Quantum States Of Atoms Research Articles

Scalable architecture for quantum information processing with atoms in optical micro-structures

We review recent experimental progress towards quantum information processing and quantum simulation using neutral atoms in two-dimensional (2D) arrays of optical microtraps as 2D registers of qubits. We describe a scalable quantum information architecture based on micro-fabricated optical elements, simultaneously targeting the important issues of single-site addressability and scalability. This approach provides flexible and integrable configurations for quantum state storage, manipulation, and retrieval. We present recent experimental results on the initialization and coherent one-qubit rotation of up to 100 individually addressable qubits, the coherent transport of atomic quantum states in a scalable quantum shift register, and discuss the feasibility of two-qubit gates in 2D microtrap arrays.

Cold Atoms Reveal Their Crystalline Nature

Experimentalists have mapped the quantum states (band structure) of cold atoms mimicking electrons in a crystal. The technique should allow researchers to study new aspects of electrons in crystals using the atoms as a model.

Adiabatic Mode Conversion in Multimode Waveguides Using Chirped Computer-Generated Planar Holograms

We discuss the design of a mode converter based on optical analogy of adiabatic passage via a level crossing in multimode waveguides. Computer-generated planar holograms are used to implement the chirped gratings that mimic the laser excitation used in the transfer between quantum states of atoms and molecules. The mode coupling properties are analyzed using the coupled mode theory and shown to resemble the level crossing process. Key features of the devices are illustrated with theoretical calculations and numerical examples. The proposed mode converter shows a bandwidth in excess of 300 nm in the optical communications band.

Time- and frequency-resolved detection of atomic coherence in the regime of strong-field interaction with intense femtosecond laser pulses

Understanding the effect of strong laser pulses on the evolution of an atomic or molecular wave function is important in the context of coherent control in the strong-field regime, when power broadening and dynamic Stark shifts become comparable with or bigger than the bandwidth of the control field. We experimentally demonstrate the method of complete characterization of a complex-valued amplitude of a quantum state driven by a strong two-photon field. The method is based on coherent scattering of a weak probe pulse from the strong-field-induced atomic coherence, followed by the detection of the time- and frequency-resolved parametric four-wave-mixing signal. We show that the proposed technique corresponds to a cross-correlation frequency-resolved optical gating (XFROG) of the highly perturbed evolution of an atomic quantum state. Utilizing the XFROG retrieval algorithm, we determine both the amplitude and phase of an atomic wave function at any time moment throughout the interaction with the driving field. The direct retrieval of the time-dependent phase of the wave function, rather than the population dynamics only, enables us to observe the strong-field effects with arbitrary time and frequency resolution.

Mode Conversion/Splitting by Optical Analogy of Multistate Stimulated Raman Adiabatic Passage in Multimode Waveguides

We propose and describe mode converter/splitter based on optical analogy of multistate stimulated Raman adiabatic passage in multimode waveguides. Computer-generated planar holograms are used to implement the coupling coefficients that mimic the optical pulses used in the transfer among quantum states of atoms and molecules. The mode coupling properties in multimode waveguides are analyzed using the coupled-mode theory and shown to resemble the multistate stimulated Raman adiabatic passage process. Key features of multistate systems are illustrated with theoretical calculations and numerical examples. Mode converter and splitter are designed based on the theoretical analysis and verified using beam propagation simulations.

Coherent Transport of Atomic Quantum States in a Scalable Shift Register

We demonstrate the coherent transport of 2D arrays of small ensembles of neutral atoms in a shift register architecture based on 2D arrays of microlenses. We show the scalability of the transport process by presenting the repeated hand over of atoms from site to site. We prove the conservation of coherence during transport, reloading, and a full shift register cycle. This shows that the fundamental shift sequence can be cascaded and thus scaled to complex and versatile 2D architectures for atom-based quantum information processing, quantum simulation, and the investigation of quantum degenerate gases.

Slow light on a chip via atomic quantum state control

Researchers exploit atomic quantum state control in a fully integrated photonic atomic spectroscopy chip to reduce the group velocity of light by a factor of 1,200 — the lowest group velocity ever reported for a solid-state material. The findings will enable the creation of on-chip nonlinear optical devices with enhanced quantum coherence operating at ultralow power levels.

Detecting quantum coherence of Bose gases in optical lattices by scattering light intensity in cavity

We propose a new method of detecting quantum coherence of a Bose gas trapped in a one-dimensional optical lattice by measuring the light intensity from Raman scattering in cavity. After pump and displacement process, the intensity or amplitude of scattering light is different for different quantum states of a Bose gas, such as superfluid and Mott-Insulator states. This method can also be useful to detect quantum states of atoms with two components in an optical lattice.

A trapped single ion inside a Bose–Einstein condensate

Improved control of the motional and internal quantum states of ultracold neutral atoms and ions has opened intriguing possibilities for quantum simulation and quantum computation. Many-body effects have been explored with hundreds of thousands of quantum-degenerate neutral atoms, and coherent light-matter interfaces have been built. Systems of single or a few trapped ions have been used to demonstrate universal quantum computing algorithms and to search for variations of fundamental constants in precision atomic clocks. Until now, atomic quantum gases and single trapped ions have been treated separately in experiments. Here we investigate whether they can be advantageously combined into one hybrid system, by exploring the immersion of a single trapped ion into a Bose-Einstein condensate of neutral atoms. We demonstrate independent control over the two components of the hybrid system, study the fundamental interaction processes and observe sympathetic cooling of the single ion by the condensate. Our experiment calls for further research into the possibility of using this technique for the continuous cooling of quantum computers. We also anticipate that it will lead to explorations of entanglement in hybrid quantum systems and to fundamental studies of the decoherence of a single, locally controlled impurity particle coupled to a quantum environment.

Cavity quantum optomechanics of ultracold atoms in an optical lattice: Normal-mode splitting

We consider the dynamics of a movable mirror (cantilever) of a cavity coupled through radiation pressure to the light scattered from ultracold atoms in an optical lattice. Scattering from different atomic quantum states creates different quantum states of the scattered light, which can be distinguished by measurements of the displacement spectrum of the cantilever. We show that for large pump intensities the steady state displacement of the cantilever shows bistable behaviour. Due to atomic back-action, the displacement spectrum of the cantilever is modified and depends on the position of the condensate in the Brillouin zone. We further analyze the occurrence of splitting of the normal mode into three modes due to mixing of the mechanical motion with the fluctuations of the cavity field and the fluctuations of the condensate with finite atomic two-body interaction. The present system offers a novel scheme to coherently control ultracold atoms as well as cantilever dynamics.

QUANTUM NANOTECHNOLOGY

Nanotechnology is based on manipulations of individual atoms and molecules to build complex atomic structures. Quantum nanotechnology is a broad concept that deals with a manipulation of individual quantum states of atoms and molecules. Quantum nanotechnology differs from nanotechnology as a quantum computer differs from a classical molecular computer. The nanotechnology deals with a manipulation of quantum states in bulk rather than individually. In this paper, we define the main notions of quantum nanotechnology. Quantum analogs of assemblers, replicators and self-reproducing machines are discussed. We prove the possibility of realizing these analogs. A self-cloning (self-reproducing) quantum machine is a quantum machine which can make a copy of itself. The impossibility of ideally cloning an unknown quantum state is one of the basic rules of quantum theory. We prove that quantum machines cannot be self-cloning if they are Hamiltonian. There exist quantum non-Hamiltonian machines that are self-cloning machines. Quantum nanotechnology allows us to build quantum nanomachines. These nanomachines are not only small machines of nanosize. Quantum nanomachines should use new (quantum) principles of work.

Single atom doping for quantum device development in diamond and silicon

The ability to inject dopant atoms with high spatial resolution, flexibility in dopant species, and high single ion detection fidelity opens opportunities for the study of dopant fluctuation effects and the development of devices in which function is based on the manipulation of quantum states in single atoms, such as proposed quantum computers. The authors describe a single atom injector, in which the imaging and alignment capabilities of a scanning force microscope (SFM) are integrated with ion beams from a series of ion sources and with sensitive detection of current transients induced by incident ions. Ion beams are collimated by a small hole in the SFM tip and current changes induced by single ion impacts in transistor channels enable reliable detection of single ion hits. They discuss resolution limiting factors in ion placement and processing and paths to single atom (and color center) array formation for systematic testing of quantum computer architectures in silicon and diamond.

Optimal control of atom transport for quantum gates in optical lattices

By means of optimal control techniques we model and optimize the manipulation of the external quantum state (center-of-mass motion) of atoms trapped in adjustable optical potentials. We consider in detail the cases of both noninteracting and interacting atoms moving between neighboring sites in a lattice of a double-well optical potentials. Such a lattice can perform interaction-mediated entanglement of atom pairs and can realize two-qubit quantum gates. The optimized control sequences for the optical potential allow transport faster and with significantly larger fidelity than is possible with processes based on adiabatic transport.

Ultrafast strong-field dissociative ionization dynamics of CH2Br2 probed by femtosecond soft x-ray transient absorption spectroscopy

Femtosecond time-resolved soft x-ray transient absorption spectroscopy based on a high-order harmonic generation source is used to investigate the dissociative ionization of CH(2)Br(2) induced by 800 nm strong-field irradiation. At moderate laser peak intensities (2.0 x 10(14) Wcm(2)), strong-field ionization is accompanied by ultrafast C-Br bond dissociation, producing both neutral Br ((2)P(32)) and Br(*) ((2)P(12)) atoms together with the CH(2)Br(+) fragment ion. The measured rise times for Br and Br(*) are 130+/-22 fs and 74+/-10 fs, respectively. The atomic bromine quantum state distribution shows that the BrBr(*) population ratio is 8.1+/-3.8 and that the Br (2)P(32) state is not aligned. The observed product distribution and the time scales of the photofragment appearances suggest that multiple field-dressed potential energy surfaces are involved in the dissociative ionization process. At higher laser peak intensities (6.2 x 10(14) Wcm(2)), CH(2)Br(2) (+) undergoes sequential ionization to form the metastable CH(2)Br(2) (2+) dication. These results demonstrate the potential of core-level probing with high-order harmonic transient absorption spectroscopy for studying ultrafast molecular dynamics.

Quantum Computing with Collective Ensembles of Multilevel Systems

We propose a new physical approach for encoding and processing of quantum information in ensembles of multilevel quantum systems, where the different bits are not carried by individual particles but associated with the collective population of different internal levels. One- and two-bit gates are implemented by collective internal state transitions taking place in the presence of an excitation blockade mechanism, which restricts the population of each internal state to the values zero and unity. Quantum computers with 10-20 bits can be built via this scheme in single trapped clouds of ground state atoms subject to the Rydberg excitation blockade mechanism, and the linear dependence between register size and the number of internal quantum states in atoms offers realistic means to reach larger registers.

Light scattering from ultracold atoms in optical lattices as an optical probe of quantum statistics

We study off-resonant collective light scattering from ultracold atoms trapped in an optical lattice. Scattering from different atomic quantum states creates different quantum states of the scattered light, which can be distinguished by measurements of the spatial intensity distribution, quadrature variances, photon statistics, or spectral measurements. In particular, angle-resolved intensity measurements reflect global statistics of atoms (total number of radiating atoms) as well as local statistical quantities (single-site statistics even without optical access to a single site) and pair correlations between different sites. As a striking example we consider scattering from transversally illuminated atoms into an optical cavity mode. For the Mott-insulator state, similar to classical diffraction, the number of photons scattered into a cavity is zero due to destructive interference, while for the superfluid state it is nonzero and proportional to the number of atoms. Moreover, we demonstrate that light scattering into a standing-wave cavity has a nontrivial angle dependence, including the appearance of narrow features at angles, where classical diffraction predicts zero. The measurement procedure corresponds to the quantum nondemolition measurement of various atomic variables by observing light.

Evaluation of the geometric phase of a two-level atom manipulated on the Bloch sphere using a time-domain atom interferometer

The geometric manipulation of the quantum states of two-level atoms with two laser-controlled resonant {pi} pulses with a relative phase difference was evaluated using a time-domain atom interferometer comprising a cold sodium atom ensemble and two copropagating two-photon Raman pulses. It was verified that the relative phase shift between two states is double the control phase difference and that the rotation around the axis 3 of the Bloch sphere can be controlled by geometric manipulation.

Cavity-Enhanced Light Scattering in Optical Lattices to Probe Atomic Quantum Statistics

Different quantum states of atoms in optical lattices can be nondestructively monitored by off-resonant collective light scattering into a cavity. Angle resolved measurements of photon number and variance give information about atom-number fluctuations and pair correlations without single-site access. Observation at angles of diffraction minima provides information on quantum fluctuations insensitive to classical noise. For transverse probing, no photon is scattered into a cavity from a Mott insulator phase, while the photon number is proportional to the atom number for a superfluid.

Micro traps for quantum information processing and precision force sensing

AbstractWe review recent experimental progress towards quantum information processing and precision force sensing using neutral atoms in micro traps. Microscopic potential structures as generated by optical or electronic microstructures (micro traps) allow for a versatile manipulation of quantum states of atoms and of ultracold atomic quantum gases. Most recent experimental results include the implementation of single‐qubit‐operations in both, optical and magnetic micro traps, as well as in the demonstration of matter‐wave interferometer using Bose‐Einstein condensates coherently split in micro traps.

Entropy squeezing of a moving atom and control of noise of the quantum mechanical channel via the two-photon process

Based on the quantum information theory, we have investigated the entropy squeezing of a moving two-level atom interacting with the coherent field via the quantum mechanical channel of the two-photon process. The results are compared with those of atomic squeezing based on the Heisenberg uncertainty relation. The influences of the atomic motion and field-mode structure parameter on the atomic entropy squeezing and on the control of noise of the quantum mechanical channel via the two-photon process are examined. Our results show that the squeezed period, duration of optimal entropy squeezing of a two-level atom and the noise of the quantum mechanical channel can be controlled by appropriately choosing the atomic motion and the field-mode structure parameter, respectively. The quantum mechanical channel of two-photon process is an ideal channel for quantum information (atomic quantum state) transmission. Quantum information entropy is a remarkably accurate measure of the atomic squeezing.