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Journal articleSchwickert D, Przystawik A, Diaman D, et al., 2024,
Coupled electron-nuclear dynamics induced and monitored with femtosecond soft X-ray pulses in the amino acid glycine
, The Journal of Physical Chemistry A: Isolated Molecules, Clusters, Radicals, and Ions; Environmental Chemistry, Geochemistry, and Astrochemistry; Theory, Vol: 128, Pages: 989-995, ISSN: 1089-5639The coupling of electronic and nuclear motion in polyatomic molecules is at the heart of attochemistry. The molecular properties, transient structures, and reaction mechanism of these many-body quantum objects are defined on the level of electrons and ions by molecular wave functions and their coherent superposition, respectively. In the present contribution, we monitor nonadiabatic quantum wave packet dynamics during molecular charge motion by reconstructing both the oscillatory charge density distribution and the characteristic time-dependent nuclear configuration coordinate from time-resolved Auger electron spectroscopic data recorded in previous studies on glycine molecules [Schwickert et al. Sci. Adv. 2022, 8, eabn6848]. The electronic and nuclear motion on the femtosecond time scale was induced and probed in kinematically complete soft X-ray experiments at the FLASH free-electron laser facility. The detailed analysis of amplitude, instantaneous phase, and instantaneous frequency of the propagating many-body wave packet during its lifecycle provides unprecedented insight into dynamical processes beyond the Born-Oppenheimer approximation. We are confident that the refined experimental data evaluation helps to develop new theoretical tools to describe time-dependent molecular wave functions in complicated but ubiquitous non-Born-Oppenheimer photochemical conditions.
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Journal articlePetiziol F, Wimberger S, Eckardt A, et al., 2024,
Nonperturbative Floquet engineering of the toric-code Hamiltonian and its ground state
, PHYSICAL REVIEW B, Vol: 109, ISSN: 2469-9950 -
Journal articleBressanini G, Kwon H, Kim MS, 2024,
Gaussian boson sampling with click-counting detectors
, Physical Review A: Atomic, Molecular and Optical Physics, Vol: 109, ISSN: 1050-2947Gaussian boson sampling constitutes a prime candidate for an experimental demonstration of quantum advantage within reach with current technological capabilities. The original proposal employs photon-number-resolving detectors, however, these are not widely available. Nevertheless, inexpensive threshold detectors can be combined into a single click-counting detector to achieve approximate photon-number resolution. We investigate the problem of sampling from a general multimode Gaussian state using click-counting detectors and show that the probability of obtaining a given outcome is related to a matrix function which is dubbed as the Kensingtonian. We show how the Kensingtonian relates to the Torontonian and the Hafnian, thus bridging the gap between known Gaussian boson sampling variants. We then prove that, under standard complexity-theoretical conjectures, the model cannot be simulated efficiently.
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Journal articleFekete J, Joshi P, Barrett TJ, et al., 2024,
Quantum Gas-Enabled Direct Mapping of Active Current Density in Percolating Networks of Nanowires
, NANO LETTERS, Vol: 24, Pages: 1309-1315, ISSN: 1530-6984 -
Journal articleXu L, Zhou M, Tao R, et al., 2024,
Resource-Efficient Direct Characterization of General Density Matrix
, PHYSICAL REVIEW LETTERS, Vol: 132, ISSN: 0031-9007 -
Conference paperVanner MR, 2024,
Brillouin Optomechanics: Strong coupling, the lasing transition, and single-phonon-level operations
, ISSN: 0277-786XBackward Brillouin scattering in whispering-gallery-mode micro-resonators offers an exciting avenue to pursue both classical and quantum optomechanics applications. Our team—the Quantum Measurement Lab—together with our collaborators, are currently exploring and utilizing the favourable properties this platform affords for non-Gaussian motional state preparation of acoustic fields. In particular, the high acoustic frequencies, acoustic mode selectivity, and low optical absorption provide a promising route to overcome current hindrances within optomechanics. Some of our key recent results in this direction include: the observation of Brillouin optomechanical strong coupling, single-phonon addition and subtraction to a thermal state of the acoustic field, advancing the state-of-the-art of mechanical state tomography to observe the non-Gaussian states generated by single- and multi-phonon subtraction, studying the second-order coherence across the Brillouin lasing threshold, and enhancing sideband cooling via zero-photon detection. This talk will cover these results, what they enable, and the broader direction of our lab.
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Conference paperPodolsky V, Hepner S, Schipmann S, et al., 2024,
Characterization of a broad beam ion source converted into a high intensity deuterium beam
, ISSN: 1742-6588Avalanche Energy is developing deuterium ion beams for the Orbitron fusion device. For these and similar projects, modification of off-the-shelf high current ion sources enables affordable and rapidly accessible alternatives to custom-built systems. We have successfully operated the Veeco MARK I broad beam source on deuterium to create multi-keV energy ions. Directing this beam through a small aperture required carefully designed optics. Once a narrower beam was created, a faraday cup was used to measure the beam current and profile while a Thomson Parabola was developed to help understand the beam species and energy composition.
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Journal articleGarratt D, Matthews M, Marangos J, 2024,
Towards ultrafast soft X-ray spectroscopy of organic photovoltaic devices
, Structural Dynamics, Vol: 11, ISSN: 2329-7778Novel ultrafast x-ray sources based on high harmonic generation and at x-ray free electron lasers are opening up new opportunities to resolve complex ultrafast processes in condensed phase systems with exceptional temporal resolution and atomic site specificity. In this perspective, we present techniques for resolving charge localization, transfer, and separation processes in organic semiconductors and organic photovoltaic devices with time-resolved soft x-ray spectroscopy. We review recent results in ultrafast soft x-ray spectroscopy of these systems and discuss routes to overcome the technical challenges in performing time-resolved x-ray experiments on photosensitive materials with poor thermal conductivity and low pump intensity thresholds for nonlinear effects.
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Journal articleRöser D, Padilla-Castillo JE, Ohayon B, et al., 2024,
Hyperfine structure and isotope shifts of the (4s2) S0 1 →(4s4p) P1 1 transition in atomic zinc
, Physical Review A, Vol: 109, ISSN: 2469-9926We report absolute frequency, isotope shift, radiative lifetime, and hyperfine structure measurements of the (4s2)S01→(4s4p)P11 (213.8 nm) transition in Zn I using a cryogenic buffer gas beam. Laser-induced fluorescence is collected with two orthogonally oriented detectors to take advantage of differences in the emission pattern of the isotopes. This enables a clear distinction between isotopes whose resonances are otherwise unresolved, and a measurement of the Zn67 hyperfine structure parameters, A(Zn67)=20(2)MHz and B(Zn67)=10(5)MHz. We reference our frequency measurements to an ultralow expansion cavity and achieve an uncertainty at the level of 1 MHz, about 1 percent of the natural linewidth of the transition.
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Journal articleMa Y, Kim MS, 2024,
Limitations of probabilistic error cancellation for open dynamics beyond sampling overhead
, Physical Review A: Atomic, Molecular and Optical Physics, Vol: 109, ISSN: 1050-2947Quantum simulation of dynamics is an important goal in the noisy intermediate-scale quantum era, within which quantum error mitigation may be a viable path towards modifying or eliminating the effects of noise. Most studies on quantum error mitigation have focused on the resource cost due to its exponential scaling in the circuit depth. Methods such as probabilistic error cancellation rely on discretizing the evolution into finite time steps and applying the mitigation layer after each time step, modifying only the noise part without any Hamiltonian dependence. This may lead to Trotter-like errors in the simulation results even if the error mitigation is implemented ideally, which means that the number of samples is taken as infinite. Here we analyze the aforementioned errors which have been largely neglected before. We show that they are determined by the commutating relations between the superoperators of the unitary part, the device noise part, and the noise part of the open dynamics to be simulated. We include both digital quantum simulation and analog quantum simulation setups and consider defining the ideal error mitigation map both by exactly inverting the noise channel and by approximating it to first order in the time step. We use single-qubit toy models to numerically demonstrate our findings. Our results illustrate fundamental limitations of applying probabilistic error cancellation in a stepwise manner to continuous dynamics, thus motivating the investigations of truly time-continuous error cancellation methods.
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Journal articleBressanini G, Kwon H, Kim MS, 2024,
Gaussian boson sampling at finite temperature
, Physical Review A: Atomic, Molecular and Optical Physics, Vol: 109, ISSN: 1050-2947Gaussian boson sampling (GBS) is a promising candidate for an experimental demonstration of quantum advantage using photons. However, sufficiently large noise might hinder a GBS implementation from entering the regime where quantum speedup is achievable. Here, we investigate how thermal noise affects the classical intractability of generic quantum optical sampling experiments, GBS being a particular instance of the latter. We do so by establishing sufficient conditions for an efficient simulation to be feasible, expressed in the form of inequalities between the relevant parameters that characterize the system and its imperfections. We demonstrate that the addition of thermal noise—modeled by (passive) linear optical interaction between the system and a Markovian thermal bath—has the effect of tightening the constraints on the remaining noise parameters, required to show quantum advantage. Furthermore, we show that there exists a threshold temperature, under the assumption of a uniform loss rate, at which quantum sampling experiments become classically simulable, and provide an intuitive physical interpretation by relating this occurrence with the disappearance of the quantum state's nonclassical properties.
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Journal articlePetiziol F, Mintert F, Wimberger S, 2024,
Quantum control by effective counterdiabatic driving
, EPL, Vol: 145, ISSN: 0295-5075 -
Journal articleJun Park J, Baek K, Kim MS, et al., 2024,
T-depth-optimized quantum search with quantum data-access machine
, Quantum Science and Technology, Vol: 9, ISSN: 2058-9565Quantum search algorithms offer a remarkable advantage of quadraticreduction in query complexity using quantum superposition principle. However, howan actual architecture may access and handle the database in a quantum superposedstate has been largely unexplored so far; the quantum state of data was simply assumedto be prepared and accessed by a black-box operation—so-called oracle, even thoughthis process, if not appropriately designed, may adversely diminish the quantum queryadvantage. Here, we introduce an efficient quantum data-access process, dubbedas quantum data-access machine (QDAM), and present a general architecture forquantum search algorithm. We analyze the runtime of our algorithm in view of thefault-tolerant quantum computation (FTQC) consisting of logical qubits within aneffective quantum error correction code. Specifically, we introduce a measure involvingtwo computational complexities, i.e. quantum query and T-depth complexities, whichcan be critical to assess performance since the logical non-Clifford gates, such as theT (i.e., π/8 rotation) gate, are known to be costliest to implement in FTQC. Ouranalysis shows that for N searching data, a QDAM model exhibiting a logarithmic,i.e., O(log N), growth of the T-depth complexity can be constructed. Further analysisreveals that our QDAM-embedded quantum search requires O(√N × log N) runtimecost. Our study thus demonstrates that the quantum data search algorithm can trulyspeed up over classical approaches with the logarithmic T-depth QDAM as a keycomponent.
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Journal articleWenniger IMDB, Thomas SE, Maffei M, et al., 2023,
Experimental Analysis of Energy Transfers between a Quantum Emitter and Light Fields
, PHYSICAL REVIEW LETTERS, Vol: 131, ISSN: 0031-9007 -
Journal articleFrasinski LJ, 2023,
Cumulant mapping as the basis of multi-dimensional spectrometry (vol 24, pg 20776, 2022)
, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, Vol: 25, Pages: 32726-32726, ISSN: 1463-9076 -
Journal articleWiesinger M, Stuhlmann F, Bohman M, et al., 2023,
Trap-integrated fluorescence detection with silicon photomultipliers for sympathetic laser cooling in a cryogenic Penning trap
, REVIEW OF SCIENTIFIC INSTRUMENTS, Vol: 94, ISSN: 0034-6748 -
Journal articleZuo Z, Hanks M, Kim MS, 2023,
Coherent control of the causal order of entanglement distillation
, Physical Review A: Atomic, Molecular and Optical Physics, Vol: 108, ISSN: 1050-2947Indefinite causal order is an evolving field with potential involvement in quantum technologies. Here we propose and study one possible scenario of practical application in quantum communication: a compound entanglement distillation protocol that features two steps of a basic distillation protocol applied in a coherent superposition of two causal orders. This is achieved by using one faulty entangled pair to control-swap two others before a fourth pair is combined with the two swapped ones consecutively. As a result, the protocol distills the four faulty entangled states into one of a higher fidelity. Our protocol has a higher fidelity of distillation and probability of success for some input faulty pairs than conventional concatenations of the basic protocol that follow a definite distillation order. Our proposal shows the advantage of indefinite causal order in an application setting consistent with the requirements of quantum communication.
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Journal articleAhyoune S, Álvarez Melcón A, Arguedas Cuendis S, et al., 2023,
A proposal for a low-frequency axion search in the 1–2 μ eV range and below with the babyIAXO magnet
, Annalen der Physik, Vol: 535, ISSN: 0003-3804In the near future BabyIAXO will be the most powerful axion helioscope,relying on a custom-made magnet of two bores of 70 cm diameter and 10 mlong, with a total available magnetic volume of more than 7 m3. In thisdocument, it proposes and describe the implementation of low-frequencyaxion haloscope setups suitable for operation inside the BabyIAXO magnet.The RADES proposal has a potential sensitivity to the axion-photon couplingga𝜸 down to values corresponding to the KSVZ model, in the (currentlyunexplored) mass range between 1 and 2 𝛍 eV, after a total effective exposureof 440 days. This mass range is covered by the use of four differentlydimensioned 5-meter-long cavities, equipped with a tuning mechanism basedon inner turning plates. A setup like the one proposed will also allow anexploration of the same mass range for hidden photons coupled to photons.An additional complementary apparatus is proposed using LC circuits andexploring the low energy range (≈ 10−4 − 10−1 𝛍 eV). The setup includes acryostat and cooling system to cool down the BabyIAXO bore down to about 5K, as well as an appropriate low-noise signal amplification anddetection chain.
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Journal articleHo C, Wright S, Sauer B, et al., 2023,
Systematic errors arising from polarization imperfections in measurements of the electron’s electric dipole moment
, Physical Review Research, Vol: 5, ISSN: 2643-1564The electron’s electric dipole moment (eEDM) can be determined by polarizing the spin of an atom or a molecule and then measuring the spin precession frequency in an applied electric field. Radiation is used to polarize the spin and then analyze the precession angle, and the measurement is often sensitive to the polarization of this radiation. We show how systematic errors can arise when both the polarization of the radiation and the magnitude of the electric field are imperfectly controlled. We derive approximate analytical expressions for these errors, confirm their accuracy numerically, and show how they can be corrected empirically. We consider spin manipulation using single-photon pulses, Raman pulses, and Stimulated Raman Adiabatic Passage (STIRAP), and show that STIRAP provides better immunity to these systematic errors. An experimental study of these errors partly supports our findings but also reveals another potential error that is not captured by this analysis.
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Journal articleRudolph T, Virmani SS, 2023,
The two-qubit singlet/triplet measurement is universal for quantum computing given only maximally-mixed initial states
, Nature Communications, Vol: 14, ISSN: 2041-1723In order to delineate which minimalistic physical primitives can enable the full power of universal quantum computing, it has been fruitful to consider various measurement based architectures which reduce or eliminate the use of coherent unitary evolution, and also involve operations that are physically natural. In this context previous works had shown that the triplet-singlet measurement of two qubit angular momentum (or equivalently two qubit exchange symmetry) yields the power of quantum computation given access to a few additional different single qubit states or gates. However, Freedman, Hastings and Shokrian-Zini1 recently proposed a remarkable conjecture, called the ‘STP=BQP’ conjecture, which states that the two-qubit singlet/triplet measurement is quantum computationally universal given only an initial ensemble of maximally mixed single qubits. In this work we prove this conjecture. This provides a method for quantum computing that is fully rotationally symmetric (i.e. reference frame independent), using primitives that are physically very-accessible, naturally resilient to certain forms of error, and provably the simplest possible.
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Journal articleCryer-Jenkins EA, Enzian G, Freisem L, et al., 2023,
Second-order coherence across the Brillouin lasing threshold
, Optica, Vol: 10, Pages: 1432-1438, ISSN: 2334-2536Brillouin–Mandelstam scattering is one of the most accessible nonlinear optical phenomena and has been widely studied since its theoretical discovery one hundred years ago. The scattering mechanism is a three-wave-mixing process between two optical fields and one acoustic field and has found a broad range of applications spanning microscopy to ultra-narrow-linewidth lasers. Building on the success of utilizing this nonlinearity at a classical level, a rich avenue is now being opened to explore Brillouin scattering within the paradigm of quantum optics. Here, we take a key step in this direction by employing quantum optical techniques yet to be utilized for Brillouin scattering to characterize the second-order coherence of Stokes scattering across the Brillouin lasing threshold. We use a silica microsphere resonator and single-photon counters to observe the expected transition from bunched statistics of thermal light below the lasing threshold to Poissonian statistics of coherent light above the threshold. Notably, at powers approaching the lasing threshold, we also observe super-thermal statistics, which arise due to instability and a “flickering” in and out of lasing as the pump field is transiently depleted. The statistics observed across the transition, including the “flickering,” are a result of the full nonlinear three-wave-mixing process and cannot be captured by a linearized model. These measurements are in good agreement with numerical solutions of the three-wave Langevin equations and are well demarcated by analytical expressions for the instability and the lasing thresholds. These results demonstrate that applying second-order-coherence and photon-counting measurements to Brillouin scattering provides new methods to advance our understanding of Brillouin scattering itself and progress toward quantum-state preparation and characterization of acoustic modes.
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Journal articleMa Y, Hanks M, Kim MS, 2023,
Non-Pauli errors can be efficiently sampled in qudit surface codes
, Physical Review Letters, Vol: 131, ISSN: 0031-9007Surface codes are the most promising candidates for fault-tolerant quantum computation. Single qudit errors are typically modeled as Pauli operators, to which general errors are converted via randomizing methods. In this Letter, we quantify remaining correlations after syndrome measurement for a qudit 2D surface code subject to non-Pauli errors via loops on the lattice, using percolation theory. Below the error correction threshold, remaining correlations are sparse and locally constrained. Syndromes for qudit surface codes are therefore efficiently samplable for non-Pauli errors, independent of the exact forms of the error and decoder.
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Journal articleSmorra C, Abbass F, Schweitzer D, et al., 2023,
BASE-STEP: a transportable antiproton reservoir for fundamental interaction studies
, Review of Scientific Instruments, Vol: 94, ISSN: 0034-6748Currently, the world's only source of low-energy antiprotons is the AD/ELENA facility located at CERN. To date, all precision measurements on single antiprotons have been conducted at this facility and provide stringent tests of fundamental interactions and their symmetries. However, magnetic field fluctuations from the facility operation limit the precision of upcoming measurements. To overcome this limitation, we have designed the transportable antiproton trap system BASE-STEP to relocate antiprotons to laboratories with a calm magnetic environment. We anticipate that the transportable antiproton trap will facilitate enhanced tests of charge, parity, and time-reversal invariance with antiprotons and provide new experimental possibilities of using transported antiprotons and other accelerator-produced exotic ions. We present here the technical design of the transportable trap system. This includes the transportable superconducting magnet, the cryogenic inlay consisting of the trap stack and detection systems, and the differential pumping section to suppress the residual gas flow into the cryogenic trap chamber.
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Journal articleHutchison CDM, Baxter JM, Fitzpatrick A, et al., 2023,
Optical control of ultrafast structural dynamics in a fluorescent protein
, NATURE CHEMISTRY, ISSN: 1755-4330 -
Journal articleYu S, Zhong Z-P, Fang Y, et al., 2023,
A universal programmable Gaussian boson sampler for drug discovery
, NATURE COMPUTATIONAL SCIENCE -
Journal articleAlexander O, Barnard J, Larsen E, et al., 2023,
Observation of recollision-based high-harmonic generation in liquid isopropanol and the role of electron scattering
, Physical Review Research, ISSN: 2643-1564 -
Journal articleLatacz BM, Arndt BP, Devlin JA, et al., 2023,
Ultra-thin polymer foil cryogenic window for antiproton deceleration and storage
, REVIEW OF SCIENTIFIC INSTRUMENTS, Vol: 94, ISSN: 0034-6748 -
Journal articleSmith AWR, Paige AJ, Kim MS, 2023,
Faster variational quantum algorithms with quantum kernel-based surrogate models
, Quantum Science and Technology, Vol: 8, ISSN: 2058-9565We present a new optimization strategy for small-to-intermediate scale variational quantum algorithms (VQAs) on noisy near-term quantum processors which uses a Gaussian process surrogate model equipped with a classically-evaluated quantum kernel. VQAs are typically optimized using gradient-based approaches however these are difficult to implement on current noisy devices, requiring large numbers of objective function evaluations. Our approach shifts this computational burden onto the classical optimizer component of these hybrid algorithms, greatly reducing the number of quantum circuit evaluations required from the quantum processor. We focus on the variational quantum eigensolver (VQE) algorithm and demonstrate numerically that these surrogate models are particularly well suited to the algorithm's objective function. Next, we apply these models to both noiseless and noisy VQE simulations and show that they exhibit better performance than widely-used classical kernels in terms of final accuracy and convergence speed. Compared to the typically-used stochastic gradient-descent approach to VQAs, our quantum kernel-based approach is found to consistently achieve significantly higher accuracy while requiring less than an order of magnitude fewer quantum circuit executions. We analyze the performance of the quantum kernel-based models in terms of the kernels' induced feature spaces and explicitly construct their feature maps. Finally, we describe a scheme for approximating the best-performing quantum kernel using a classically-efficient tensor network representation of its input state and so provide a pathway for scaling this strategy to larger systems.
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Journal articleYu S, Zhong Z-P, Fang Y, et al., 2023,
A universal programmable Gaussian boson sampler for drug discovery.
, Nat Comput Sci, Vol: 3, Pages: 839-848Gaussian boson sampling (GBS) has the potential to solve complex graph problems, such as clique finding, which is relevant to drug discovery tasks. However, realizing the full benefits of quantum enhancements requires large-scale quantum hardware with universal programmability. Here we have developed a time-bin-encoded GBS photonic quantum processor that is universal, programmable and software-scalable. Our processor features freely adjustable squeezing parameters and can implement arbitrary unitary operations with a programmable interferometer. Leveraging our processor, we successfully executed clique finding on a 32-node graph, achieving approximately twice the success probability compared to classical sampling. As proof of concept, we implemented a versatile quantum drug discovery platform using this GBS processor, enabling molecular docking and RNA-folding prediction tasks. Our work achieves GBS circuitry with its universal and programmable architecture, advancing GBS toward use in real-world applications.
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Journal articleZeng X-D, Yang Y-Z, Guo N-J, et al., 2023,
Reflective dielectric cavity enhanced emission from hexagonal boron nitride spin defect arrays.
, Nanoscale, Vol: 15, Pages: 15000-15007Among the various kinds of spin defects in hexagonal boron nitride (hBN), the negatively charged boron vacancy (VB-) spin defect that can be site-specifically generated is undoubtedly a potential candidate for quantum sensing, but its low quantum efficiency restricts its practical applications. Here, we demonstrate a robust enhancement structure called reflective dielectric cavity (RDC) with advantages including easy on-chip integration, convenient processing, low cost and suitable broad-spectrum enhancement for VB- defects. In the experiment, we used a metal reflective layer under the hBN flakes, filled with a transition dielectric layer in the middle, and adjusted the thickness of the dielectric layer to achieve the best coupling between RDC and spin defects in hBN. A remarkable 11-fold enhancement in the fluorescence intensity of VB- spin defects in hBN flakes can be achieved. By designing the metal layer into a waveguide structure, high-contrast optically detected magnetic resonance (ODMR) signal (∼21%) can be obtained. The oxide layer of the RDC can be used as the integrated material to implement secondary processing of micro-nano photonic devices, which means that it can be combined with other enhancement structures to achieve stronger enhancement. This work has guiding significance for realizing the on-chip integration of spin defects in two-dimensional materials.
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