Single Neutral Atoms Research Articles

Single atoms in the ring lattice for quantum information processing and quantum simulation

We have demonstrated preparing and rotating single neutral rubidium atoms in an optical ring lattice generated by a spatial light modulator, inserting two atoms into a single microscopic optical potential efficiently by dynamically reshaping the optical dipole trap, trapping single atoms in a blue detuned optical bottle beam trap, and confining single atoms into the Lamb-Dicke regime by combining red and blue detuned optical potentials. In combination with the manipulation of internal states of single atoms, the study is opening a way for research in the field of quantum information processing and quantum simulation. In this paper we review the past works and discuss the prospects.

Combining red and blue-detuned optical potentials to form a Lamb-Dicke trap for a single neutral atom

We propose and demonstrate a scheme for strong radial confinement of a single 87 Rb atom by a bichromatic far-off resonance optical dipole trap (BFORT). The BFORT is composed of a blue-detuned Laguerre-Gaussian LG01 beam and a red-detuned Gaussian beam. The atomic oscillation frequency measurement shows that the effective trapping dimension is much sharper than that from a diffraction-limited microscopic objective. Theory shows that the added scattering rate due to imposing blue-detuned light is negligible when the temperature of the single atoms is close to ground state temperature. By carrying out sub-Doppler cooling, the mean energy of single atoms trapped in the BFORT is reduced to 15 ± 1 μK. The corresponding mean quantum number of radial vibration n is about 1.65, which satisfies the Lamb-Dicke regime. We conclude that the BFORT is a suitable Lamb-Dicke trap for further cooling a single neutral atom down to the ground state and for further application in quantum information processing.

Inserting single Cs atoms into an ultracold Rb gas

We report on the controlled insertion of individual Cs atoms into an ultracold Rb gas at about 400 nK. This requires to combine the techniques necessary for cooling, trapping and manipulating single laser cooled atoms around the Doppler temperature with an experiment to produce ultracold degenerate quantum gases. In our approach, both systems are prepared in separated traps and then combined. Our results pave the way for coherent interaction between a quantum gas and a single or few neutral atoms of another species.

Transferring single-atoms between two red-detuned far-off-resonance optical dipole traps

The preparation and manipulation of single neutral atoms in optical dipole traps have important applications in quantum simulation and information. For this purpose, a single neutral atom, trapped in a static optical dipole trap which is formed by a strongly focused red-detuned far-off-resonance laser, can be transferred to a movable optical dipole trap when the movable trap crosses the static trap and the transfer efficiency can reach about 94%, meanwhile this transferred atom could be located at given position in the focal plane. This experimental result has potential applications in realizing entanglement of two individual neutral atoms in an optical dipole trap array.

Entanglement of two ground state neutral atoms using Rydberg blockade

We report on our recent progress in trapping and manipulation of internal states of single neutral rubidium atoms in optical tweezers. We demonstrate the creation of an entangled state between two ground state atoms trapped in separate tweezers using the effect of Rydberg blockade. The quality of the entanglement is measured using global rotations of the internal states of both atoms.

Quantum informatics with single atoms

Current status of the research on the use of single neutral atoms, captured in optical traps, as a quantum computer’s qubits, is briefly reviewed. The specifics of qubits based on cold atoms and t quantum logical operations via dipole interaction by short-time laser excitation in a Rydberg state are discussed. The latest experimental results of the observation of dipole interaction between two Rydberg atoms and of atoms’ entangled states in a ground state are given.

Elimination of the degenerate trajectory of a single atom strongly coupled to a tilted TEM10cavity mode

We demonstrate the trajectory measurement of the single neutral atoms deterministically using a high-finesse optical micro-cavity. Single atom strongly couples to the high-order transverse vacuum TEM_{10} mode, instead of the usual TEM_{00} mode, and the parameter of the system is (g_{10},\kappa ,\gamma )=2\pi \times (20.5,2.6,2.6)MHz. The atoms simply fall down freely from the magneto-optic trap into the cavity modes and the trajectories of the single atoms are linear. The transmission spectrums of atoms passing through the TEM10 mode are detected by a single photon counting modules and well fitted. Thanks to the tilted cavity transverse TEM10 mode, which is inclined to the vertical direction about 45 degrees and it helps us, for the first time, to eliminate the degenerate trajectory of the single atom falling through the cavity and get the unique atom trajectory. Atom position with high precision of 0.1{\mu}m in the off-axis direction (axis y) is obtained, and the spatial resolution of 5.6{\mu}m is achieved in time of 10{\mu}s along the vertical direction (axis x). The average velocity of the atoms is also measured from the atom transits, which determines the temperature of the atoms in magneto-optic trap, 186{\mu}K {\pm} 19{\mu}K.

Feedback control of a single atom in an optical cavity

We discuss feedback control of the motion of a single neutral atom trapped inside a high-finesse optical cavity. Based on the detection of single photons from a probe beam transmitted through the cavity, the position of the atom in the trap is estimated. Following this information, the trapping potential is switched between a high and a low value in order to counteract the atomic motion. This allowed us to increase the storage time by about one order of magnitude. Here, we describe the technical implementation of the feedback loop and give a detailed analysis of its limitations as deduced from Monte-Carlo simulations. We also discuss different strategies to further improve the performance of the feedback.

Coherently walking, rocking and blinding single neutral atoms

Advances in the preparation and detection, but most importantly in the coherent manipulation of single neutral atoms have allowed the observation of intriguing phenomena of quantum physics in recent years. We discuss developments to prepare and detect single neutral atoms in a one-dimensional optical lattice potential with single site resolution. Moreover, using two different experimental techniques, a state-dependent optical lattice potential on the one hand and a high-finesse optical cavity on the other hand, we have obtained coherent control over single neutral atoms. The former has enabled us to observe the quantum walk of atoms in position space, and to coherently control the motion of trapped atoms via microwave radiation. The latter offers a means to non-destructively detect the atomic spin state, thereby revealing quantum jumps of single atoms, or the altered optical properties of single atoms when subject to electromagnetically-induced transparency.

Single Cs atoms as collisional probes in a large Rb magneto-optical trap

We study cold inter-species collisions of Caesium and Rubidium in a strongly imbalanced system with single and few Cs atoms. Observation of the single atom fuorescence dynamics yields insight into light-induced loss mechanisms, while both subsystems can remain in steady-state. This significantly simplifies the analysis of the dynamics, as Cs-Cs collisions are effectively absent and the majority component remains unaffected, allowing us to extract a precise value of the Rb-Cs collision parameter. Extending our results to ground state collisions would allow to use single neutral atoms as coherent probes for larger quantum systems.

Lossless State Detection of Single Neutral Atoms

We introduce lossless state detection of trapped neutral atoms based on cavity-enhanced fluorescence. In an experiment with a single 87Rb atom, a hyperfine-state-detection fidelity of 99.4% is achieved in 85 μs. The quantum bit is interrogated many hundreds of times without loss of the atom while a result is obtained in every readout attempt. The fidelity proves robust against atomic frequency shifts induced by the trapping potential. Our scheme does not require strong coupling between the atom and cavity and can be generalized to other systems with an optically accessible quantum bit.

Continuous Imaging of a Single Neutral Atom in a Variant Magneto-Optical Trap

We demonstrate continuous imaging of a single 87Rb atom confined in a steep magneto-optical trap with an electron-multiplying charge-coupled device (EMCCD) camera and realize a one-dimensional micro-optical trap array with a Dammann grating. We adopt several methods to reduce the noise in the fluorescence signal we obtain with the EMCCD. Step jumping characteristics of the fluorescence demonstrate capturing and losing of individual atoms.

Rotating single atoms in a ring lattice generated by a spatial light modulator

We demonstrated trapping single neutral Rb atoms in micro traps of an optical ring lattice formed by superposing the +/-l components of the Laguerre-Gaussian mode, and generated by reflecting a single laser beam from a computer controlled spatial light modulator. A single atom in one trap or two atoms with one each in two traps were identified by observing the fluorescence. The trap array loaded with single atoms was rotated by dynamically displaying the hologram animation movie on the modulator. The modulation period in the fluorescence indicates the rotation of one or two single atoms in the lattice.

Suppression of phase decoherence in a single atomic qubit

We study the suppression of noise-induced phase decoherence in a single atomic qubit by employing pulse sequences. The atomic qubit is composed of a single neutral atom in a far-detuned optical dipole trap and the phase decoherence may originate from the laser intensity and beam pointing fluctuations, as well as magnetic field fluctuations. We show that suitable pulse sequences may prolong the qubit coherence time substantially as compared with the conventional spin-echo pulse.

Tunneling electroconductance of atomic Bose-Einstein condensates

We consider an electron interacting with a Bose-Einstein condensate of atoms that can form negative ions. The binding energy ${E}_{a}$ of an electron by a single neutral atom gives rise to a continuous band of electronic quantum states resulting from the process of charge exchange among the condensate atoms. When such a condensate is placed in between the two leads done from a material with Fermi energy close to ${E}_{a}$, the lead electrons can tunnel through the condensate via this band thus resulting in the condensate electroconductance. It turns out that this process is very sensitive to the interatomic distance, and it gets strongly suppressed by the quantum fluctuations of the condensate density with respect to the prediction of the mean-field theory as the result. We adapt the standard field theory methods originally developed for description of a particle propagating through a disordered potential and present an exactly soluble analytical model of the process. In contrast with the standard description widely known in the theory of disordered systems, we take into account inelastic processes associated with quantum transitions in the condensate. Possibilities of the experimental observation of the phenomenon are discussed.

微小トロイド共振器を用いたキャビティQED

Cavity quantum electrodynamics (cQED) with systems of single neutral atoms or ions coupled to Fabry-

Fast quantum state control of a single trapped neutral atom

We demonstrate the initialization, readout, and high-speed manipulation of a qubit stored in a single $^{87}\mathrm{Rb}$ atom trapped in a submicrometer-sized optical tweezer. Single-qubit rotations are performed on a time scale below $100\phantom{\rule{0.3em}{0ex}}\mathrm{ns}$ using two-photon Raman transitions. Using the spin-echo technique, we measure an irreversible dephasing time of $34\phantom{\rule{0.3em}{0ex}}\mathrm{ms}$. The readout of the single atom qubit is at the quantum projection noise limit when averaging up to 1000 individual events.

Diffraction-limited optics for single-atom manipulation

We present an optical system designed to capture and observe a single neutral atom in an optical dipole trap, created by focusing a laser beam using a large-numerical-aperture $(\mathrm{NA}=0.5)$ aspheric lens. We experimentally evaluate the performance of the optical system and show that it is diffraction limited over a broad spectral range $(\ensuremath{\sim}200\phantom{\rule{0.3em}{0ex}}\mathrm{nm})$ with a large transverse field $(\ifmmode\pm\else\textpm\fi{}25\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{m})$. The optical tweezer created at the focal point of the lens is able to trap single atoms of $^{87}\mathrm{Rb}$ and to detect them individually with a large collection efficiency. We measure the oscillation frequency of the atom in the dipole trap and use this value as an independent determination of the waist of the optical tweezer. Finally, we produce with the same lens two dipole traps separated by $2.2\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{m}$ and show that the imaging system can resolve the two atoms.

Manipulation of single neutral atoms in optical lattices

We analyze a scheme to manipulate quantum states of neutral atoms at individual sites of optical lattices using focused laser beams. Spatial distributions of focused laser intensities induce position-dependent energy shifts of hyperfine states, which, combined with microwave radiation, allow selective manipulation of quantum states of individual target atoms. We show that various errors in the manipulation process are suppressed below $10^{-4} $ with properly chosen microwave pulse sequences and laser parameters. A similar idea is also applied to measure quantum states of single atoms in optical lattices.

Submicrometer Position Control of Single Trapped Neutral Atoms

We optically detect the positions of single neutral cesium atoms stored in a standing wave dipole trap with a subwavelength resolution of 143 nm rms. The distance between two simultaneously trapped atoms is measured with an even higher precision of 36 nm rms. We resolve the discreteness of the interatomic distances due to the 532 nm spatial period of the standing wave potential and infer the exact number of trapping potential wells separating the atoms. Finally, combining an initial position detection with a controlled transport, we place single atoms at a predetermined position along the trap axis to within 300 nm rms.