Levitated optomechanics:From single to many-body physics

The levitated optomechanics,because of its ultra-high mechanical Q>1010,is considered to be one of the best testbeds for macroscopic quantum superpostions.In this perspective,we give a brief review on the development of the levitated optomechanics,focusing on the macroscopic quantum phenomena,and the applications in quantum precision measurement.The levitated nanodiamond with built-in nitrogen-vacancy centers is discussed as an example.Finally,we discuss the future dirctions of the levtated optomechanics,such as the space-based experiments,the arrays of levitated optomechanics and applications in quantum simulation.

Quantum superposition, entanglement, and state teleportation of a microorganism on an electromechanical oscillator

Schrdinger's thought experiment to prepare a cat in a superposition of both alive and dead states reveals profound consequences of quantum mechanics and has attracted enormous interests. Here we propose a straightforward method to create quantum superposition states of a living microorganism by putting a small cryopreserved bacterium on top of an electromechanical oscillator. Our proposal is based on recent developments that the centerof-mass oscillation of a 15-lm-diameter aluminum membrane has been cooled to its quantum ground state(Teufel et al. in Nature 475:359, 2011), and entangled with a microwave field(Palomaki et al. in Science 342:710,2013). A microorganism with a mass much smaller than the mass of the electromechanical membrane will not significantly affect the quality factor of the membrane and can be cooled to the quantum ground state together with themembrane. Quantum superposition and teleportation of its center-of-mass motion state can be realized with the help of superconducting microwave circuits. More importantly, the internal states of a microorganism, such as the electron spin of a glycine radical, can be entangled with its center-ofmass motion and teleported to a remote microorganism.Our proposal can be realized with state-of-the-art technologies. The proposed setup is a quantum-limited magnetic resonance force microscope. Since internal states of an organism contain information, our proposal also provides a scheme for teleporting information or memories between two remote organisms.

Single photon sources with single semiconductor quantum dots

In t.his contribution, we briefly recall the basic concepts of quantum optics and properties of semicon- ductor quantum clot. （QD） which a.re necessary to the nnderstanding of the physics of single-photon generation with single QDs. Firstly, we address the theory of quantmn emitter-cavity system, the fluorescence and optical properties of semiconductor QDs, and the photon statistics as well as opti- cal properties of the QDs. We then review the localizatioll of single semiconductor QDs in quantum confined optical microcavity systems to achieve their overall optical properties and perfornances in terms of strong coupling regime, elfieiency, directionality, and polarization control. Furthermore, we will discuss the recenl, progress on the fabrication of single photon sources, and various a.pproaehes for embedding single QDs into mieroca,vities or photonic crystal nanoeavities and show how to ex- tend the wavelength range. We focus in part;icular on new generations of electrically driven QD single photon source leading to high repetition rates, efficiencies at elevated temperature operation. Besides strong eoupling regime, and high collection new development;s of room temperature sin- gle photon emission in the strong coupling regime are reviewed. The generation of indistinguishable photons and remaining challenges for pract ical single-photon sources are also discussed.

Nonadiabatic dynamics and geometric phase of an ultrafast rotating electron spin

The spin in a rotating frame has attracted a lot of attentions recently,as it deeply relates to both fundamental physics such as pseudo-magnetic field and geometric phase,and applications such as gyroscopic sensors.However,previous studies only focused on adiabatic limit,where the rotating frequency is much smaller than the spin frequency.Here we propose to use a levitated nano-diamond with a built-in nitrogen-vacancy(NV)center to study the dynamics and the geometric phase of a rotating electron spin without adiabatic approximation.We find that the transition between the spin levels appears when the rotating frequency is comparable to the spin frequency at zero magnetic field.Then we use Floquet theory to numerically solve the spin energy spectrum,study the spin dynamics and calculate the geometric phase under a finite magnetic field,where the rotating frequency to induce resonant transition could be greatly reduced.

Greenberger-Horne-Zeilinger test for multi-dimension and arbitrary time nodes entangled histories

Quantum entanglement,since proposed by Einstein,Podolsky and Rosen(EPR)[1]and further explored by Schr?dinger[2]in1935,has always been the focus of quantum physics realm.The EPR paradox revealed the conflict between quantum theory and local realism.Almost 30 years later,in 1964,Bell first came up with the prototype of a family of inequalities,which was later called Bell inequality[3,4],to express certain limitation that every local clas-

量子纠错码的多平台验证

作为下一代信息技术,量子计算利用量子叠加和量子纠缠实现计算的加速.由于量子态十分脆弱,极易被环境带来的噪声所影响,为了确保计算的可靠性,需要额外的技术来保护量子态不受噪声的影响,这种技术被称为量子纠错.由于实现量子纠错通常对量子系统的规模和量子操作的保真度有着较高要求,因此难以在实验中展示量子纠错带来的提升.本文提出了一种针对探测振幅衰减信道的两量子比特纠错码,并在光学平台、IBM量子云、以及核磁共振量子计算机上实现了该纠错码.实验结果显示,对于以上各个系统,在超过一定错误率阈值后,量子纠错带来的优势将会得以展现.在此基础上,文章对比了实验中使用各个量子系统的特性,并分析了含噪声中等规模量子计算系统(NISQ)实现量子纠错的主要障碍,展示了在当前量子平台上实现量子纠错所带来的优势.

Detection of Magnetic Field Gradient and Single Spin Using Optically Levitated Nano-Particle in Vacuum

Optically levitated nano-particle with spins is a promising system for high-precision measurement and quantum information processing. We theoretically analyze the ratio between the fluctuation of particle's displacement caused by spins in magnetic field and caused by molecular collisions of the residual air. When the ratio is larger than unity, the displacement fluctuation of spins flipping can be remarkably detected. By theoretical analysis and numerical simulation, we propose and validate a scheme for the detection of gradient of the magnetic field by levitating ferromagnetic nano-particle, and also put forward a realizable detection scheme of the single spin by levitating nano-diamond particle with single nitrogen-vacancy(NV) centers.

External control of qubit-photon interaction and multi-qubit reset in a dissipative quantum network

A quantum network is a promising quantum many-body system because of its tailored geometry and controllable interaction. Here,we propose an external control scheme for the qubit-photon interaction and multiqubit reset in a dissipative quantum network,which comprises superconducting circuit chains with microwave drives and filter-filter couplings. The traditional multiqubit reset of the quantum network requires physically disconnected qubits to prevent their entanglement. However, we use an original effect of dissipation, i.e., consuming the entanglement generated by qubits’ interaction, to achieve an external control of the multiqubit reset in an always-connected superconducting circuit. The reset time is independent of the number of qubits in the quantum network. Our proposal can tolerate considerable fluctuations in the system parameters and can be applicable to higherdimensional quantum networks.

Efficiently simulating the work distribution of multiple identical bosons with boson sampling

Boson sampling has been theoretically proposed and experimentally demonstrated to show quantum computational advantages.However,it still lacks the deep understanding of the practical applications of boson sampling.Here we propose that boson sampling can be used to efficiently simulate the work distribution of multiple identical bosons.We link the work distribution to boson sampling and numerically calculate the transition amplitude matrix between the single-boson eigenstates in a one-dimensional quantum piston system,and then map the matrix to a linear optical network of boson sampling.The work distribution can be efficiently simulated by the output probabilities of boson sampling using the method of the grouped probability estimation.The scheme requires at most a polynomial number of the samples and the optical elements.Our work opens up a new path towards the calculation of complex quantum work distribution using only photons and linear optics.