Atom Interferometry Research Articles

Robust double Bragg diffraction via detuning control

We present a theoretical model and numerical optimization of double Bragg diffraction, a widely used technique in atom interferometry. We derive an effective two-level-system Hamiltonian based on the Magnus expansion in the so-called quasi-Bragg regime, where most Bragg-pulse atom interferometers operate. Furthermore, we extend the theory to a five-level description to account for Doppler detuning. Using these derived effective Hamiltonians, we investigate the impacts of AC-Stark shift and polarization errors on the double Bragg beam splitter, along with their mitigations through detuning control. Notably, we design a linear detuning sweep that demonstrates robust efficiency exceeding 99.5% against polarization errors up to 8.5%. Moreover, we develop an artificial-intelligence-aided optimal detuning control protocol, showcasing enhanced robustness against both polarization errors and Doppler effects. This protocol achieves an average efficiency of 99.92% for samples with a finite momentum width of 0.05ℏkL within an extended polarization error range of up to 10%. Published by the American Physical Society 2024

Quantum Gravimetry for Future Satellite Gradiometry

The present electrostatic accelerometers (EA) drift at low frequencies. To address this problem, integrating a cold atom interferometry (CAI) accelerometer could be beneficial, as it offers the potential for superior long-term stability. The CAI-based accelerometers (CAI ACC) are accurate and stable, but they have some issues with long dead times and a relatively small dynamic range. A way to address these problems is to combine a CAI ACC with an EA in a hybrid configuration. Using CAI ACC in an upcoming satellite gradiometry mission can give stable and accurate measurements of the static Earth’s gravity field. Three scenarios have been considered in this study: first, a realistic scenario involving current-generation and realistic hybrid accelerometers; second, a semi-realistic scenario with the same accelerometers and an accurate gyroscope; and third, using highly accurate hybrid/CAI accelerometers with an optimistic gyroscope. One significant aspect was on detecting temporal gravity changes, which cannot compare to the effectiveness of the low-low satellite-to-satellite tracking (LLSST) principle. But, quantum gradiometers can significantly enhance solutions for the static gravity field, provided one has accurate observations of the satellite orientation available.

Optimal Floquet state engineering for large scale atom interferometers

The effective control of atomic coherence with cold atoms has made atom interferometry an essential tool for quantum sensors and precision measurements. The performance of these interferometers is closely related to the operation of large wave packet separations. We present here a novel approach for atomic beam splitters based on the stroboscopic stabilization of quantum states in an accelerated optical lattice. The corresponding Floquet state is generated by optimal control protocols. In this way, we demonstrate an unprecedented Large Momentum Transfer (LMT) interferometer, with a momentum separation of 600 photon recoils (600 ℏk) between its two arms. Each LMT beam splitter is realized in a remarkably short time (2 ms) and is highly robust against the initial velocity dispersion of the wave packet and lattice depth fluctuations. Our study shows that Floquet engineering is a promising tool for exploring new frontiers in quantum physics at large scales, with applications in quantum sensing and testing fundamental physics.

Impact of the π-pulse shape on the contrast of thermal Atom Interferometers

Abstract The key role of π- and π/2-pulses in atom interferometry has been widely recognized as their efficiency affect the overall performance of atomic interferometers. The inefficiencies are evident when using thermal cloud atoms as the field interaction does not compensate for the atom velocity. Temporal pulse shaping offers a solution to this issue by balancing the effect of the temporal shape of the mirror pulse in thermal cold atom interferometry by testing pulse shapes beyond the standard rectangle including Gaussian-like, Sinc-like, optimized Band-selective Uniform Response Pure-phase family, and optimized Gaussian Cascade family. We unveiled a correlation between the π-pulse fidelity and the overall interferometer contrast function. We also found robust pulse sequences with respect to initial atom velocities that offer contrast as high as 0.7 compared to standard rectangle sequences with values of 0.2. The investigated pulse sequences offer an efficient way to improve the performance of atom interferometers, increasing the potential of thermal cold atom interferometry.

Reinforcement learning for rotation sensing with ultracold atoms in an optical lattice

In this paper, we investigate a design approach of reinforcement learning to engineer a gyroscope in an optical lattice for the inertial sensing of rotations. Our methodology is not based on traditional atom interferometry, that is, splitting, reflecting, and recombining wavefunction components. Instead, the learning agent is assigned the task of generating lattice shaking sequences that optimize the sensitivity of the gyroscope to rotational signals in an end-to-end design philosophy. What results is an interference device that is completely distinct from the familiar Mach-Zehnder-type interferometer. For the same total interrogation time, the end-to-end design leads to a twentyfold improvement in sensitivity over traditional Bragg interferometry. Published by the American Physical Society 2024

Constraint on an Exotic Parity-Odd Spin- and Velocity-Dependent Interaction with Atom Interferometer.

We present a high-precision atom-interferometric test of the parity-odd spin- and velocity-dependent (SVD) interaction between the spin-polarized proton and unpolarized nucleons. The test utilizes the Bragg atom interferometer loaded with ^{87}Rb atoms, of which the single unpaired proton within the nuclei plays the role of the test spin. The differential measurement of the acceleration of the atom in two well-chosen inner states is designed to eliminate the influence from the polarized electron in the ^{87}Rb atom. Moreover, the atom interferometer is particularly placed in the cave laboratory within the Yujia Mountain in the campus, and the mountain source of unpolarized nucleons allows to improve test of the SVD on the length scale around 5-100m. Our experiment improves the test precision of the universality of free fall to 9.2×10^{-9}, which is about 10 times better than the previous experiment with polarized atoms. More importantly, it provides a new constraint on the coupling of the SVD interaction exerting to the spin-polarized proton |g_{A}^{p}g_{V}^{N}|≤6.5×10^{-32} at λ=10 m, resulting in a substantial sensitivity improvement over the previous limit. Our work extends the scope of atom interference measurements and shines a new light on the testing of new physics with polarized-atom interferometers.

Novel atom interferometer may become an astronomical asset

Improving terrestrial gravitational wave detection with “multi-loop” geometry

A scalable, symmetric atom interferometer for infrasound gravitational wave detection

We propose a terrestrial detector for gravitational waves with frequencies between 0.3 and 5 Hz based on atom interferometry. As key elements, we discuss two symmetric matter-wave interferometers, the first one with a single loop and the second one featuring a folded triple-loop geometry. The latter eliminates the need for atomic ensembles at femtokelvin energies imposed by the Sagnac effect in other atom interferometric detectors. The folded triple-loop geometry also combines several advantages of current vertical and horizontal matter wave antennas and enhances the scalability in order to achieve a peak strain sensitivity of 2×10−21/Hz.

Sub-Hz fundamental, sub-kHz integral linewidth self-injection locked 780 nm hybrid integrated laser

Today’s precision experiments for timekeeping, inertial sensing, and fundamental science place strict requirements on the spectral distribution of laser frequency noise. Rubidium-based experiments utilize table-top 780 nm laser systems for high-performance clocks, gravity sensors, and quantum gates. Wafer-scale integration of these lasers is critical for enabling systems-on-chip. Despite progress towards chip-scale 780 nm ultra-narrow linewidth lasers, achieving sub-Hz fundamental linewidth and sub-kHz integral linewidth has remained elusive. Here we report a hybrid integrated 780 nm self-injection locked laser with 0.74 Hz fundamental and 864 Hz integral linewidths and thermorefractive-noise-limited 100 Hz2/Hz at 10 kHz. These linewidths are over an order of magnitude lower than previous photonic-integrated 780 nm implementations. The laser consists of a Fabry-Pérot diode edge-coupled to an on-chip splitter and a tunable 90 million Q resonator realized in the CMOS foundry-compatible silicon nitride platform. We achieve 2 mW output power, 36 dB side mode suppression ratio, and a 2.5 GHz mode-hop-free tuning range. To demonstrate the potential for quantum atomic applications, we analyze the laser noise influence on sensitivity limits for atomic clocks, quantum gates, and atom interferometer gravimeters. This technology can be translated to other atomic wavelengths, enabling compact, ultra-low noise lasers for quantum sensing, computing, and metrology.

Single-photon large-momentum-transfer atom interferometry scheme for Sr or Yb atoms with application to determining the fine-structure constant

The leading experimental determinations of the fine-structure constant α currently rely on atomic photon-recoil measurements from Ramsey-Bordé atom interferometry with large-momentum transfer to provide an absolute mass measurement. We propose an experimental scheme for an intermediate-scale differential atom interferometer to measure the photon recoil of neutral atomic species with a single-photon optical clock transition. We calculate trajectories for our scheme that optimize the recoil phase while nullifying the undesired gravity-gradient phase by considering independently launching two clouds of ultracold atoms with the appropriate initial conditions. For Sr and Yb, we find an atom interferometer of height 3 m to be sufficient for an absolute mass measurement precision of Δm/m∼1×10−11 with current technology. Such a precise measurement would halve the current uncertainty in α, an uncertainty that would no longer be limited by an absolute mass measurement. The removal of this limitation would allow the current uncertainty in α to be reduced by a factor of 10 by corresponding improvements in relative mass measurements, thus paving the way for higher-precision tests of the standard model of particle physics. Published by the American Physical Society 2024

Noise assessment of cold atom interferometry gradiometry observations

Over the past few decades, the development of interferometric techniques utilizing cold atoms has significantly advanced, particularly in the realm of gravimetry. This paper explores the characterization of noise within atomic gradiometry systems, which is essential for enhancing measurement accuracy as new methodologies and tools are introduced. Specifically, we examine the noise components using advanced techniques such as least squares component estimation and Allan variance analysis. Applying these sophisticated methods to two distinct datasets, our results robustly indicate that white noise is the predominant and most resilient type of noise in gravity gradiometry measurements based on atomic interferometry, with variances of σP12=2.97×10−8 for dataset 1 and σP22=5.66×10−7 for dataset 2. The predominance of white noise simplifies the system dynamics and enhances the reliability of the estimation methods. Furthermore, our calculations yield an uncertainty in the gravity gradient resolution of σ Γ1 = 0.13 E (where 1 E = 10−9 s−2) and σ Γ2 = 3.55 E over time, underscoring the high precision achievable with current interferometric techniques.

Dynamic instabilities and turbulence of merged rotating Bose–Einstein condensates

We present the simulation results of merging harmonically confined rotating Bose–Einstein condensates in two dimensions. Merging of the condensate is triggered by positioning the rotation axis at the trap minima and moving both condensates toward each other while slowly ramping their rotation frequency. We analyze the dynamics of the merged condensate by letting them evolve under a single harmonic trap. We systematically investigate the formation of solitonic and vortex structures in the final, unified condensate, considering both nonrotating and rotating initial states. In both cases, merging leads to the formation of solitons that decay into vortex pairs through snake instability, and subsequently, these pairs annihilate. Soliton formation and decay-induced phase excitations generate sound waves, more pronounced when the merging time is short. We witness no sound wave generation at sufficiently longer merging times that finally leads to the condensate reaching its ground state. With rotation, we notice off-axis merging (where the rotation axes are not aligned), leading to the distortion and weakening of soliton formation. The incompressible kinetic energy spectrum exhibits a Kolmogorov-like cascade [E(k)∼k−5/3] in the initial stage for merging condensates rotating above a critical frequency and a Vinen-like cascade [E(k)∼k−1] at a later time for all cases. Our findings hold potential significance for atomic interferometry, continuous atomic lasers, and quantum sensing applications.

Quantum sensing of acceleration and rotation by interfering magnetically launched atoms.

Accurate and stable measurement of inertial quantities is essential in geophysics, geodesy, fundamental physics, and inertial navigation. Here, we present an architecture for a compact cold-atom accelerometer-gyroscope based on a magnetically launched atom interferometer. Characterizing the launching technique, we demonstrate 700-parts per million gyroscope scale factor stability over 1 day, while acceleration and rotation rate bias stabilities of 7 × 10-7 meters per second squared and 4 × 10-7 radians per second are reached after 2 days of integration of the cold-atom sensor. Hybridizing it with a classical accelerometer and gyroscope, we correct their drift and bias to achieve respective 100-fold and 3-fold increase on the stability of the hybridized sensor compared to the classical ones. Compared to a state-of-the-art atomic gyroscope, the simplicity and scalability of our launching technique make this architecture easily extendable to a compact full six-axis inertial measurement unit, providing a pathway toward autonomous positioning and orientation using cold-atom sensors.

Ultralight scalar and axion dark matter detection with long-baseline atom interferometers

Abstract The detection of dark matter is a challenging problem in modern physics. We provide a proposal to detect the coupling of ultralight scalar dark matter to quarks and gluons as well as the coupling of ultralight axion dark matter to gluons with long-baseline atom interferometers. The ultralight scalar and axion dark matter could induce the oscillation of the nuclear charge radii and then oscillate the atomic transition frequency by interacting with quarks and gluons. We calculate the differential phase shift caused by the scalar and axion dark matter in long-baseline atom interferometers and give the proposed constraints on the scalar dark matter coupling parameters $d_g$ and $d_{\hat{m}}$ as well as the axion dark matter coupling parameter $1/f_a$. Our results are expected to improve existing bounds and complement bounds from other experiments in the future.

Digital stabilization of an I/Q modulator in the carrier suppressed single-sideband mode for atom interferometry

We present an all-digital method for stabilizing the phase biases in an electro-optic I/Q modulator for carrier-suppressed single-sideband (CS-SSB) modulation. Using programmable logic on the Red Pitaya STEMlab 125-14 platform, we digitally generate and demodulate an auxiliary radio-frequency tone whose beat with the optical carrier probes the I/Q modulator’s phase imbalances. We implement a multiple-input, multiple-output integral feedback controller that accounts for unavoidable cross-couplings in the phase biases to lock the error signals at exactly zero, where optical power fluctuations have no impact on phase stability. We demonstrate >23dB suppression of the optical carrier relative to the desired sideband at +3.4GHz over a period of 15 h and over temperature variations of 20°C.

Limits on the sensitivity of a cold atom interferometry gyroscope

Limits on the sensitivity of a cold atom interferometry gyroscope

Black hole spectroscopy with ground-based atom interferometer and space-based laser interferometer gravitational wave detectors

Gravitational wave (GW) detection allows us to test general relativity in entirely new regimes. A prominent role takes the detection of quasi-normal modes (QNMs), which are emitted after the merger of a binary black hole (BBH) when the highly distorted remnant emits GWs to become a regular Kerr black hole (BH). The BH uniqueness theorems of Kerr black hole solutions in general relativity imply that the frequencies and damping times of QNMs are determined solely by the mass and spin of the remnant BH. Therefore, detecting QNMs offers a unique way to probe the nature of the remnant BH and to test general relativity. We study the detection of a merging BBH in the intermediate-mass range, where the inspiral–merger phase is detected by space-based laser interferometer detectors TianQin and LISA, while the ringdown is detected by the ground-based atom interferometer (AI) observatory AION. The analysis of the ringdown is done using the regular broadband mode of AI detectors as well as the resonant mode optimizing it to the frequencies of the QNMs predicted from the inspiral–merger phase. We find that the regular broadband mode allows constraining the parameters of the BBH with relative errors of the order 10−1 and below from the ringdown. Moreover, for a variety of systems considered, the frequencies and the damping times of the QNMs can be determined with relative errors below 0.1 and 0.2, respectively. We further find that using the resonant mode can improve the parameter estimation for the BBH from the ringdown by a factor of up to three. Utilizing the resonant mode significantly limits the detection of the frequency of the QNMs but improves the detection error of the damping times by around two orders of magnitude.

Optical frequency filtering for Raman beams.

We present an optical filter that is appropriate for use with Raman beams in atomic interferometry. This is a filter that lets the light of the two frequencies of the Raman pair go through and rejects spurious frequencies that may be close to the atomic resonance and cause decoherence. We characterized the filter's performance optically and also by shining the light into atoms in a Ramsey sequence, to look for decoherence effects from photon scattering. We found that it is safe to use tapered amplifiers in single and double pass for light amplification in the Raman beams since the pedestal of emission has a negligible effect, which can be further reduced by the use of the filter we present.

Perspective on Quantum Sensors from Basic Research to Commercial Applications

Quantum sensors represent a new generation of sensors with improved precision, accuracy, stability, and robustness to environmental effects compared to their classical predecessors. After decades of laboratory development, several types of quantum sensors are now commercially available or are part-way through the commercialization process. This paper provides a brief description of the operation of a selection of quantum sensors that employ the principles of atom–light interactions and discusses progress toward packaging those sensors into products. This paper covers quantum inertial and gravitational sensors, including gyroscopes, accelerometers, gravimeters, and gravity gradiometers that employ atom interferometry, nuclear magnetic resonance gyroscopes, atomic and spin-defect magnetometers, and Rydberg electric field sensors.

Determining the tilt of the Raman laser beam using an optical method for atom gravimeters

Abstract The tilt of Raman laser is a major systematic error in precision gravity measurement using atom interferometry. The conventional approach to evaluate this tilt error involves modulating the direction of the Raman laser and conducting time-consuming gravity measurements to identify the error minimum. In this work, we demonstrate a method to expediently determine the tilt of the Raman laser by transforming tilt angle measurement into parallelism characterization, which integrates the optical method of aligning the laser direction, commonly used in freely-falling corner-cube gravimeters, into atom gravimeters. A position sensing detector (PSD) is utilized to quantitatively characterize the parallelism between the test beam and the reference beam, thus measuring the tilt precisely and rapidly. After carefully positioning the PSD and calibrating the relationship between the distance measured by the PSD and the tilt angle measured by tiltmeter, we achieved a statistical uncertainty of less than 30 μrad in the tilt measurement. Furthermore, we compared the results obtained through this optical method with those from the conventional gravity measurement tilt modulation method. The comparison validates that our optical method can achieve tilt determination with an accuracy level of better than 200 μrad，corresponding to a systematic error of 20 μGal in g measurement. This work has practical implications for real world applications of atom gravimeters.