Atom interferometer based on Bragg scattering from standing light waves

Effect of atom diffusion on the efficiency of Bragg diffraction in atom interferometers

The transition efficiency of atomic Bragg diffraction as mirrors and beam splitters in Bragg atom interferometers plays an essential role in impacting the fringe contrast and measurement sensitivity. This can be attributed to the properties of atomic sources, Bragg pulse shapes, the pulse duration, and the relative position deviation of the atoms and Bragg pulses. Here, we investigate the effect of the atomic source's diffusion and velocity width on the efficiency of Bragg diffraction of the moving cold atomic cloud. The transfer efficiency of Bragg mirrors and beam splitters are numerically simulated and experimentally measured, which are well consistent in comparison. We quantify these effects of atomic diffusion and velocity width and precisely compute how Bragg pulses' efficiencies vary as functions of these parameters. Our results and methodology allow us to optimize the Bragg pulses at different atomic sources and will help in the design of large momentum transfer mirrors and beam splitters in atom interferometry experiments.

Robust Optimized Pulse Schemes for Atomic Fountain Interferometry

The robustness of an atomic fountain interferometer with respect to variations in the initial velocity of the atoms and deviations from the optimal pulse amplitude is examined. We numerically simulate the dynamics of an interferometer in momentum space with a maximum separation of 20ℏk and map out the expected signal contrast depending on the variance of the initial velocity distribution and the value of the laser field amplitude. We show that an excitation scheme based on rapid adiabatic passage significantly enhances the expected signal contrast, compared to the commonly used scheme consisting of a series of π/2 and π pulses. We demonstrate further substantial increase of the robustness by using optimal control theory to identify splitting and swapping pulses that perform well on an ensemble average of pulse amplitudes and velocities. Our results demonstrate the ability of optimal control to significantly enhance future implementations of atomic fountain interferometry.

Cold-atom sources for the Matter-wave laser Interferometric Gravitation Antenna (MIGA)

The Matter-wave laser Interferometric Gravitation Antenna (MIGA) is an underground instrument using cold-atom interferometry to perform precision measurements of gravity gradients and strains. Following its installation at the low noise underground laboratory LSBB in the South-East of France, it will serve as a prototype for gravitational wave detectors with a horizontal baseline of 150 meters. Three spatially separated cold-atom interferometers will be driven by two common counter-propagating lasers to perform a measurement of the gravity gradient along this baseline. This article presents the cold-atom sources of MIGA, focusing on the design choices, the realization of the systems, the performances and the integration within the MIGA instrument.

Atom Interferometry with Floquet Atom Optics

Floquet engineering offers a compelling approach for designing the time evolution of periodically driven systems. We implement a periodic atom-light coupling to realize Floquet atom optics on the strontium ^{1}S_{0}-^{3}P_{1} transition. These atom optics reach pulse efficiencies above 99.4% over a wide range of frequency offsets between light and atomic resonance, even under strong driving where this detuning is on the order of the Rabi frequency. Moreover, we use Floquet atom optics to compensate for differential Doppler shifts in large momentum transfer atom interferometers and achieve state-of-the-art momentum separation in excess of 400  ℏk. This technique can be applied to any two-level system at arbitrary coupling strength, with broad application in coherent quantum control.

Atom Interferometer Driven by a Picosecond Frequency Comb

We demonstrate a light-pulse atom interferometer based on the diffraction of free-falling atoms by a picosecond frequency-comb laser. More specifically, we coherently split and recombine wave packets of cold ^{87}Rb atoms by driving stimulated Raman transitions between the |5s ^{2}S_{1/2},F=1⟩ and |5s ^{2}S_{1/2},F=2⟩ hyperfine states, using two trains of picosecond pulses in a counterpropagating geometry. We study the impact of the pulses' length as well as the interrogation time onto the contrast of the atom interferometer. Our experimental data are well reproduced by a numerical simulation based on an effective coupling that depends on the overlap between the pulses and the atomic cloud. These results pave the way for extending light-pulse interferometry to transitions in other spectral regions and therefore to other species, for new possibilities in metrology, sensing of gravito-inertial effects, and tests of fundamental physics.

Kapitza-Dirac Blockade: A Universal Tool for the Deterministic Preparation of Non-Gaussian Oscillator States

Harmonic oscillators count among the most fundamental quantum systems with important applications in molecular physics, nanoparticle trapping, and quantum information processing. Their equidistant energy level spacing is often a desired feature, but at the same time a challenge if the goal is to deterministically populate specific eigenstates. Here, we show how interference in the transition amplitudes in a bichromatic laser field can suppress the sequential climbing of harmonic oscillator states (Kapitza-Dirac blockade) and achieve selective excitation of energy eigenstates, cat states, and other non-Gaussian states. This technique can transform the harmonic oscillator into a coherent two-level system or be used to build a large-momentum-transfer beam splitter for matter waves. To illustrate the universality of the concept, we discuss feasible experiments that cover many orders of magnitude in mass, from single electrons over large molecules to dielectric nanoparticles.

Atomtronic Matter-Wave Lensing

In this Letter, we demonstrate magnetogravitational matter-wave lensing as a novel tool in atom-optics in atomtronic waveguides. We collimate and focus matter waves originating from Bose-Einstein condensates and ultracold thermal atoms in ring-shaped time-averaged adiabatic potentials. We demonstrate "delta-kick cooling" of Bose-Einstein condensates, reducing their expansion energies by a factor of 46 down to 800 pK. The atomtronic waveguide ring has a diameter of less than one millimeter, compared to other state-of-the-art experiments requiring zero gravity or free-flight distances of ten meters and more. This level of control with extremely reduced spatial requirements is an important step toward atomtronic quantum sensors.

Atom interferometry with quantized light pulses

The far-field patterns of atoms diffracted from a classical light field or from a quantum one in a photon-number state are identical. On the other hand, diffraction from a field in a coherent state, which shares many properties with classical light, displays a completely different behavior. We show that in contrast to the diffraction patterns, the interference signal of an atom interferometer with light-pulse beam splitters and mirrors in intense coherent states does approach the limit of classical fields. However, low photon numbers reveal the granular structure of light, leading to a reduced visibility since welcher-Weg (which-way) information is encoded into the field. We discuss this effect for a single photon-number state as well as a superposition of two such states.

Maximizing optical production of metastable xenon

The wide range of applications using metastable noble gas atoms has led to a number of different approaches for producing large metastable state densities. Here we investigate a recently proposed hybrid approach that combines RF discharge techniques with optical pumping from an auxiliary state in xenon. We study the effect of xenon pressure on establishing initial population in both the auxiliary state and metastable state via the RF discharge, and the role of the optical pumping beam power in transferring population between the states. We find experimental conditions that maximize the effects, and provide a robust platform for producing relatively large long-term metastable state densities.

Large Momentum Transfer Clock Atom Interferometry on the 689 nm Intercombination Line of Strontium

We report the first realization of large momentum transfer (LMT) clock atom interferometry. Using single-photon interactions on the strontium ^{1}S_{0}-^{3}P_{1} transition, we demonstrate Mach-Zehnder interferometers with state-of-the-art momentum separation of up to 141  ℏk and gradiometers of up to 81  ℏk. Moreover, we circumvent excited state decay limitations and extend the gradiometer duration to 50 times the excited state lifetime. Because of the broad velocity acceptance of the interferometry pulses, all experiments are performed with laser-cooled atoms at a temperature of 3  μK. This work has applications in high-precision inertial sensing and paves the way for LMT-enhanced clock atom interferometry on even narrower transitions, a key ingredient in proposals for gravitational wave detection and dark matter searches.

Bragg scattering from a millimeter-scale periodic structure with extremely small aspect ratios

The periodic structure on the optical surface affects the beam shape and its propagation. As the size of the optical elements becomes larger and its shape becomes complicated, the quantitative analysis of the effect of the periodic structure on the optical surface becomes indispensable given that it is very difficult to completely eliminate the microscopic periodic structures. Herein, we have experimentally investigated Bragg scattering from an optical surface with extremely small aspect ratios (~10^-5) and groove densities (0.5 lines/mm). We observed the period of the constructive interference formed due to the propagation of the 0th, 1st, and -1st beam modes caused by Bragg scattering. When the periodic structure has a modulation depth of ± 50 nm, the intensity increase of constructive interference between the beam modes formed by Bragg scattering was > 10 times greater than the intensity of a flat surface at the propagation distance at which constructive interference was most pronounced. This study is envisaged to open new avenues for the quantification of the effect of periodic structures based on the observation of the interference on the beam profile formed by Bragg scattering during the beam propagation.

Vortex conveyor belt for matter-wave coherent splitting and interferometry

We numerically study a matter wave interferometer realized by splitting a trapped Bose-Einstein condensate with phase imprinting. We show that a simple step-like imprinting pattern rapidly decays into a string of vortices that can generate opposite velocities on the two halves of the condensate. We first study in detail the splitting and launching effect of these vortex structures, whose functioning resembles the one of a conveyor belt, and we show that the initial exit velocity along the vortex conveyor belt can be controlled continuously by adjusting the vortex distance. We finally characterize the complete interferometric sequence, demonstrating how the phase of the resulting interference fringe can be used to measure an external acceleration. The proposed scheme has the potential to be developed into compact and high precision accelerometers.

Fast phase stabilization of a low frequency beat note for atom interferometry

Atom interferometry experiments rely on the ability to obtain a stable signal that corresponds to an atomic phase. For interferometers that use laser beams to manipulate the atoms, noise in the lasers can lead to errors in the atomic measurement. In particular, it is often necessary to actively stabilize the optical phase between two frequency components of the beams. Typically this is achieved using a time-domain measurement of a beat note between the two frequencies. This becomes challenging when the frequency difference is small and the phase measurement must be made quickly. The method presented here instead uses a spatial interference detection to rapidly measure the optical phase for arbitrary frequency differences. A feedback system operating at a bandwidth of about 10 MHz could then correct the phase in about 3 μs. This time is short enough that the phase correction could be applied at the start of a laser pulse without appreciably degrading the fidelity of the atom interferometer operation. The phase stabilization system was demonstrated in a simple atom interferometer measurement of the (87)Rb recoil frequency.

On-chip optical lattice for cold atom experiments

An atom-chip-based integrated optical lattice system for cold and ultracold atom applications is presented. The retroreflection optics necessary for forming the lattice are bonded directly to the atom chip, enabling a compact and robust on-chip optical lattice system. After achieving Bose-Einstein condensation in a magnetic chip trap, we load atoms directly into a vertically oriented 1D optical lattice and demonstrate Landau-Zener tunneling. The atom chip technology presented here can be readily extended to higher dimensional optical lattices.

A universal matter-wave interferometer with optical ionization gratings in the time-domain

Matter-wave interferometry with atoms¹ and molecules² has attracted a rapidly growing interest throughout the last two decades both in demonstrations of fundamental quantum phenomena and in quantum-enhanced precision measurements. Such experiments exploit the non-classical superposition of two or more position and momentum states which are coherently split and rejoined to interfere^3-11. Here, we present the experimental realization of a universal near-field interferometer built from three short-pulse single-photon ionization gratings^12,13. We observe quantum interference of fast molecular clusters, with a composite de Broglie wavelength as small as 275 fm. Optical ionization gratings are largely independent of the specific internal level structure and are therefore universally applicable to different kinds of nanoparticles, ranging from atoms to clusters, molecules and nanospheres. The interferometer is sensitive to fringe shifts as small as a few nanometers and yet robust against velocity-dependent phase shifts, since the gratings exist only for nanoseconds and form an interferometer in the time-domain.

102ℏk large area atom interferometers

We demonstrate atom interferometers utilizing a novel beam splitter based on sequential multiphoton Bragg diffractions. With this sequential Bragg large momentum transfer (SB-LMT) beam splitter, we achieve high contrast atom interferometers with momentum splittings of up to 102 photon recoil momenta (102ℏk). To our knowledge, this is the highest momentum splitting achieved in any atom interferometer, advancing the state-of-the-art by an order of magnitude. We also demonstrate strong noise correlation between two simultaneous SB-LMT interferometers, which alleviates the need for ultralow noise lasers and ultrastable inertial environments in some future applications. Our method is intrinsically scalable and can be used to dramatically increase the sensitivity of atom interferometers in a wide range of applications, including inertial sensing, measuring the fine structure constant, and detecting gravitational waves.

Experimental demonstration of a controllable electrostatic molecular beam splitter

We experimentally demonstrate a controllable electrostatic beam splitter for guided ND3 molecules with a single Y-shaped charged wire and a homogeneous bias field generated by a charged metallic parallel-plate capacitor. We study the dependences of the splitting ratio R of the guided ND3 beam and its relative guiding efficiency η on the voltage difference between two output arms of the splitter. The influences of the molecular velocity v and the cutting position L on the splitting ratio R are investigated as well, and the guiding and splitting dynamic processes of cold molecules are simulated. Our study shows that the splitting ratio R of our splitter can be conveniently adjusted from 10% to 90% by changing ΔU from -6  kV to +6  kV, and the simulated results are consistent with our experimental ones.

Enhancing the area of a Raman atom interferometer using a versatile double-diffraction technique

In this Letter, we demonstrate a new scheme for Raman transitions which realize a symmetric momentum-space splitting of 4 Planck's constant k, deflecting the atomic wave packets into the same internal state. Combining the advantages of Raman and Bragg diffraction, we achieve a three pulse state labeled an interferometer, intrinsically insensitive to the main systematics and applicable to all kinds of atomic sources. This splitting scheme can be extended to 4N Planck's constant k momentum transfer by a multipulse sequence and is implemented on a 8 Planck's constant k interferometer. We demonstrate the area enhancement by measuring inertial forces.

Noise-immune conjugate large-area atom interferometers

We present a pair of simultaneous conjugate Ramsey-Bordé atom interferometers using large (20variant Planck's over 2pik)-momentum transfer beam splitters, where variant Planck's over 2pik is the photon momentum. Simultaneous operation allows for common-mode rejection of vibrational noise. This allows us to surpass the enclosed space-time area of previous interferometers with a splitting of 20variant Planck's over 2pik by a factor of 2500. Using a splitting of 10variant Planck's over 2pik, we demonstrate a 3.4 ppb resolution in the measurement of the fine structure constant. Examples for applications in tests of fundamental laws of physics are given.

Atom interferometers with scalable enclosed area

Bloch oscillations (i.e., coherent acceleration of matter waves by an optical lattice) and Bragg diffraction are integrated into light-pulse atom interferometers with large momentum splitting between the interferometer arms, and hence enhanced sensitivity. Simultaneous acceleration of both arms in the same internal states suppresses systematic effects, and simultaneously running a pair of interferometers suppresses the effect of vibrations. Ramsey-Bordé interferometers using four such Bloch-Bragg-Bloch beam splitters exhibit 15% contrast at 24variant Planck's over 2pik splitting, the largest so far (variant Planck's over 2pik is the photon momentum); single beam splitters achieve 88variant Planck's over 2pik. The prospects for reaching 100 s of variant Planck's over 2pik and applications such as gravitational wave sensors are discussed.

Large momentum beam splitter using Bloch oscillations

The sensitivity of an inertial sensor based on an atomic interferometer is proportional to the velocity separation of atoms in the two arms of the interferometer. In this Letter we describe how Bloch oscillations can be used to increase this separation and to create a large momentum transfer (LMT) beam splitter. We experimentally demonstrate a separation of 10 recoil velocities. Light shifts during the acceleration introduce phase fluctuations which can reduce the fringes contrast. We precisely calculate this effect and demonstrate that it can be significantly reduced by using a suitable combination of LMT pulses. We finally show that this method seems to be very promising to realize a LMT beam splitter with several tens of recoils and a very good efficiency.

Atom interferometry with up to 24-photon-momentum-transfer beam splitters

We present up to 24-photon Bragg diffraction as a beam splitter in light-pulse atom interferometers to achieve the largest splitting in momentum space so far. Relative to the 2-photon processes used in the most sensitive present interferometers, these large momentum transfer beam splitters increase the phase shift 12-fold for Mach-Zehnder (MZ) and 144-fold for Ramsey-Bordé (RB) geometries. We achieve a high visibility of the interference fringes (up to 52% for MZ or 36% for RB) and long pulse separation times that are possible only in atomic fountain setups. As the atom's internal state is not changed, important systematic effects can cancel.

Thermal beam of metastable krypton atoms produced by optical excitation

A room-temperature beam of krypton atoms in the metastable 5s[3/2]2 level is demonstrated via an optical excitation method. A Kr-discharge lamp is used to produce vacuum ultraviolet photons at 124 nm for the first-step excitation from the ground level 4p6 1S0 to the 5s[3/2]1 level. An 819 nm Ti:sapphire laser is used for the second-step excitation from 5s[3/2]1 to 5s[3/2]2 followed by a spontaneous decay to the 5s[3/2]2 metastable level. A metastable atomic beam with an angular flux density of 3 x 10(14) s(-1) sr(-1) is achieved at the total gas flow rate of 0.01 cm3/s at STP (or 3 x 10(17) at./s). The dependences of the flux on the gas flow rate, laser power, and lamp parameters are investigated.

Atomic interferometer with amplitude gratings of light and its applications to atom based tests of the equivalence principle

We have developed a matter wave interferometer based on the diffraction of atoms from effective absorption gratings of light. In a setup with cold rubidium atoms in an atomic fountain the interferometer has been used to carry out tests of the equivalence principle on an atomic basis. The gravitational acceleration of the two isotopes 85Rb and 87Rb was compared, yielding a difference Deltag/g=(1.2+/-1.7)x10(-7). We also perform a differential free fall measurement of atoms in two different hyperfine states, and obtained a result of Deltag/g=(0.4+/-1.2)x10(-7).

Bragg scattering of free electrons using the Kapitza-Dirac effect

Bragg scattering has been observed for free electrons using a standing wave of light. Both the rocking curve and the angular electron distribution have been measured. The results of a numerical simulation to the Schrödinger equation are consistent with our experimental data. Unlike the diffraction regime which uses thin crystals, the Bragg regime requires the use of thick crystals. We point out several applications in atom optics that could be realized in electron optics.

Diffraction of complex molecules by structures made of light

We demonstrate that structures made of light can be used to coherently control the motion of complex molecules. In particular, we show diffraction of the fullerenes C(60) and C(70) at a thin grating based on a standing light wave. We prove experimentally that the principles of this effect, well known from atom optics, can be successfully extended to massive and large molecules which are internally in a thermodynamic mixed state and which do not exhibit narrow optical resonances. Our results will be important for the observation of quantum interference with even larger and more complex objects.

Large area light-pulse atom interferometry

We report the experimental demonstration of a large area atom interferometer based on extended sequences of light pulses. We characterize the interferometer through measurement of the acceleration due to gravity and demonstrate a threefold enhancement in intrinsic acceleration sensitivity. The technique is applicable to many atom interferometer configurations, including those used for measurement of rotations, gravity gradients, and Planck's over 2pi/m.

Imaging the phase of an evolving bose-einstein condensate wave function

We demonstrate a spatially resolved autocorrelation measurement with a Bose-Einstein condensate and measure the evolution of the spatial profile of its quantum mechanical phase. Upon release of the condensate from the magnetic trap, its phase develops a form that we measure to be quadratic in the spatial coordinate. Our experiments also reveal the effects of the repulsive interaction between two overlapping condensate wave packets and we measure the small momentum they impart to each other.

Generating solitons by phase engineering of a bose-einstein condensate

Quantum phase engineering is demonstrated with two techniques that allow the spatial phase distribution of a Bose-Einstein condensate (BEC) to be written and read out. A quantum state was designed and produced by optically imprinting a phase pattern onto a BEC of sodium atoms, and matter-wave interferometry with spatially resolved imaging was used to analyze the resultant phase distribution. An appropriate phase imprint created solitons, the first experimental realization of this nonlinear phenomenon in a BEC. The subsequent evolution of these excitations was investigated both experimentally and theoretically.

Phase-coherent amplification of matter waves

Phase-coherent matter-wave amplification was demonstrated using Bose- Einstein-condensed rubidium-87 atoms. A small seed matter wave was created with coherent optical Bragg diffraction. Amplification of this seed matter wave was achieved by using the initial condensate as a gain medium through the superradiance effect. The coherence properties of the amplified matter wave, studied with a matter-wave interferometer, were shown to be locked to those of the initial seed wave. The active matter-wave device demonstrated here has great potential in the fields of atom optics, atom lithography, and precision measurements.