Single Atomic State Research Articles

Atomic Structure and Local Electronic States of Single Pt Atoms Dispersed on Graphene

In single-atom catalysis, the atomic structure and local electronic states of single atoms on a supporting material remain a fundamental question. We experimentally and theoretically solved these problems for single Pt atoms dispersed on freestanding graphene using plasma sputtering. Electron microscopy revealed the atomic arrangements of Pt atoms binding to carbon atoms at the step edges of nanographene flakes. X-ray photoelectron spectroscopy revealed a large binding energy shift of the Pt 4f state of a single Pt atom. First-principles calculations elucidated that the Pt 5dxy-orbital in the step edge plays a crucial role in the formation of chemical bonds to C atoms and in the considerable charge transfer from Pt to C atoms, resulting in the large binding energy shift of the Pt 4f state.

Remote state preparation via photonic Faraday rotation in low-Q cavities

Based on the input-output relation in low-Q cavities, we propose a feasible scheme to prepare remotely a single-atom state via photonic Faraday rotation, and then the scheme is generalized to the case of remote preparation of a two-atom entangled state. Our results show that when the coefficients of the initial atomic state to be prepared are real, both remote preparation of the single-atom state and that of the two-atom entangled state can be achieved deterministically by selecting appropriate parameters of the systems for the interactions among the atom, polarized single-photon pulse, and cavity field. Compared with the existing schemes for remote preparation of atomic states, in our scheme photons are used as flying qubits to transmit quantum information, which is suitable indeed to achieve a long-distance atomic state preparation in principle. Due to the fact that the information of atomic state is encoded in two degenerate ground-state levels of a -type three-level atom confined in a unilateral dissipative cavity, and that the atoms are only virtually excited, our schemes are insensitive to both cavity decay and atomic spontaneous emission. Besides, the two schemes we proposed do not need two- or multi-particle orthogonal measurements, only product-state measurements are involved, as well as they work in low-Q regime and do not require a strong coupling condition between the atoms and the optical cavities, which greatly reduce the experimental difficulty.

Quantum State Sharing in the Driven CQED Systems

An experimentally feasible scheme to securely distribute and reconstruct a single-atom quantum state between two parties via a tripartite entangled state in cavity QED has been proposed. If they collaborate, both users can reconstruct and read the distributed secret information.

Probabilistic cloning of a single-atom state via cavity QED

We propose a scheme for probabilistically cloning a two-level state of an atom to a polarization photon via cavity QED system combined with linear optics elements. By choosing appropriate parameters, a controlled phase flip (CPF) gate between the atom and the probe photon is realized. Then we can judge that the cloning process should be continued (with the optimal probability) or interrupted by detecting the probe photon. If the cloning can be continued, the original atom state is deterministically cloned to the cloning photon by performing two more CPF gates and three single-qubit unitary operations. Otherwise, if the detection shows that the cloning should be interrupted, the cloning photon and the relevant operations are omitted.

Entanglement between light and an optical atomic excitation

The generation, distribution and control of entanglement across quantum networks is one of the main goals of quantum information science. In previous studies, hyperfine ground states of single atoms or atomic ensembles have been entangled with spontaneously emitted light. The probabilistic character of the spontaneous emission process leads to long entanglement generation times, limiting realized network implementations to just two nodes. The success probability for atom-photon entanglement protocols can be increased by confining a single atom in a high-finesse optical cavity. Alternatively, quantum networks with superior scaling properties could be achieved using entanglement between light fields and atoms in quantum superpositions of the ground and highly excited (Rydberg) electronic states. Here we report the generation of such entanglement. The dephasing of the optical atomic coherence is inhibited by state-insensitive confinement of both the ground and Rydberg states of an ultracold atomic gas in an optical lattice. Our results pave the way for functional, many-node quantum networks capable of deterministic quantum logic operations between long-lived atomic memories.

Controlled deterministic implantation by nanostencil lithography at the limit of ion-aperture straggling

Solid state electronic devices fabricated in silicon employ many ion implantation steps in their fabrication. In nanoscale devices deterministic implants of dopant atoms with high spatial precision will be needed to overcome problems with statistical variations in device characteristics and to open new functionalities based on controlled quantum states of single atoms. However, to deterministically place a dopant atom with the required precision is a significant technological challenge. Here we address this challenge with a strategy based on stepped nanostencil lithography for the construction of arrays of single implanted atoms. We address the limit on spatial precision imposed by ion straggling in the nanostencil—fabricated with the readily available focused ion beam milling technique followed by Pt deposition. Two nanostencils have been fabricated; a 60 nm wide aperture in a 3 μm thick Si cantilever and a 30 nm wide aperture in a 200 nm thick Si3N4 membrane. The 30 nm wide aperture demonstrates the fabricating process for sub-50 nm apertures while the 60 nm aperture was characterized with 500 keV He+ ion forward scattering to measure the effect of ion straggling in the collimator and deduce a model for its internal structure using the GEANT4 ion transport code. This model is then applied to simulate collimation of a 14 keV P+ ion beam in a 200 nm thick Si3N4 membrane nanostencil suitable for the implantation of donors in silicon. We simulate collimating apertures with widths in the range of 10–50 nm because we expect the onset of J-coupling in a device with 30 nm donor spacing. We find that straggling in the nanostencil produces mis-located implanted ions with a probability between 0.001 and 0.08 depending on the internal collimator profile and the alignment with the beam direction. This result is favourable for the rapid prototyping of a proof-of-principle device containing multiple deterministically implanted dopants.

Quantum State Sharing of an Arbitrary Single-Atom State by Using a Genuine Six-Atom Entangled State in Cavity QED

We demonstrate that a genuine six-atom entangled state can be used to realize the deterministic quantum state sharing of an arbitrary single-atom state in cavity QED. The scheme does not involve Bell-state measurement and is insensitive to both the cavity decay and the thermal field. In our scheme, any one of the two agents is sufficient to reconstruct the original state only under the condition that he/she obtains the help of the other one, but one of them obtains no information.

Undeniable quantum state sharing with a five-atom cluster state in cavity QED

We present an efficient scheme for undeniable five-party quantum state sharing(FQSTS) of an arbitrary single-atom state with a five-atom cluster state in cavity QED. The implementation of this scheme does not involve the joint-state measurement of multi-atoms, which makes it convenient in a practical application. The scheme is also insensitive to the cavity decay and the thermal field.

Teleportation of atomic and photonic states in low-Q cavity QED

We propose two alternative teleportation protocols in low-Q cavity QED. Through the input–output process of photons, we can generate atom-photon entangled states as the quantum channel. Then we propose to teleport single-atom (two-atom entangled) state using coherent photonic states, and to teleport single photonic state with the assistance of three-level atom. The distinct feature of our protocols is that we can teleport both atomic and photonic states via the input–output process of photons in the low-Q cavity. Furthermore, as our protocols work in low-Q cavities and only involve virtual excitation of atoms, they are insensitive to both cavity decay and atomic spontaneous emission, and may be feasible with current technology.

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.

Modification of Magnetic Stability of Co Single Atoms on Pt(111) by Dimer Formation

Novel magnetic properties of very small nanostructures have attracted broad interests in the fields of nanoscience and nanotechnology. The magnetic stability of such nanostructures relies on the magnetic anisotropy and magnetization dynamics. These properties were investigated for single Co atoms on Pt(111) using low-temperature scanning tunneling microscopy. The atomic manipulation capabilities of scanning tunneling microscopy allow to extend the study to Co dimers. Information on the magnetic anisotropy and lifetime of magnetically excited states of single atoms and dimers was achieved simultaneously with inelastic tunneling spectroscopy. Manufactured dimers consist of adatoms in nearest-neighbor fcc-hcp sites. For adatoms this close, a strong direct exchange interaction of 14 meV/h2 was found, much larger than the weak long-range indirect Ruderman-Kittel-Kasuya-Yoshida interaction. [DOI: 10.1380/ejssnt.2011.237]

Frequency stabilization of multiple lasers and Rydberg atom spectroscopy

In this paper we report details of the apparatus and experimental techniques used to excite Rydberg states of 7Li using multiple diode lasers. Special attention is paid to frequency stabilization of the lasers and we show how three lasers can be stabilized using the fluorescence from a single atomic state. Laser spectroscopy of the 8p,9p, and 11p–15p states is then performed to determine the quantum defects of these states. Our measurement precision exceeds that of previous measurements of these defects by as much as a factor of 25. This work substantially extends our previous measurement of the 10p quantum defect, and we compare our measured defects with recent theoretical calculations for the np states across the range 8≤n≤15. The agreement with theory is excellent.

Quantum state engineering by superpositions of coherent states along a straight line with a single atomic state measurement

A new scheme is proposed for preparation of a type of nonclassical state in cavity QED. In the scheme, an atom either flying through or trapped within a cavity, is controlled by the classical Stark effect; this makes it interact alternately with a (resonant) classical field and with the (dispersive) cavity field. The cavity field, which allows an arbitrary displacement operation during the process, after the detection on the atom, finally collapses to the specific superpositions of coherent states, with their weighting factors controllable. The scheme is also applied for preparation of superpositions of motional coherent states for a trapped ion. The scheme is in contrast to all the previous ones, and thus provides a new perspective for quantum state engineering.

Scanning Tunneling Microscopic Investigations into the Conductance of Single-Atom Junctions

Experiments using a scanning tunneling microscope to controllably fabricate single-atom contacts are reviewed. An important feature of this approach is that the electronic and geometric properties of the junctions can be characterized prior to and after contact formation. Investigations on magnetic contacts have led to the observation of unusual conductance values. Spectroscopy of the electronic states of single atoms in contact with the tip is demonstrated through the observation of the Kondo effect and of surface state localization at adsorbed atoms. Time-resolved two-level fluctuations of a single-atom tunneling contact reveal heating of the junction in an otherwise cryogenic environment.

Modified dynamic Stark shift and depopulation rate of an atom inside a Kerr nonlinear blackbody

We investigate the dynamic Stark shift and atomic depopulation rate induced by real photons in a Kerr nonlinear blackbody. We found that the dynamic Stark shift and atomic depopulation rate are equally modified by a nonlinear contribution factor and a linear contribution factor under a transition temperature Tc. The nonlinear contribution factor depends on the Kerr nonlinear coefficient as well as the absolute temperature. Below Tc, the absolute values of the dynamic Stark shift and depopulation rate of a single atomic state (not the ground state) are correspondingly larger than those in a normal blackbody whose interior is filled with a nonabsorbing linear medium. Above Tc, the dynamic Stark shift and atomic depopulation rate are correspondingly equal to those in a normal blackbody with a nonabsorbing linear medium in its interior.

Scheme to Implement Optimal Symmetric 1 → 2 Universal Quantum Telecloning Through Cavity-Assisted Interaction

We propose a scheme to implement the optimal symmetric 1 → 2 universal quantum telecloning through cavity-assisted interaction. In our scheme, an arbitrary single atomic state can be telecloned to two single atomic states. And three atoms are trapped in three spatially separated cavities respectively. With a particular multiparticle entangled state acting as a quantum information channel and the trapped single atom acting as a quantum network node for its long-lived internal state, quantum information can be telecloned among nodes and can stored in the nodes.

An atom and a photon

The coherent control of single-photon emitters as, e.g., single ions or atoms, is a crucial element for mapping quantum information between light and matter. The possibility of generating entanglement between a photon and the emitter system provides an interface between matter-based quantum memories and photonic quantum communication channels, which is the essential resource for quantum repeaters and other future quantum information applications. To generate entangled atom-photon states, in our experiment, we store a single 87Rb atom in an optical dipole trap. The single-atom/single-photon character is confirmed by the observation of photon antibunching in the detected fluorescence light. The spectral properties of single photons emitted by the atom allowed us to determine the mean kinetic energy of the atom corresponding to 105 μK. We describe a single-atom state analysis method which allowed us to characterize the entanglement between the atom and a single photon emitted in the spontaneous decay. We obtain an entanglement fidelity of 89% that clearly shows the high degree of entanglement in our system and potential for further applications in quantum communication.

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.

Observation of Entanglement of a Single Photon with a Trapped Atom

We report the observation of entanglement between a single trapped atom and a single photon at a wavelength suitable for low-loss communication over large distances, thereby achieving a crucial step towards long range quantum networks. To verify the entanglement, we introduce a single atom state analysis. This technique is used for full state tomography of the atom-photon qubit pair. The detection efficiency and the entanglement fidelity are high enough to allow in a next step the generation of entangled atoms at large distances, ready for a final loophole-free Bell experiment.

REMOTE STATE PREPARATION OF QUANTUM STATES VIA CAVITY QED

In this paper, we give an experimentally feasible scheme for the remote state preparation by the prior share of an entangled state in cavity QED. The whole process of the remote state preparation for a single-atom state and a two-atom entangled state is shown. We find that only one classical bit and one single-atom state measurement is needed for the remote state preparation of a multi-atom entangled state.