining the functional dependence of the couplers' performance on various parameters (such as shape and distance), informing the design and fabrication of these structures. We have also expanded our analysis to more complex geometries.
- Sample preparation: Relevant diamond samples (with high NV density and good coherence properties) are not available (either commercially or otherwise), and must be designed and fabricated specifically. For that purpose, we have employed commercial nitrogen ion implantation into high-purity samples purchased, creating the desired nitrogen concentration, although at a lower NV concentration than desired. We have then developed a local electron irradiation process using our in-house TEM (transmission electron microscope) system, increasing our NV concentration by an order of magnitude, thus reaching the NV-NV interaction regime, without adversely affecting the NV coherence properties (since no additional noise sources have been incorporated).
We are further studying novel surface termination techniques (in collaboration with Alon Hoffman’s group at the Technion) to enhance the quantum properties shallow NVs.
- Noise characterization: The coherence properties of NVs must be studied and understood precisely in order to reach the desired parameters and properly fabricate the diamond substrate. We have developed a novel noise spectroscopy scheme, based on continuous, phase modulated driving of the NV, which acts as a sensor for the noise affecting it. This technique, referred to as gDYSCO, provides enhanced resolution and accuracy in extracting the noise spectrum of non-monotonous sources. We showed that combining this approach with our previously demonstrated pulsed techniques can optimize resolution, accuracy and bandwidth.
- Many-body Hamiltonian engineering: Advanced control techniques are required in order to identify and modify NV-NV interactions, enabling precise determination of the system parameters (specifically in the presence of noise), as well as the engineering of desired interacting Hamiltonians in order to simulate quantum many-body problems of interest. We devised a protocol consisting of combined dynamical decoupling and homonuclear decoupling sequences to characterize the interacting spin system. In addition, we have developed a novel theoretical framework for general Hamiltonian engineering in interacting spin-1/2 systems, utilizing a group theory approach and an extended symmetry group (icosahedral symmetry) compared to the cubic group used before. We have shown that this framework leads to complete control over the quantum interacting spin system, beyond the capabilities afforded by the previous approach.
- Design superconducting couplers: We have analyzed the problem using a Green's function approach, leading to analytical, closed-form expressions for somewhat simplified, yet relevant, geometries. These results are helpful in determining the functional dependence of the couplers' performance on various parameters (such as shape and distance), informing the design and fabrication of these structures. We have also expanded our analysis to more complex geometries.
This project focuses on establishing a novel framework for quantum simulations of many-body spin systems using NV centers in diamond. As part of this overarching goal, several new and unconventional techniques have been employed, both advancing toward the main goal but also offering additional insights and capabilities in related fields and research directions.
We detail these methodologies below, based on the achievements described above:
- New technique for local, in-house electron irradiation using TEM:
We have used spatially localized irradiation based on in-house available TEM equipment, demonstrating improved NV concentrations in commonly available and implanted samples, without adversely affecting the NV coherence properties.
- New noise spectroscopy scheme:
We have developed a new method combining pulsed and continuous, phase modulated control to enhance noise spectroscopy, specifically for cases in which the noise spectrum is not monotonous (realistic for NV systems as well as others). We demonstrate the advantages of this new approach in terms of resolution, accuracy and bandwidth.
- Novel framework for Hamiltonian engineering of coupled spin ensembles:
We employed group theory to develop and unconventional methodology for Hamiltonian engineering, based on non-standard pulses derived from a larger symmetry group than usually considered (icosahedral vs. cubic). We show that our approach provides a general framework for Hamiltonian engineering in interacting spin-1/2 systems, and importantly allows for the simulation of any desired Hamiltonian, while also improving previous results of quantum sensing in interacting systems.
- Analytical analysis of superconducting couplers using a Green's function approach:
We have employed an analytical Green's function approach, based on related work developed in electrostatics, and have derived a closed functional form of the effect for simplified geometries. This unique theoretical framework is quite powerful, and its extension to more realistic geometries could shed new light into the physical processes underlying the enhanced coupling and allow for insightful optimization of the experimental system.
- New methods for NV charge initialization and spin readout using IR excitation and fluorescence:
We addressed the problem of NV readout SNR using an unconventional approach, looking to enhance the relatively weak IR fluorescence of the NV singlet transition (as opposed to the stronger visible fluorescence of the main triplet transition). Our method relies on the much narrower spectral bandwidth of the IR fluorescence, which allows for significant enhancement through carefully designed nano-photonic structures (photonic crystal cavity). We expect that this novel technique will significantly enhance the NV spin readout SNR, potentially to the level of single-shot readout.
- Based on these developments, we have pioneered and demonstrated a novel scheme for the measurement of radical concentrations. We have identified a charge-transfer process induced on shallow NVs by nearby radicals, which can then be measured through the NV charge state. This work, carried out in collaboration with the group of Uri Banin from the Hebrew University, achieved a sensitivity of 11 nM/sqrt(Hz).
We detail these methodologies below, based on the achievements described above:
- New technique for local, in-house electron irradiation using TEM:
We have used spatially localized irradiation based on in-house available TEM equipment, demonstrating improved NV concentrations in commonly available and implanted samples, without adversely affecting the NV coherence properties.
- New noise spectroscopy scheme:
We have developed a new method combining pulsed and continuous, phase modulated control to enhance noise spectroscopy, specifically for cases in which the noise spectrum is not monotonous (realistic for NV systems as well as others). We demonstrate the advantages of this new approach in terms of resolution, accuracy and bandwidth.
- Novel framework for Hamiltonian engineering of coupled spin ensembles:
We employed group theory to develop and unconventional methodology for Hamiltonian engineering, based on non-standard pulses derived from a larger symmetry group than usually considered (icosahedral vs. cubic). We show that our approach provides a general framework for Hamiltonian engineering in interacting spin-1/2 systems, and importantly allows for the simulation of any desired Hamiltonian, while also improving previous results of quantum sensing in interacting systems.
- Analytical analysis of superconducting couplers using a Green's function approach:
We have employed an analytical Green's function approach, based on related work developed in electrostatics, and have derived a closed functional form of the effect for simplified geometries. This unique theoretical framework is quite powerful, and its extension to more realistic geometries could shed new light into the physical processes underlying the enhanced coupling and allow for insightful optimization of the experimental system.
- New methods for NV charge initialization and spin readout using IR excitation and fluorescence:
We addressed the problem of NV readout SNR using an unconventional approach, looking to enhance the relatively weak IR fluorescence of the NV singlet transition (as opposed to the stronger visible fluorescence of the main triplet transition). Our method relies on the much narrower spectral bandwidth of the IR fluorescence, which allows for significant enhancement through carefully designed nano-photonic structures (photonic crystal cavity). We expect that this novel technique will significantly enhance the NV spin readout SNR, potentially to the level of single-shot readout.
- Based on these developments, we have pioneered and demonstrated a novel scheme for the measurement of radical concentrations. We have identified a charge-transfer process induced on shallow NVs by nearby radicals, which can then be measured through the NV charge state. This work, carried out in collaboration with the group of Uri Banin from the Hebrew University, achieved a sensitivity of 11 nM/sqrt(Hz).
I would consider the following as significant achievements beyond the state of the art:
- The development of a novel, general control scheme for interacting spin systems, based on the icosahedral symmetry group. This approach constitutes a breakthrough, as it goes beyond standard techniques, and the expansion to a higher symmetry group allows for complete control of quantum many-body spin systems, which was previously not attainable. This result is central to the project and its goals.
- The new scheme for radical sensing constitutes a breakthrough, as it enables high-resolution, high-sensitivity, in-situ characterization of radical concentration, which is otherwise not possible. This result was quite unexpected, and could have significant impact on varied fields, including the improvement of clean energy storage (addressing battery cell degradation) and the study of biological cellular stress effects.
- The development of a novel, general control scheme for interacting spin systems, based on the icosahedral symmetry group. This approach constitutes a breakthrough, as it goes beyond standard techniques, and the expansion to a higher symmetry group allows for complete control of quantum many-body spin systems, which was previously not attainable. This result is central to the project and its goals.
- The new scheme for radical sensing constitutes a breakthrough, as it enables high-resolution, high-sensitivity, in-situ characterization of radical concentration, which is otherwise not possible. This result was quite unexpected, and could have significant impact on varied fields, including the improvement of clean energy storage (addressing battery cell degradation) and the study of biological cellular stress effects.