G. P. Berman, F. Borgonovi, G. Chapline, P. C. Hammel, V. I. Tsifrinovich
We simulate magnetic resonance force microscopy measurements of an entangled spin state. One of the entangled spins drives the resonant cantilever vibrations, while the other remote spin does not interact directly with the quasiclassical cantilever. The Schrödinger cat state of the cantilever reveals two possible outcomes of the measurement for both entangled spins.
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We propose a magnetic resonance force microscopy (MRFM)-based nuclear spin quantum computer using tellurium impurities in silicon. This approach to quantum computing combines the well-developed silicon technology with expected advances in MRFM.
We propose a nuclear spin quantum computer based on magnetic resonance force microscopy (MRFM). It is shown that an MRFM single-electron spin measurement provides three essential requirements for quantum computation in solids: (a) preparation of the ground state, (b) one- and two- qubit quantum logic gates, and (c) a measurement of the final state. The proposed quantum computer can operate at temperatures up to 1K.
Entangled sensors have been attracting a lot of attention recently because they can achieve the sensitivity beyond that of the classical sensors. To exploit entanglement as a resource, it is important to understand the effect of noise because the entangled state is fragile against noise. Here, we provide a Nuclear Magnetic Resonance (NMR) model of an entangled sensor under engineered noise: one can implement an entangled sensor under various noisy environments. In particular, we experimentally investigate the performance of the entangled sensor under the effect of time-inhomogeneous noisy envi…
We consider theoretically the novel technique in magnetic resonance force microscopy which is called ``oscillating cantilever-driven adiabatic reversals''. We present analytical and numerical analysis for the stationary cantilever vibrations in this technique. For reasonable values of parameters we estimate the resonant frequency shift as 6Hz per the Bohr magneton. We analyze also the regime of small oscillations of the paramagnetic moment near the transversal plane and the frequency shift of the damped cantilever vibrations.
We propose a simple model which describes the statistical properties of quantum jumps in a single-spin measurement using the oscillating cantilever-driven adiabatic reversals technique in magnetic resonance force microscopy. Our computer simulations based on this model predict the average time interval between two consecutive quantum jumps and the correlation time to be proportional to the characteristic time of the magnetic noise and inversely proportional to the square of the magnetic noise amplitude.
Sub-μm axial precision depth imaging with entangled two-colour Hong-Ou-Mandel microscopy
本文提出利用纠缠双光色 Hong-Ou-Mandel 干涉测量结合二维光栅扫描评估半透明样品厚度变化，通过调节纠缠光子对波长间隔主动控制轴向精度与动态范围，实现了亚微米级深度成像精度。
By choosing H nucleus in Carbon-13 labelled trichloroethylene as one qubit environment, and two C nuclei as a two-qubit system, we have simulated quantum decoherence when the system lies in an entangled state using nuclear magnetic resonance (NMR). Decoupling technique is used to trace over the environment degrees of freedom. Experimental results show agreements with the theoretical predictions. Our experiment scheme can be generalized to the case that environment is composed of multiple qubits.
We consider a simple version of a cyclic adiabatic inversion (CAI) technique in magnetic resonance force microscopy (MRFM). We study the problem: What component of the spin is measured in the CAI MRFM? We show that the non-destructive detection of the cantilever vibrations provides a measurement of the spin component along the effective magnetic field. This result is based on numerical simulations of the Hamiltonian dynamics (the Schrodinger equation) and the numerical solution of the master equation.
An exact analytical solution of the decaying wave function of two identical noninteracting particles, which are entangled by spatial symmetry, is used to analyze the effect of the resonance spectra in the propagation of the decaying probability density outside the interaction potential region. We find, using exactly solvable problems, that a usual approximation that considers the two resonance levels associated with the initial states, is affected substantially in the case of sharp high energy resonances by disrupting the pure exponential decaying regime exhibited by the two resonance level ap…
We study the effects of wave function collapses in the oscillating cantilever driven adiabatic reversals (OSCAR) magnetic resonance force microscopy (MRFM) technique. The quantum dynamics of the cantilever tip (CT) and the spin is analyzed and simulated taking into account the magnetic noise on the spin. The deviation of the spin from the direction of the effective magnetic field causes a measurable shift of the frequency of the CT oscillations. We show that the experimental study of this shift can reveal the information about the average time interval between the consecutive collapses of the …
The achievement of three-dimensional atomic resolution magnetic resonance microscopy remains one of the main challenges in the visualization of biological molecules. The prospects for single spin microscopy have come tantalizingly close due to the recent developments in sensitive instrumentation. Despite the single spin detection capability in systems of spatially well-isolated spins, the challenge that remains is the creation of conditions in space where only a single spin is resonant and detected in the presence of other spins in its natural dense spin environment. We present a nanomagnetic …
We study the resonance interaction between two entangled identical atoms coupled to a quantized scalar field vacuum, and accelerating between two mirrors. We show how radiative processes of the two-atom entangled state can be manipulated by the atomic configuration undergoing noninertial motion. Incorporating the Heisenberg picture with symmetric operator ordering, the vacuum fluctuation and the self-reaction contributions are distinguished. We evaluate the resonance energy shift and the relaxation rate of energy of the two atom system from the self-reaction contribution in the Heisenberg equa…
We simulated the quantum dynamics for magnetic resonance force microscopy (MRFM) in the oscillating cantilever-driven adiabatic reversals (OSCAR) technique. We estimated the frequency shift of the cantilever vibrations and demonstrated that this shift causes the formation of a Schrodinger cat state which has some similarities and differences from the conventional MRFM technique which uses cyclic adiabatic reversals of spins. The interaction of the cantilever with the environment is shown to quickly destroy the coherence between the two possible cantilever trajectories. We have shown that using…
A scheme for generating the maximally entangled mixed state of two atoms on-resonance asymmetrically coupled to a single mode optical cavity field is presented. The part frontier of both maximally entangled mixed states and maximal Bell violating mixed states can be approximately reached by the evolving reduced density matrix of two atoms if the ratio of coupling strengths of two atoms is appropriately controlled. It is also shown that exchange symmetry of global maximal concurrence is broken if and only if coupling strength ratio lies between $\frac{\sqrt{3}}{3}$ and $\sqrt{3}$ for the case o…
Demonstration of Quantum Polarization Microscopy using an Entangled-Photon Source
本文实验演示了一种利用纠缠信号光子与闲置光子符合计数构建图像对比度的量子偏振显微术，并通过偏振切换揭示不同热态的二阶自相关差异。
Adaptive Optical Imaging with Entangled Photons
针对无标记显微术中传统自适应光学依赖导星和特定优化指标的问题，本文提出利用纠缠光子相关性直接校正PSF的无导星方法，并在生物样品明场成像中证明其对散焦等像差的校正优势。
Quantitative phase gradient microscopy with spatially entangled photons
本研究提出了一种基于空间纠缠光子的新型定量相位梯度显微镜技术，实现了高分辨率和高灵敏度的相位与振幅成像，突破了传统方法的限制。
We consider the resonance interaction energy between two identical entangled atoms, where one is in the excited state and the other in the ground state. They interact with the quantum electromagnetic field in the vacuum state and are placed in a photonic-bandgap environment with a dispersion relation quadratic near the gap edge and linear for low frequencies, while the atomic transition frequency is assumed to be inside the photonic gap and near its lower edge. This problem is strictly related to the coherent resonant energy transfer between atoms in external environments. The analysis involve…
Single-spin detection is one of the important challenges facing the development of several new technologies, e.g. single-spin transistors and solid-state quantum computation. Magnetic resonance force microscopy with a cyclic adiabatic inversion, which utilizes a cantilever oscillations driven by a single spin, is a promising technique to solve this problem. We have studied the quantum dynamics of a single spin interacting with a quasiclassical cantilever. It was found that in a similar fashion to the Stern-Gerlach interferometer the quantum dynamics generates a quantum superposition of two qua…
A requirement for many quantum computation schemes is the ability to measure single spins. This paper examines one proposed scheme: magnetic resonance force microscopy, including the effects of thermal noise and back-action from monitoring. We derive a simplified equation using the adiabatic approximation, and produce a stochastic pure state unraveling which is useful for numerical simulations.
In single spin Magnetic Resonance Force Microscopy (MRFM), the objective is to detect the presence of an electron (or nuclear) spin in a sample volume by measuring spin-induced attonewton forces using a micromachined cantilever. In the OSCAR method of single spin MRFM, the spins are manipulated by an external rf field to produce small periodic deviations in the resonant frequency of the cantilever. These deviations can be detected by frequency demodulation followed by conventional amplitude or energy detection. In this paper, we present an alternative to these detection methods, based on optim…
The resonance fluorescence from regular atomic systems is shown to represent a continuous source of non-Gaussian entangled radiation propagating in two different directions. For a single atom entanglement occurs under the same conditions as squeezing. For more atoms, the entanglement can be more robust against dephasing than squeezing, hence providing a useful continuous source for various applications of entangled radiation.
Entangled quantum states are an important element of quantum information techniques. We determine the requirements for states of quadrupolar nuclei with spins >1/2 to be entangled. It was shown that entanglement is achieved at low temperature by applying a magnetic field to a quadrupolar nuclei possess quadrupole moments, which interacts with the electricfield gradient produced by the charge distribution in their surroundings.
We investigate the resonance quadrupole-quadrupole interaction between two entangled gravitationally polarizable objects induced by a bath of fluctuating quantum gravitational fields in vacuum in the framework of linearized quantum gravity. Our result shows that, the interaction energy behaves as $r^{-5}$ in the near regime, and oscillates with a decreasing amplitude proportional to $r^{-1}$ in the far regime, where $r$ is the distance between the two objects. Compared to the case when the two objects are in their ground states, the quantum gravitational interaction is significantly enhanced w…
The spin state of two magnetically inequivalent protons in contiguous atoms of a molecule becomes entangeled by the indirect spin-spin interaction (j-coupling). The degree of entanglement oscillates at the beat frequency resulting from the splitting of a degeneracy. This beating is manifest in NMR spectroscopy as an envelope of the transverse magnetization and should be visible in the free induction decay signal. The period (approximately 1 sec) is long enough for interference between the linear dynamics and collapse of the wave-function induced by a Stern-Gerlach inhomogeneity to significantl…
Unraveling spin entanglement using quantum gates with scanning tunneling microscopy-driven electron spin resonance
利用ESR-STM实现固态平台中双量子比特纠缠态的确定性生成，展示了其在量子电路和纠缠态工程中的潜力。
Enhancement of broadband entangled two-photon absorption by resonant spectral phase flips
本文研究在宽带纠缠双光子吸收中引入单光子频谱相位翻转，通过扫描翻转频率定位中间共振，并利用共振色散虚部显著增强TPA速率，为低频谱区相位敏感光谱提供新方法。
We have studied theoretically magnetic resonance force microscopy (MRFM) with a high frequency nanomechanical cantilever when the cantilever frequency matches the resonant frequency of a single electron spin. Our estimations show that in this scenario the relative frequency shift of the cantilever can be much greater than the record MRFM frequency shift achieved in experiments with a single spin detection. Experimental realization of our proposal could open the way for fast detection of a single electron spin and even for detection of a single nuclear spin.
Magnetic Resonance Force Microscopy (MRFM) is a powerful technique to detect a small number of spins that relies on force-detection by an ultrasoft magnetically tipped cantilever and selective magnetic resonance manipulation of the spins. MRFM would greatly benefit from ultralow temperature operation, because of lower thermomechanical noise and increased thermal spin polarization. Here, we demonstrate MRFM operation at temperatures as low as 30 mK, thanks to a recently developed SQUID-based cantilever detection technique which avoids cantilever overheating. In our experiment, we detect danglin…
We explore the three-particle spin model of an $S_{1}=\frac{1}{2}$ particle (e.g. a stationary electron) interacting with two spin-coupled $S_{\text{2,3}}$ particles with exchange coupling and magnetic anisotropy. We find that in the case of $S_{2,3}=1$ particles, the coupled particle entanglement states can be prepared, controlled, and read by the $S_{1}$ particle. We also find that for particular resonance conditions of the magnetic anisotropy strength $D$ and exchange coupling strength $J$, the entanglement state switching behavior is maximized and is robust against a range of anisotropic a…
Spin Squeezing in Electron Microscopy
本文从理论上证明基于纠缠的自旋压缩可提升电子显微镜信噪比，通过电子-电子库仑相互作用和量子非破坏测量生成纠缠态，连接了量子计量学与电子干涉测量领域。
A quantum dot strongly coupled to a photonic crystal has been recently proposed as a source of entangled photon pairs [R. Johne et al., Phys. Rev. Lett. 100, 240404 (2008)]. The biexction decay via intermediate polariton states can be used to overcome the natural splitting between the exciton states coupled to the horizontally and vertically polarized light modes, so that high degrees of entanglement can be expected. We investigate theoretically the features of realistic dot-cavity systems, including the effect of the different oscillator strength of excitons resonances coupled to the differen…
Inspired by the unique nonclassical character of two-photon interactions induced by entangled photons, we develop a new comprehensive Förster-type formulation for entangled two-photon resonance energy transfer (E2P-RET) mediated by inhomogeneous, dispersive and absorptive media with any space-dependent and frequency-dependent dielectric function and with any size of donor/acceptor. In our theoretical framework, two uncoupled particles are jointly excited by the temporally entangled field associated with two virtual photons that are produced by three-level radiative cascade decay in a donor par…
Experimental Upper Bounds for Resonance-Enhanced Entangled Two-Photon Absorption Cross Section of Indocyanine Green
本研究首次探究有机染料吲哚菁绿的共振增强纠缠双光子吸收，测得其截面实验上限，同时首次测得其经典共振增强双光子吸收截面，发现共振中间态未显著增强该分子的双光子过程。
Entangled Two-Photon Absorption in Cesium Atoms and the Limitations of the Far-Off-Resonance Approximation
研究铯原子中纠缠双光子吸收（ETPA）过程，通过考虑中间态和退相干效应，比较有无远失谐近似下的截面，发现无近似时增强因子可达~500，揭示了近似在计算ETPA截面时的局限性。
Computational aberration-retrieval with entangled photons
本文提出利用纠缠光子对的空间相关性直接反演像差的自适应光学策略，以二阶相关函数为度量，仅需少量测量即可确定校正，无需图像反馈或迭代优化，为量子增强显微镜提供高效新框架。
Optical Widefield Nuclear Magnetic Resonance Microscopy
本研究利用金刚石NV中心将核磁共振信号转为光学信号，由高速相机捕获，实现约10微米分辨率、235×150微米区域的宽场NMR成像，每个像素记录完整谱信息，融合光学与NMR技术推动多领域成像应用。
We employ a quantum defect theory framework to provide a detailed analysis of the interplay between a magnetic Feshbach resonance and a shape resonance in cold collisions of ultracold $\rm ^{87}Rb$ atoms as captured in recent experiments using a laser-based collider [Phys. Rev. Research 3, 033209 (2021)]. By exerting control over a parameter space spanned by both collision energy and magnetic field, the width of a Feshbach resonance can be tuned over several orders of magnitude. We apply a quantum defect theory specialized for ultracold atomic collisions to fully describe of the experimental o…
We discuss details of the preparation and detection of entangled electron-nuclear spin states in 15N:C60 together with a quantitative evaluation of the complete density matrix. All four Bell states of a two qubit subsystem were analyzed. In addition we find a quantum critical temperature of Tq = 7.73 K for this system at an electron spin resonance frequency of 95 GHz.
A proposal for a scalable, solid-state implementation of a quantum computer is presented. Qubits are fluorine nuclear spins in a solid crystal of fluorapatite [Ca_5 F(PO_4)_3] with resonant frequencies separated by a large field gradient. Quantum logic is accomplished using nuclear-nuclear dipolar couplings with decoupling and selective recoupling RF pulse sequences. Magnetic resonance force microscopy is used for readout. As many as 300 qubits can be implemented in the laboratory extremes of T=10 mK and B_0=20 T with the existing sensitivity of force microscopy.
Theory of Electron Spin Resonance Scanning Tunneling Microscopy: The First Decade
综述ESR-STM技术十年进展，探讨电场驱动自旋共振的机制（Heisenberg交换、Kondo散射、Anderson杂质模型），验证理论预测，并讨论相干多自旋控制及电子-核自旋耦合系统的应用。
We experimentally demonstrate precision addressing of single quantum emitters by combined optical microscopy and spin resonance techniques. To this end we utilize nitrogen-vacancy (NV) color centers in diamond confined within a few ten nanometers as individually resolvable quantum systems. By developing a stochastic optical reconstruction microscopy (STORM) technique for NV centers we are able to simultaneously perform sub diffraction-limit imaging and optically detected spin resonance (ODMR) measurements on NV spins. This allows the assignment of spin resonance spectra to individual NV center…
Searching for axion dark matter with magnetic resonance force microscopy
利用磁共振力显微镜在1GHz附近探测轴子暗物质，通过优化泵浦场和磁场参数以提高检测灵敏度和限制轴子质量。
A Pulsed Live-Cell Quantum Microscope for Entangled Solid State and Biological Qubits
研究将生物量子比特与固态自旋基量子比特结合于同一显微镜平台，通过脉冲量子显微镜实现对活细胞中两种量子比特的量子态同时操纵，为活细胞量子传感带来新机遇。
In two-qubit gates activated by microwave pulses, by turning pulse on or off, the state of qubits are swapped between entangled or idle modes. In either mode, the presence of stray couplings makes qubits accumulate coherent phase error. However, the error rates in the two modes differ because qubits carry different stray coupling strengths in each mode; therefore, eliminating stray coupling from one mode does not remove it from the other. We propose to combine such a gate with a tunable coupler and show that both idle and entangled qubits can become free from stray couplings. This significantl…
Heisenberg Scaling Quantum Microscopy: Experiment and Theory
本文提出平衡光程的符合量子显微镜（QMC），实现海森堡极限下2倍超分辨、抗杂散光155倍，显著提升速度与对比度噪声比，推动癌细胞非破坏性生物成像。
We perform full time resolved tomographic measurements of the polarization state of pairs of photons emitted during the radiative cascade of the confined biexciton in a semiconductor quantum dot. The biexciton was deterministically initiated using a $π$-area pulse into the biexciton two-photon absorption resonance. Our measurements demonstrate that the polarization states of the emitted photon pair are maximally entangled. We show that the measured degree of entanglement depends solely on the temporal resolution by which the time difference between the emissions of the photon pair is determine…
We use Nuclear Magnetic Resonance (NMR) to experimentally generate a bound entangled (more precisely: pseudo bound entangled) state, i.e. a quantum state which is non-distillable but nevertheless entangled. Our quantum system consists of three qubits. We characterize the produced state via state tomography to show that the created state has a positive partial transposition with respect to any bipartite splitting, and we use a witness operator to prove its entanglement.
Entanglement in Resonance Fluorescence
提出基于共振荧光的新型纠缠光子源，利用强失谐激光驱动二能级系统卫星峰发射真空与Bell态叠加的光子对，可按需优化纠缠度，并成功使极化激元系统达到最大纠缠稳态。
Quantum dot spin valves are characterized by exchange fields which induce spin precession and generate current spin resonances even in absence of spin splitting. Analogous effects have been studied in double quantum dots, in which the orbital degree of freedom, the pseudospin, replaces the spin in the valve configuration. We generalize, now, this setup to allow for arbitrary spin and orbital polarization of the leads, thus obtaining an even richer variety of current resonances, stemming from the precession dynamics of entangled spin and pseudospin. We observe for both vectors a delicate interp…
Enhanced quantum emission from a topological Floquet resonance
本研究利用非磁性可调谐反常Floquet绝缘体，通过自发四波混频增强纠缠光子对产生，验证了非经典性与时间-能量纠缠，为鲁棒量子源提供新途径。
Two-photon excited fluorescence (TPEF) is a standard technique in modern microscopy but still affected by photo-damage of the probe. It was proposed that TPEF can be enhanced by using entangled photons, but has proven to be challenging. Recently it was shown that some features of entangled photons can be mimicked with thermal light, which finds application in ghost imaging, sub-wavelength lithography and metrology. Here, we utilize true thermal light from a super-luminescence diode to demonstrate enhanced TPEF compared to coherent light using two common fluorophores and luminescent quantum dot…
On the interpretation of Hahn echo measurements in electron spin resonance scanning tunneling microscopy
本文研究了电子自旋共振扫描隧道显微镜中Hahn回波测量的解释问题，指出RF电压导致的隧道电子影响了回波信号的相干性，并提出通过调整延迟时间以确保信号的相干性。
Electron spin resonance with scanning tunneling microscopy: a tool for an on-surface quantum platform of identical qubits
本文综述 ESR-STM 在表面原子与分子自旋量子比特中的原理、单自旋寻址、相干操控、读出及多量子比特逻辑门实现，表明其是构建原子尺度量子电路的重要平台。
We consider the time-dependent resonance interaction energy between two identical atoms, one in the ground state and the other in an excited state, and interacting with the vacuum electromagnetic field, during a nonequilibrium situation such as the dynamical atomic self-dressing process. We suppose the two atoms prepared in a correlated, symmetric or antisymmetric, state. Since the atoms start from a nonequilibrium conditions, their interaction energy is time dependent. We obtain, at second order in the atom-field coupling, an analytic expression for the time-dependent resonance interaction en…
Quantum-enhanced second harmonic generation beyond the photon pairs regime
本研究通过实验和理论验证，在超过传统阈值的高强度下仍能实现量子增强的双光子过程，展示了其在实际应用中的潜力。
Spin Resonance Spectroscopy with an Electron Microscope
本文提出一种基于微波泵浦场和电子探针、专为电子显微镜设计的泵浦-探测自旋共振光谱方法，可利用透射电镜探测极小相移，实现纳米尺度自旋动力学的状态选择性观测及自旋系统环境的间接测量。
We provide an exact solution of the scattering problem for the potentials of the form $v(x,y)=χ_a(x)[v_0(x)+ v_1(x)e^{iαy}]$, where $χ_a(x):=1$ for $x\in[0,a]$, $χ_a(x):=0$ for $x\notin[0,a]$, $v_j(x)$ are real or complex-valued functions, $χ_a(x)v_0(x)$ is an exactly solvable scattering potential in one dimension, and $α$ is a positive real parameter.If $α$ exceeds the wavenumber $k$ of the incident wave, the scattered wave does not depend on the choice of $v_1(x)$. In particular, $v(x,y)$ is invisible if $v_0(x)=0$ and $k<α$. For $k>α$ and $v_1(x)\neq 0$, the scattered wave consists of a fin…
We show unusual cooperative two-photon resonance between two-modes of field inside a photonic crystal cavity. The two-photon resonance occurs when two off resonant quantum dots emit one photon in each cavity mode and de-excite simultaneously. In the presence of phonon coupling the conditions for two-photon resonance change significantly. Using such two-photon two-mode interaction we propose to generate entangled state of two qutrits. The basis of a qutrit are formed by the state of the cavity mode containing $0$, $1$ and $2$ photons. We also discuss effect of phonon coupling on negativity of t…
Local magnetic resonance of scalar spin chirality
本研究针对具有标量自旋手征的量子态轨道磁矩无法直接测量的问题，提出利用局域驱动打破循环对称性激活手征性改变跃迁的方法，通过Lindblad模拟在多种自旋平台上验证了可实验观测的特征信号，为直接测量该轨道磁矩提供了途径。
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