arXiv subjects

Ron Folman

Publications and source records attributed to Ron Folman.

At least 55 records · Page 3Linked to original sources

arXiv2016

Fifteen Years of Cold Matter on the Atom Chip: Promise, Realizations, and Prospects

Here we review the field of atom chips in the context of Bose-Einstein Condensates (BEC) as well as cold matter in general. Twenty years after the first realization of the BEC and fifteen years after the realization of the atom chip, the latter has been found to enable extraordinary feats: from producing BECs at a rate of several per second, through the realization of matter-wave interferometry, and all the way to novel probing of surfaces and new forces. In addition, technological applications are also being intensively pursued. This review will describe these developments and more, including new ideas which have not yet been realized.

physics.atom-ph↗

arXiv2015

Suppression and enhancement of decoherence in an atomic Josephson junction

We examine the role of interactions for a Bose gas trapped in a double-well potential ("Bose-Josephson junction") when external noise is applied and the system is initially delocalized with equal probability amplitudes in both sites. The noise may have two kinds of effects: loss of atoms from the trap, and random shifts in the relative phase or number difference between the two wells. The effects of phase noise are mitigated by atom-atom interactions and tunneling, such that the dephasing rate may be reduced to half its single-atom value. Decoherence due to number noise (which induces fluctuations in the relative atom number between the wells) is considerably enhanced by the interactions. A similar scenario is predicted for the case of atom loss, even if the loss rates from the two sites are equal. In fact, interactions convert the increased uncertainty in atom number (difference) into (relative) phase diffusion and reduce the coherence across the junction. We examine the parameters relevant for these effects using a simple model of the trapping potential based on an atom chip device. These results provide a framework for mapping the dynamical range of barriers engineered for specific applications and sets the stage for more complex circuits ("atomtronics").

quant-ph↗

arXiv2015

A self-interfering clock as a "which path" witness

We experimentally demonstrate a new interferometry paradigm: a self-interfering clock. We split a clock into two spatially separated wave packets, and observe an interference pattern with a stable phase showing that the splitting was coherent, i.e., the clock was in two places simultaneously. We then make the clock wave packets "tick" at different rates to simulate a proper time lag. The entanglement between the clock's time and its path yields "which path" information, which affects the visibility of the clock's self-interference. By contrast, in standard interferometry, time cannot yield "which path" information. As a clock we use an atom prepared in a superposition of two spin states. This first proof-of-principle experiment may have far-reaching implications for the study of time and general relativity and their impact on fundamental quantum effects such as decoherence and wave packet collapse.

quant-ph↗

arXiv2015

Long spatial coherence times a few micro-meters from a room temperature surface

The search for quantum coherence based on isolated atoms integrated with a room temperature solid state device (so-called atomchip [1-3]) has been intensifying in the last decade, with advances being made towards applications such as clocks, quantum information processing, surface probing and acceleration and gravitational field sensors. Such a device will also enable (and to some extent has already enabled) novel experiments in fundamental physics (e.g., [4-7]). Here we report on the trapping and maintenance of spatial coherence of atoms (in a Bose-Einstein Condensate -- BEC) about 5$μ$m from a room temperature surface, reducing significantly the distance previously achieved between the spatially coherent atoms and their classical environment [8-12], and most importantly entering the regime where atomic circuits are enabled. In addition, we enter the interesting regime in which the distance to the surface is much smaller than the probed coherence length, a regime in which the spatial dephasing reaches its maximal rate.

quant-ph↗

arXiv2014

Phase space tomography of cold-atoms dynamics in a weakly corrugated potential

We demonstrate tomographic reconstruction of the phase space distribution of atoms oscillating in a harmonic trap with weak potential corrugation caused by nanoscale imperfections in an atom chip. We find that deformations in these distributions are highly sensitive to anharmonic components of the potential. They are explained in terms of angular velocity dispersion of isoenergetic phase space trajectories. We show that the method is applicable for probing classical and quantum dynamics of cold atoms, and we note its importance for future technological applications.

quant-ph↗

arXiv2013

Magic frequencies in atom-light interaction for precision probing of the density matrix

We analyze theoretically and experimentally the existence of a {\it magic frequency} for which the absorption of a linearly polarized light beam by vapor alkali atoms is independent of the population distribution among the Zeeman sub-levels and the angle between the beam and a magnetic field. The phenomenon originates from a peculiar cancelation of the contributions of higher moments of the atomic density matrix, and is described using the Wigner-Eckart theorem and inherent properties of Clebsch-Gordan coefficients. One important application is the robust measurement of the hyperfine population.

quant-ph↗

arXiv2013

Damping of local Rabi oscillations in the presence of thermal motion

We investigate both theoretically and experimentally the effect of thermal motion of laser cooled atoms on the coherence of Rabi oscillations induced by an inhomogeneous driving field. The experimental results are in excellent agreement with the derived analytical expressions. For freely falling atoms with negligible collisions, as those used in our experiment, we find that the amplitude of the Rabi oscillations decays with time $t$ as $\exp[-(t/τ)^4]$, where the coherence time $τ$ drops with increasing temperature and field gradient. We discuss the consequences of these results regarding the fidelity of Rabi rotations of atomic qubits. We also show that the process is equivalent to the loss of coherence of atoms undergoing a Ramsey sequence in the presence of static magnetic field gradients - a common situation in many applications. In addition, our results are relevant for determining the resolution when utilizing atoms as field probes. Using numerical calculations, our model can be easily extended to situations in which the atoms are confined by a potential or to situations where collisions are important.

quant-ph↗

arXiv2012

Two-particle quantum transmission

Two-photon interference is a fundamental phenomenon in quantum mechanics and stands at the base of numerous experimental observations. Here another manifestation of this phenomenon is described, taking place at a Y junction. Specifically it is shown how the r^2+t^2 term which is behind previous observations of two-photon interference, may give rise to different states at a beam-splitter and different two-particle transmission coefficients at a Y junction. Different from previous descriptions of quantum transmission based on one-particle physics, the enhanced transmission described here is due to two-particle physics.

quant-ph↗

arXiv2012

High momentum splitting of matter-waves by an atom chip field gradient beam-splitter

The splitting of matter-waves into a superposition of spatially separated states is a fundamental tool for studying the basic tenets of quantum mechanics and other theories, as well as a building block for numerous technological applications. We report the realization of a matter-wave beam splitter based on magnetic field gradients on an atom chip, which can be used for freely propagating or trapped atoms in a Bose-Einstein condensate or a thermal state. It has a wide dynamic range of momentum transfer and operation time. Differential velocities exceeding 0.5 m/s can be achieved in a few micro-seconds. The beam splitter may enable a wide range of applications, such as, fundamental studies of many-body entanglement and dephasing processes, probing classical and quantum properties of nearby solids, and metrology of rotation, acceleration and gravity on a chip scale.

physics.atom-ph↗

arXiv2012

On the possibility of a relativistic correction to the E and B fields around a current-carrying wire

It is well known that electric and magnetic fields may change when they are observed from different frames of reference. For example, the motion of a charged probe particle moving parallel to a current-carrying wire would be described by utilizing different electric or magnetic fields, depending on from which frame of reference the system is observed and described. To describe the situation in all frames by utilizing the theory of relativity, one has to first describe the situation in one particular frame, and this choice in the case of a current-carrying wire is the topic of this paper. In this study I examine an alternative to the standard choice, and consider its theoretical and experimental validity. An outcome of the alternative approach is that in the rest frame of a wire, running a current introduces also an electric field by giving rise to a minute charge. Present day experimental sensitivities, specifically those of cold ions, may be able to differentiate between the observable signatures predicted by the different approaches.

physics.class-ph↗

arXiv2011

Material Science for Quantum Computing with Atom Chips

In its most general form, the atom chip is a device in which neutral or charged particles are positioned in an isolating environment such as vacuum (or even a carbon solid state lattice) near the chip surface. The chip may then be used to interact in a highly controlled manner with the quantum state. I outline the importance of material science to quantum computing (QC) with atom chips, where the latter may be utilized for many, if not all, suggested implementations of QC. Material science is important both for enhancing the control coupling to the quantum system for preparation and manipulation as well as measurement, and for suppressing the uncontrolled coupling giving rise to low fidelity through static and dynamic effects such as potential corrugations and noise. As a case study, atom chips for neutral ground state atoms are analyzed and it is shown that nanofabricated wires will allow for more than $10^4$ gate operations when considering spin-flips and decoherence. The effects of fabrication imperfections and the Casimir-Polder force are also analyzed. In addition, alternative approaches to current-carrying wires are briefly described. Finally, an outlook of what materials and geometries may be required is presented, as well as an outline of directions for further study.

quant-ph↗

arXiv2008

Superconducting atom chips: advantages and challenges

Superconductors are considered in view of applications to atom chip devices. The main features of magnetic traps based on superconducting wires in the Meissner and mixed states are discussed. The former state may mainly be interesting for improved atom optics, while in the latter, cold atoms may provide a probe of superconductor phenomena. The properties of a magnetic side guide based on a single superconducting strip wire placed in an external magnetic field are calculated analytically and numerically. In the mixed state of type II superconductors, inhomogeneous trapped magnetic flux, relaxation processes and noise caused by vortex motion are posing specific challenges for atom trapping.

quant-ph↗

arXiv2006

Simultaneous optical trapping and detection of atoms by microdisk resonators

We propose a scheme for simultaneously trapping and detecting single atoms near the surface of a substrate using whispering gallery modes of a microdisk resonator. For efficient atom-mode coupling the atom should be placed within approximately 150 nm from the disk. We show that a combination of red and blue detuned modes can form an optical trap at such distances while the back-action of the atom on the field modes can simultaneously be used for atom detection. We investigate these trapping potentials including van-der-Waals and Casimir-Polder forces and discuss corresponding atom detection efficiencies, depending on a variety of system parameters. Finally, we analyze the feasibility of non-destructive detection.

quant-ph↗

arXiv2006

One-mirror Fabry-Perot and one-slit Young interferometry

We describe a new and distinctive interferometry in which a probe particle scatters off a superposition of locations of a single free target particle. In one dimension, probe particles incident on superposed locations of a single "mirror" can interfere as if in a Fabry-Perot interferometer; in two dimensions, probe particles scattering off superposed locations of a single "slit" can interfere as if in a two-slit Young interferometer. The condition for interference is loss of orthogonality of the target states and reduces, in simple examples, to transfer of orthogonality from target to probe states. We analyze experimental parameters and conditions necessary for interference to be observed.

quant-ph↗

arXiv2004

Single-atom detection using whispering gallery modes of microdisk resonators

We investigate the possibility of using dielectric microdisk resonators for the optical detection of single atoms trapped and cooled in magnetic microtraps near the surface of a substrate. The bound and evanescent fields of optical whispering gallery modes are calculated and the coupling to straight waveguides is investigated using finite-difference time domain solutions of Maxwell's equations. Results are compared with semi-analytical solutions based on coupled mode theory. We discuss atom detection efficiencies and the feasibility of non-destructive measurements in such a system depending on key parameters such as disk size, disk-waveguide coupling, and scattering losses.

quant-ph↗

arXiv2002

Fundamental Limits for Coherent Manipulation on Atom Chips

The limitations for the coherent manipulation of neutral atoms with fabricated solid state devices, so-called `atom chips', are addressed. Specifically, we examine the dominant decoherence mechanism, which is due to the magnetic noise originating from the surface of the atom chip. It is shown that the contribution of fluctuations in the chip wires at the shot noise level is not negligible. We estimate the coherence times and discuss ways to increase them. Our main conclusion is that future advances should allow for coherence times as long as one second, a few micrometers away from the surface.

quant-ph↗

arXiv2002

Towards single-atom detection on a chip

We investigate the optical detection of single atoms held in a microscopic atom trap close to a surface. Laser light is guided by optical fibers or optical micro-structures via the atom to a photo-detector. Our results suggest that with present-day technology, micro-cavities can be built around the atom with sufficiently high finesse to permit unambiguous detection of a single atom in the trap with 10 $μ$s of integration. We compare resonant and non-resonant detection schemes and we discuss the requirements for detecting an atom without causing it to undergo spontaneous emission.

quant-ph↗

arXiv2002

Multi Mode Interferometer for Guided Matter Waves

We describe the fundamental features of an interferometer for guided matter waves based on Y-beam splitters and show that, in a quasi two-dimensional regime, such a device exhibits high contrast fringes even in a multi mode regime and fed from a thermal source.

quant-ph↗