Stefano Mancini, Sougato Bose
We propose the use of ponderomotive forces to entangle the motions of different atoms. Two situations are analyzed: one where the atoms belong to the same optical cavity and interact with the same radiation field mode; the other where each atom is placed in own optical cavity and the output field of one cavity enters the other.
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Accessing distinctly quantum aspects of the interaction between light and the position of a mechanical object has been an outstanding challenge to cavity-optomechanical systems. Only cold-atom implementations of cavity optomechanics have indicated effects of the quantum fluctuations in the optical radiation pressure force. Here we use such a system, in which quantum photon-number fluctuations significantly drive the center of mass of an atomic ensemble inside a Fabry-Perot cavity. We show that the optomechanical response both amplifies and ponderomotively squeezes the quantum light field. We a…
Entangling two qudits of arbitrary dimension through light-atomic Faraday interaction
本研究针对携带轨道角动量的光场态与原子集体自旋相干态编码的两个任意维度量子比特，提出基于两次法拉第相互作用及正交分量旋转的协议生成多种纠缠操作，且均可表示为d维SWAP门的有理幂次，并计算了不同维度与纠缠能力下的变换概率。
We propose an experimentally feasible scheme to generate Greenberger-Horne-Zeilinger (GHZ) type of maximal entanglement between many atomic ensembles based on laser manipulation and single-photon detection. The scheme, with inherent fault tolerance to the dominant noise and efficient scaling of the efficiency with the number of ensembles, allows to maximally entangle many atomic ensemble within the reach of current technology. Such a maximum entanglement of many ensembles has wide applications in demonstration of quantum nonlocality, high-precision spectroscopy, and quantum information process…
Entangling power of Anti-Jaynes-Cummings model and its efficiency to encode information in atomic system
本研究探讨Anti-Jaynes-Cummings Model在两原子Ising相互作用系统中生成量子纠缠的能力，证明其适合作为信息编码的量子信道，且通过调节相互作用参数可提升concurrence与信道容量。
Entangling Atomic Quantum Memories Using High-Order Modulated Coherent States
本研究提出利用高阶调制相干态和优化POVM测量，在原子量子存储器间实现每模式多个纠缠比特的高效分发，显著超越传统协议。
Spatiotemporal control of entangling gates on atomic N-qubit systems
本文提出一种包含脉冲时空参数的优化方法，用于原子N量子比特系统纠缠门制备，通过增强偶极阻塞可提速两个数量级，并评估了原子邻近度、几何结构及能量需求，最后按门机制分类最优协议。
We discuss the generation of two-atom entanglement inside a resonant microcavity under stimulated emission (STE) interaction. The amount of entanglement is shown based on different atomic initial state. For each kind of intial state, we obtain the entanglement period and the entanglement critical point, which are found to deeply depend on driving field density. In case of atomic state $| ee >$, the entanglement can be induced due to STE. In case of atomic state $| eg >$, there is a competition between driving field indued entanglement and STE induced entanglement. When two atoms are initially …
We first devise a scheme to perform a universal entangling gate via controlled collisions between pairs of atomic qubits trapped with optical tweezers. Second, we present a modification to this scheme to allow the preparation of atomic Bell pairs via selective excitation, suitable for quantum information processing applications that do not require universality. Both these schemes are enabled by the inherent symmetries of identical composite particles, as originally proposed by Hayes et al. Our scheme provides a technique for producing weighted graph states, entangled resources for quantum comm…
We demonstrate theoretically a scheme for cluster state generation, based on atomic ensembles and the dipole blockade mechanism. In the protocol, atomic ensembles serve as single qubit systems. Therefore, we review single-qubit operations on qubit defined as collective states of atomic ensemble. Our entangling protocol requires nearly identical single-photon sources, one ultra-cold ensemble per physical qubit, and regular photodetectors. The general entangling procedure is presented, as well as a procedure that generates in a single step Q-qubit GHZ states with success probability p_success ~ …
We describe a simple entangling principle based on the scattering of photons off single emitters in one-dimensional waveguides (or extremely-lossy cavities). The scheme can be applied to photonic qubits encoded in polarization or time-bin, and features a filtering mechanism that works effectively as a built-in error-correction directive. This automatically maps imperfections from weak couplings, atomic decay into undesired modes, frequency mismatches, or finite bandwidths of the incident photonic pulses, into heralded losses instead of infidelities. The scheme is thus adequate for high-fidelit…
In this paper we discuss four different proposals of entangling atomic states of particles which have never interacted. The experimental realization proposed makes use of the interaction of Rydberg atoms with a micromaser cavity prepared in either a coherent state or in a superposition of the zero and one field Fock states. We consider atoms in either a three-level cascade or lambda configuration
We study a string of neutral atoms with nearest neighbor interaction in a 1D beam splitter configuration, where the longitudinal motion is controlled by a moving optical lattice potential. The dynamics of the atoms crossing the beam splitter maps to a 1D spin model with controllable time dependent parameters, which allows the creation of maximally entangled states of atoms by crossing a quantum phase transition. Furthermore, we show that this system realizes protected quantum memory, and we discuss the implementation of one- and two-qubit gates in this setup.
We present a new scheme for cluster states generation based on atomic ensembles and the dipole blockade mechanism. The protocol requires identical single photon sources, one ensemble per physical qubit, and regular photodetectors. The general entangling procedure is presented, as well as a procedure that generates Q-qubit GHZ states with probability p ~ eta^{Q/2}, where eta is the combined detection and source efficiency. This is significantly more efficient than any known robust probabilistic entangling operation. The GHZ states form the basic building block for universal cluster states - a r…
We propose and analyse the use of a three-well Bose-Hubbard model for the creation of two spatially separated entangled atomic samples. Our three wells are in a linear configuration, with all atoms initially in the middle well, which gives some spatial separation of the two end wells. The evolution from the initial quantum state allows for the development of entanglement between the atomic modes in the two end wells. Using inseparability criteria developed by Hillery and Zubairy, we show how the detected entanglement is time dependent, oscillating with the well occupations. We suggest and anal…
We derive an analytical approximate solution of the time-dependent state vector in terms of material Bell states and coherent states of the field for a generalized two-atom Tavis-Cummings model with nonlinear intensity dependent matter-field interaction. Using this solution, we obtain simple expressions for the atomic concurrence and purity in order to study the entanglement in the system at specific interaction times. We show how to implement entangling atomic operations through measurement of the field. We illustrate how these operations can lead to a complete Bell measurement. Furthermore, …
A scheme is proposed here to achieve swapping and entangling of photonic and atomic qubits with high fidelity. The mechanism is based on the scattering of a single photon from a $Λ$-type three-level atom. The evolution of the coupled system is analyzed by projecting the quantum state onto a `bright' and a `dark' state. Quantum interference of these two states, which is determined by a frequency-dependent phase angle, can be exploited to perform various two-qubit transformations. It is remarkable that the probability of success of such transformations can approach unity in the strong coupling c…
Arrays of qubits encoded in the ground-state manifold of neutral atoms trapped in optical (or magnetic) lattices appear to be a promising platform for the realization of a scalable quantum computer. Two-qubit conditional gates between nearest-neighbor qubits in the array can be implemented by exploiting the Rydberg blockade mechanism, as was shown by D. Jaksch et al. [Phys. Rev. Lett. 85, 2208 (2000)]. However, the energy shift due to dipole-dipole interactions causing the blockade falls off rapidly with the interatomic distance and protocols based on direct Rydberg blockade typically fail to …
We propose a method for entangling a system of two-level atoms in photonic crystals. The atoms are assumed to move in void regions of a photonic crystal. The interaction between the atoms is mediated either via a defect mode or via resonant dipole-dipole interaction. We show that these interactions can produce pure entangled atomic states. We analyze the problem with parameters typical for currently existing photonic crystals and Rydberg atoms. We show that the atoms can emerge from photonic crystals in entangled states. Depending on the linear dimensions of the crystal and on their velocity o…
We propose an optical scheme for generating entanglement between co-trapped identical or dissimilar alkaline earth atomic ions ($^{40}\text{Ca}^+$, $^{88}\text{Sr}^+$, $^{138}\text{Ba}^+$, $^{226}\text{Ra}^+$) which exhibits fundamental error rates below $10^{-4}$ and can be implemented with a broad range of laser wavelengths spanning from ultraviolet to infrared. We also discuss straightforward extensions of this technique to include the two lightest Group-2 ions ($\text{Be}^+$, $\text{Mg}^+$) for multispecies entanglement. The key elements of this wavelength-insensitive geometric phase gate …
Controlling quantum entanglement between parts of a many-body system is the key to unlocking the power of quantum information processing for applications such as quantum computation, high-precision sensing, and simulation of many-body physics. Spin degrees of freedom of ultracold neutral atoms in their ground electronic state provide a natural platform given their long coherence times and our ability to control them with magneto-optical fields, but creating strong coherent coupling between spins has been challenging. We demonstrate a Rydberg-dressed ground-state blockade that provides a strong…
Fast nuclear-spin entangling gates compatible with large-scale atomic arrays
本研究提出了一种通过单个全局激光脉冲实现高保真度核自旋纠缠门的方法，适用于大规模原子阵列，通过增大Rabi频率缓解退相干问题。
Floquet geometric entangling gates in ground-state manifolds of Rydberg atoms
提出利用Floquet理论在Rydberg原子基态流形中构建容错两比特纠缠门，通过周期性调制Rabi频率实现高保真度与高鲁棒性，且比Rydberg态编码更具实用性。
We study three independent pairs of Jaynes-Cummings systems such that two atoms might be correlated with each other but the third atom is uncorrelated with rest. We investigate the conditions under which these uncorrelated three atoms may become genuinely entangled. We find that this task is impossible if the cavity interacting with uncorrelated atom share classical correlations with any other cavity. We observe that atomic state can become genuine multipartite entangled, at least if the cavity with uncorrelated atom, is highly entangled with any other cavity. This is an interesting and non-tr…
We investigate the procedure of Schmidt modes extraction in systems with continuous variables. An algorithm based on singular value matrix decomposition is applied to the study of entanglement in an "atom-photon" system with spontaneous radiation. Also, this algorithm is applied to the study of a bi-photon system with spontaneous parametric down conversion with type-II phase matching for broadband pump. We demonstrate that dynamic properties of entangled states in an atom-photon system with spontaneous radiation are defined by a parameter equal to the product of the fine structure constant and…
Hybrid atom-photon entangling gates via Gaussian soft control
提出基于高斯软控制的超导共面波导谐振器原子-微波光子受控Z门方案，通过高斯调制辅助场增强强耦合并提升门对参数偏差和能级移动的鲁棒性。
Finding, mapping and classifying optimal protocols for two-qubit entangling gates
本文基于量子路径机制分析并结合脉冲的时空优化，刻画、比较和分类中性原子 Rydberg 体系中双量子比特纠缠门的最优协议。
Scalable and efficient quantum computation with photonic qubits requires (i) deterministic sources of single-photons, (ii) giant nonlinearities capable of entangling pairs of photons, and (iii) reliable single-photon detectors. In addition, an optical quantum computer would need a robust reversible photon storage devise. Here we discuss several related techniques, based on the coherent manipulation of atomic ensembles in the regime of electromagnetically induced transparency, that are capable of implementing all of the above prerequisites for deterministic optical quantum computation with sing…
Entangling ferrimagnetic magnons with an atomic ensemble via opto-magnomechanics
本文提出在YIG晶体中利用光磁力学构型，通过光力与磁力冷却及参量下转换的协同作用，实现原子系综与磁振子的稳态宏观纠缠，并进一步展示原子、磁振子和声子的真正三体纠缠。
We study a means of creating multiparticle entanglement of neutral atoms using pairwise controlled dipole-dipole interactions in a three dimensional optical lattice. For tightly trapped atoms the dipolar interaction energy can be much larger than the photon scattering rate, and substantial coherent evolution of the two-atom state can be achieved before decoherence occurs. Excitation of the dipoles can be made conditional on the atomic states, allowing for deterministic generation of entanglement. We derive selection rules and a figure-of-merit for the dipole-dipole interaction matrix elements,…
We propose a scheme for entangling two field modes in two high-Q optical cavities. Making use of a virtual two-photon process, our scheme achieves maximally entangled states without any real transitions of atomic internal states, hence it is immune to the atomic decay.
Entangling quantum logic gates in neutral atoms via the microwave-driven spin-flip blockade
针对中性原子量子比特，本文提出利用Rydberg缀饰辅助态和微波驱动自旋翻转阻塞实现高保真两量子比特纠缠门，并证明中等阻塞区域可提升速度、降低衰减且增强抗噪性。
We demonstrate the use of an optical frequency comb to coherently control and entangle atomic qubits. A train of off-resonant ultrafast laser pulses is used to efficiently and coherently transfer population between electronic and vibrational states of trapped atomic ions and implement an entangling quantum logic gate with high fidelity. This technique can be extended to the high field regime where operations can be performed faster than the trap frequency. This general approach can be applied to more complex quantum systems, such as large collections of interacting atoms or molecules.
We discuss the creation of entanglement between two two-level atoms in the dissipative process of spontaneous emission. It is shown that spontaneous emission can lead to a transient entanglement between the atoms even if the atoms were prepared initially in an unentangled state. The amount of entanglement created in the system is quantified by using two different measures: concurrence and negativity. We find analytical formulas for the evolution of concurrence and negativity in the system. We also find the analytical relation between the two measures of entanglement. The system consists of two…
We study a scheme for entangling two-level atoms located close to the surface of a dielectric microsphere. The effect is based on medium-assisted spontaneous decay, rigorously taking into account dispersive and absorptive properties of the microsphere. We show that even in the weak-coupling regime, where the Markov approximation applies, entanglement up to 0.35 ebits between two atoms can be created. However, larger entanglement and violation of Bell's inequality can only be achieved in the strong-coupling regime.
Fast entangling gates for Rydberg atoms via resonant dipole-dipole interaction
本文提出一种利用每个原子四个能级和微波驱动共振偶极-偶极相互作用的里德伯原子纠缠门方案，实现无需光学相位调制的受控-Z门，比现有范德瓦尔斯门更快且对里德伯衰变更不敏感，并验证了其对距离波动的鲁棒性。
Pulsed lasers offer significant advantages over CW lasers in the coherent control of qubits. Here we review the theoretical and experimental aspects of controlling the internal and external states of individual trapped atoms with pulse trains. Two distinct regimes of laser intensity are identified. When the pulses are sufficiently weak that the Rabi frequency $Ω$ is much smaller than the trap frequency $\otrap$, sideband transitions can be addressed and atom-atom entanglement can be accomplished in much the same way as with CW lasers. By contrast, if the pulses are very strong ($Ω\gg \otrap$),…
We propose a scheme to implement a two-qubit controlled-phase gate for single atomic qubits, which works in principle with nearly ideal success probability and fidelity. Our scheme is based on the cavity input-output process and the single photon polarization measurement. We show that, even with the practical imperfections such as atomic spontaneous emission, weak atom-cavity coupling, violation of the Lamb-Dicke condition, cavity photon loss, and detection inefficiency, the proposed gate is feasible for generation of a cluster state in that it meets the scalability criterion and it operates i…
Entangling free electrons and optical excitations
本文提出通过塑造自由电子波函数轮廓，选择性激发光学腔中的目标模式，从而在自由电子与光学激发之间产生纯纠缠，并以银纳米颗粒等离激元和无机分子振动为例进行理论验证。
The mapping of photonic states to collective excitations of atomic ensembles is a powerful tool which finds a useful application in the realization of quantum memories and quantum repeaters. In this work we show that cold atoms in optical lattices can be used to perform an entangling unitary operation on the transferred atomic excitations. After the release of the quantum atomic state, our protocol results in a deterministic two qubit gate for photons. The proposed scheme is feasible with current experimental techniques and robust against the dominant sources of noise.
Fault-tolerant quantum computation with static atomic buses
研究基于静态原子总线的中性原子架构，通过辅助中介原子实现长程纠缠操作，设计最优控制协议，模拟显示相比原子穿梭架构逻辑错误率大幅改善，为可扩展容错中性原子量子计算提供实用替代方案。
A scheme is presented to perform an entangling gate between two atomic ensembles or Bose-Einstein condensates in a optical cavity with a common optical mode. The method involves using a generalized Stimulated Raman Adiabatic Passage (STIRAP) to adiabatically evolve the ground state. We show that dark states exist for any atom number within the cavities, and find that the operation produces an unusual type of evolution where the minimum of the number of atoms between two levels transitions to another state. This produces a unconventional type of entangling Hamiltonian which creates a phase depe…
Proposed quantum networks require both a quantum interface between light and matter and the coherent control of quantum states. A quantum interface can be realized by entangling the state of a single photon with the state of an atomic or solid-state quantum memory, as demonstrated in recent experiments with trapped ions, neutral atoms, atomic ensembles, and nitrogen-vacancy spins. The entangling interaction couples an initial quantum memory state to two possible light-matter states, and the atomic level structure of the memory determines the available coupling paths. In previous work, these pa…
Individual trapped atomic qubits represent one of the most promising technologies to scale quantum computers, owing to their negligible idle errors and the ability to implement a full set of reconfigurable gate operations via focused optical fields. However, the fidelity of quantum gate operations can be limited by weak confinement of the atoms transverse to the laser. We present measurements of this effect by performing individually-addressed entangling gates in chains of up to 25 trapped atomic ions that are weakly confined along the chain axis. We present a model that accurately describes t…
Cavity polariton blockade for non-local entangling gates with trapped atoms
该研究提出利用腔极化激元阻塞机制，通过公共腔模耦合原子量子比特，实现多量子比特W态及非局域CZ和C2Z门，仅需外部驱动和全局脉冲，无需单比特寻址，并解析了随协同性C缩放的误差。
Cooperative squeezing of internal and collective spins in an atomic ensemble
针对量子计量对超越标准量子极限自旋压缩态的需求，本研究在热铷原子系综中协同结合内自旋与集体自旋两类压缩机制，实现了-6.21±0.84 dB的高性能自旋压缩，为挖掘原子系综量子态自由度潜力提供新路径。
Entangling two giant atoms via a topological waveguide
本文研究两个二能级巨型原子经 SSH 拓扑波导产生纠缠，分析16种耦合构型与主方程动力学，发现五对构型可显著增强纠缠的延迟突然出现。
We analyse a novel squeezing and entangling mechanism which is due to correlated Stokes and anti-Stokes photon forward scattering in a multi-level atom vapour. Following the proposal we present an experimental demonstration of 3.5 dB pulsed frequency nondegenerate squeezed (quadrature entangled) state of light using room temperature caesium vapour. The source is very robust and requires only a few milliwatts of laser power. The squeezed state is generated in the same spatial mode as the local oscillator and in a single temporal mode. The two entangled modes are separated by twice the Zeeman fr…
Entanglement between two macroscopic atomic ensembles induced by measurement on an ancillary light system has proven to be a powerful method for engineering quantum memories and quantum state transfer. Here we investigate the feasibility of such methods for generation, manipulation and detection of genuine multipartite entanglement between mesoscopic atomic ensembles. Our results extend in a non trivial way the EPR entanglement between two macroscopic gas samples reported experimentally in [B. Julsgaard, A. Kozhekin, and E. Polzik, Nature {\bf 413}, 400 (2001)]. We find that under realistic co…
We show the transition from a fully quantized interaction to a semiclassical one in entangled small number quantum systems using the quantum trajectories approach. In particular, we simulate the microwave Ramsey zones used in Rydberg atom interferometry, filling in the gap between the strongly entangling Jaynes Cummings evolution and the semiclassical rotation of the atomic internal states. We also correlate the information flowing with leaking photons to the entanglement generation between cavity field and flying atom and detail the roles played by the strong dissipation and the external driv…
A scheme for entangling distant atoms is realized, as proposed in the seminal paper by Cabrillo et al. [Phys. Rev. A 59, 1025 (1999)]. The protocol is based on quantum interference and detection of a single photon scattered from two effectively one meter distant laser-cooled and trapped atomic ions. The detection of a single photon heralds entanglement of two internal states of the trapped ions with high rate and with a fidelity limited mostly by atomic motion. Control of the entangled state phase is demonstrated by changing the path length of the single-photon interferometer.
Hardware-Efficient Rydberg Atomic Quantum Solvers for NP Problems
本文提出了一种基于Rydberg原子量子计算平台的NP问题求解器，利用可并行化的单量子比特和多量子比特纠缠门，实现线性规模的量子比特需求，具有二次量子加速的高效求解方法。
Entangling microwaves with optical light
本文在毫开尔文环境中利用光脉冲驱动的超导电光器件，首次在超导微波电路与电信波长光之间确定性地制备并验证了纠缠态，突破了巨大能量失配的限制，为混合量子网络发展奠定基础。
High-fidelity parallel entangling gates on a neutral atom quantum computer
本文在中性原子量子计算机上利用最优控制等方法实现了多达60个原子并行、保真度达99.5%的双量子比特纠缠门，超越了表面码纠错阈值，并扩展至低错误的三量子比特门，为大规模量子计算奠定基础。
Detuning-robust Rydberg entangling gates from echoed pulses
本研究设计了抗失谐的里德伯纠缠ZZ门，将一阶失谐误差归为单量子比特Z旋转并由回波序列消除，大幅放宽了对激光频率稳定性等的要求，推动中性原子实用容错量子计算发展。
We sense the motion of a trapped atomic ion using a sequence of state-dependent ultrafast momentum kicks. We use this atom interferometer to characterize a nearly-pure quantum state with $n=1$ phonon and accurately measure thermal states ranging from near the zero-point energy to $\bar{n}\sim 10^4$, with the possibility of extending at least 100 times higher in energy. The complete energy range of this method spans from the ground state to far outside of the Lamb-Dicke regime, where atomic motion is greater than the optical wavelength. Apart from thermometry, these interferometric techniques a…
We describe a novel scheme to implement scalable quantum information processing using Li-Cs molecular state to entangle $^{6}$Li and $^{133}$Cs ultracold atoms held in independent optical lattices. The $^{6}$Li atoms will act as quantum bits to store information, and $^{133}$Cs atoms will serve as messenger bits that aid in quantum gate operations and mediate entanglement between distant qubit atoms. Each atomic species is held in a separate optical lattice and the atoms can be overlapped by translating the lattices with respect to each other. When the messenger and qubit atoms are overlapped,…
This dissertation studies spin squeezing, entanglement and decoherence in large ensembles of cold, trapped alkali atoms with hyperfine spin f interacting with optical fields. Restricting the state of each atom to a qutrit embedded in the 2f+1 dimensional hyperfine spin enables us to efficiently model the coherent and dissipative dynamics of the ensemble. This formalism also allows us to explore the effects of local control on the internal hyperfine spins of the atoms. State preparation using such control increases the entangling power of the atom-light interface for f>1/2. Subsequent control o…
The transfer of entanglement from optical fields to qubits provides a viable approach to entangling remote qubits in a quantum network. In cavity quantum electrodynamics, the scheme relies on the interaction between a photonic resource and two stationary intracavity atomic qubits. However, it might be hard in practice to trap two atoms simultaneously and synchronize their coupling to the cavities. To address this point, we propose and study entanglement transfer from cavities driven by an entangled external field to controlled flying qubits. We consider two exemplary non-Gaussian driving field…
Prospects for reaching persistent entanglement between two spatially separated atomic Bose-Einstein condensates are outlined. The system set-up comprises of two condensates loaded in an optical lattice, which, in return, is confined within a high-Q optical resonator. The system is driven by an external laser that illuminates the atoms such that photons can scatter into the cavity. In the superradiant phase a cavity field is established and we show that the emerging cavity mediated interactions between the two condensates is capable of entangling them despite photon losses. This macroscopic ato…
To advance quantum information science a constant pursuit is the search for physical systems that meet the stringent requirements for creating and preserving quantum entanglement. In atomic physics, robust two-qubit entanglement is typically achieved by strong, long-range interactions in the form of Coulomb interactions between ions or dipolar interactions between Rydberg atoms. While these interactions allow fast gates, atoms subject to these interactions must overcome the associated coupling to the environment and cross-talk among qubits. Local interactions, such as those requiring significa…
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