Atom interferometers employing optical cavities to enhance the beam splitter pulses promise significant advances in science and technology, notably for future gravitational wave detectors. Long cavities, on the scale of hundreds of meters, have been proposed in experiments aiming to become demonstrators for gravitational wave detection at frequencies below 1 Hz, where laser interferometers, such as LIGO, have poor sensitivity. Our group at the Birmingham Institute of Gravitational Wave Astronomy has explored the fundamental limitations of two-mirror cavities for atomic beam splitting, and established upper bounds on the temperature of the atomic ensemble as a function of cavity length and three design parameters: the cavity $g$-factor, the bandwidth, and the optical suppression factor of the first and second order spatial modes. A lower bound to the cavity bandwidth which avoids elongation of the interaction time and maximizes power enhancement was found. An upper limit to cavity length is also found for symmetric two-mirror cavities. These key limitations impact the feasibility of long-baseline detectors, which suffer from a naturally larger bandwidth and worse optical suppression of higher order optical modes. Our findings will aid the design of current and future experiments using this technology, such as the MIGA experiment in Bordeaux. In the future we aim to fully model the effect that the imperfect optical wavefronts have on the atomic transitions.
Atom interferometers employing optical cavities to enhance the beam splitter pulses promise significant advances in science and technology, notably for future gravitational wave detectors. Long cavities, on the scale of hundreds of meters, have been proposed in experiments aiming to become demonstrators for gravitational wave detection at frequencies below 1 Hz, where laser interferometers, such as LIGO, have poor sensitivity. Our group at the Birmingham Institute of Gravitational Wave Astronomy has explored the fundamental limitations of two-mirror cavities for atomic beam splitting, and established upper bounds on the temperature of the atomic ensemble as a function of cavity length and three design parameters: the cavity g-factor, the bandwidth, and the optical suppression factor of the first and second order spatial modes. A lower bound to the cavity bandwidth which avoids elongation of the interaction time and maximizes power enhancement was found. An upper limit to cavity length is also found for symmetric two-mirror cavities. These key limitations impact the feasibility of long-baseline detectors, which suffer from a naturally larger bandwidth and worse optical suppression of higher order optical modes. Our findings will aid the design of current and future experiments using this technology, such as the MIGA experiment in Bordeaux. In the future we aim to fully model the effect that the imperfect optical wavefronts have on the atomic transitions.
Atom interferometers employing optical cavities to enhance the beam splitter pulses promise significant advances in science and technology, notably for future gravitational wave detectors. Long cavities, on the scale of hundreds of meters, have been proposed in experiments aiming to observe gravitational waves with frequencies below 1 Hz, where laser interferometers, such as LIGO, have poor sensitivity. Alternatively, short cavities have also been proposed for enhancing the sensitivity of more portable atom interferometers.We explore the fundamental limitations of two-mirror cavities for atomic beam splitting, and establish upper bounds on the temperature of the atomic ensemble as a function of cavity length and three design parameters: the cavity g factor, the bandwidth, and the optical suppression factor of the first and second order spatial modes. A lower bound to the cavity bandwidth is found which avoids elongation of the interaction time and maximizes power enhancement. An upper limit to cavity length is found for symmetric two-mirror cavities, restricting the practicality of long baseline detectors. For shorter cavities, an upper limit on the beam size was derived from the geometrical stability of the cavity. These findings aim to aid the design of current and future cavity-assisted atom interferometers.
Atom interferometers employing optical cavities to enhance the beam splitter pulses promise significant advances in science and technology, notably for future gravitational wave detectors. Long cavities, on the scale of hundreds of meters, have been proposed in experiments aiming to observe gravitational waves with frequencies below 1 Hz, where laser interferometers, such as LIGO, have poor sensitivity. Alternatively, short cavities have also been proposed for enhancing the sensitivity of more portable atom interferometers. We explore the fundamental limitations of two-mirror cavities for atomic beam splitting, and establish upper bounds on the temperature of the atomic ensemble as a function of cavity length and three design parameters: the cavity g factor, the bandwidth, and the optical suppression factor of the first and second order spatial modes. A lower bound to the cavity bandwidth is found which avoids elongation of the interaction time and maximizes power enhancement. An upper limit to cavity length is found for symmetric two-mirror cavities, restricting the practicality of long baseline detectors. For shorter cavities, an upper limit on the beam size was derived from the geometrical stability of the cavity. These findings aim to aid the design of current and future cavity-assisted atom interferometers.
This report presents the results of the 2012-2013 NASA Institute for Advanced Concepts (NIAC) Phase 1 Atom Interferometry for Detection of Gravitational Waves project. The origin of this GW (Gravitational Wave) detection concept using atoms can be traced to theoretical work that first appeared in 2008 and also to a satellite mission-focused followup study that was done in 2011. The goal of the current project was to explore both theoretical and technical issues surrounding the implementation of this idea, as well as to begin performing proof-of-concept experiments to validate critical aspects of the proposal.The top level trade space for the detector design is driven by the strategy employed to mitigate laser frequency noise, which, if uncontrolled, can mask GW signatures. One of the advantages of the atom interferometric approach is the possibility of single baseline detection (Fig. 1.1), even in the presence of laser noise. This is enabled by the differential measurement between the two ensembles of atoms, which can result in substantial laser noise suppression. The details of this suppression depend on the atomic physics techniques used to implement the atom interferometry. Specifically, we considered the effect on noise suppression that results from using traditional two-photon Raman transitions (with alkali atoms) and also single-photon transitions (with alkaline earth-like atoms).The interferometers shown in Fig 1.1(b) take advantage of single-photon transitions (as opposed to traditional Raman transitions) because using light pulses from one direction at a time allows for near perfect common-mode cancellation of laser phase noise, even for long baselines. This calls for the use of atomic transitions with an (ideally large) optical energy level difference with a long (greater than 1 second) lifetime, such as high-transitions routinely used for optical atomic clocks in species like Sr, Ca and Yb. Notably, large momentum transfer (LMT) atom optics - and the sensitivity enhancement they confer – can still be realized by simply adding additional pairs of alternating pulses to each beam splitter process. Section 3 reports on the theoretical work we performed to justify this GW detection protocol using single-photon transitions. This approach represents a new method for GW detection using atoms that is distinct from the original proposal from 2008. At the system level, we evaluated three architectures, each of which implements a different solution to the laser frequency noise issue. The first two designs are based on two-photon Raman transitions with Rb atoms. One of these is a three-satellite, multiple baseline design while the other is a two-satellite, single baseline design. The third proposal is a two-satellite, single baseline design that uses single-photon transitions with Sr atoms. These three architectures are described in more detail in Section 2. There are a number of known technical issues that we have started to address using ground-based experiments. These issues include atom technology development needs such as, for example, lower ensemble temperature requirements and large momentum transfer (LMT) atom optics. To this end, we have built a 10-meter scale atom drop tower, where we can perform proof-of-principle demonstrations of the proposed AGIS detector in an environment that permits more than 2.5 seconds of free-fall time. This facility allows for demonstration of atom interferometry with long interrogation time (seconds) and large atom wavepacket
Abstract Large-scale atom interferometers promise unrivaled strain sensitivity to mid-band gravitational waves, and will probe a new parameter space in the search for ultra-light scalar dark matter. These proposals require gradiometry with kilometer-scale baselines, a momentum separation above 104ℏk between interferometer arms, and optical transitions to long-lived clock states to reach the target sensitivities. Prohibitively high optical power and wavefront flatness requirements have thus far limited the maximum achievable momentum splitting. Here we propose a scheme for optical cavity enhanced atom interferometry, using circulating, spatially resolved pulses, and intracavity frequency modulation to meet these requirements. We present parameters for the realization of 20 kW circulating pulses in a 1 km interferometer enabling 104ℏk splitting on the 698 nm clock transition in 87Sr. This scheme addresses the presently insurmountable laser power requirements and is feasible in the context of a kilometer-scale atom interferometer facility.
Atom interferometry is a maturing quantum technology which provides one of the most precise approaches to explore fundamental physics, e.g. to search for dark matter, and one day to observe gravitational waves in the frequency range from 10 mHz - 10 Hz. Standard atom interferometers use Bragg or Raman two-photon transitions for the coherent manipulation of matter waves. In a Michelson configuration for atom-aided gravitational waves detection, two orthogonal arms are built to reject laser noise, in the same way as optical interferometers. Atom interferometers utilizing an optical clock transition for coherent manipulation are less affected by the technical noise of the laser, and as a result that single baseline detectors become feasible.At LP2N, we are building a vertical gravity-gradiometer based on atom interferometry using strontium atoms probed on such a clock transition. The final experimental setup will implement a 6-meter tall atomic fountain to realize gradiometry with two or more separated atomic clouds.In my dissertation, I present the realization of the experimental setup in all its sub-systems, and the first experiments with atoms at millikelvin temperature obtained with the first cooling stage with blue light. The laser system for the second red cooling phase and for the coherent manipulation is ready; meanwhile, we realized a dual-frequency Zeeman slower that improves the atomic flux by a factor of six. We also present a study of an original scheme to achieve pulsed and fast light-atom interaction in a narrow-linewidth cavity by exploiting the Stark shift as a high bandwidth switch; this technique could open to the use of narrow-linewidth cavities – and notably their high power buildup - in several contexts, like atom interferometry and quantum information.
Abstract Currently planned and constructed terrestrial detectors for gravitational waves and dark matter based on differential light-pulse atom interferometry are designed around three primary strategies to enhance their sensitivity: (i) Resonant-mode enhancement using multiple diamonds, (ii) large-momentum-transfer (LMT) techniques to increase arm separation within the interferometer, and (iii) very-long baseline schemes that increase the distance between the two interferometers. Both resonant-mode enhancement and LMT techniques result in a greater number of light pulses, making high pulse fidelity during atom-light interactions imperative. At the same time, increasing the number of diamonds in vertical configurations leads to taller atomic fountains, which consequently reduces the available distance between interferometers. As a result, the number of diamonds, LMT pulses, and the fountain height are interdependent parameters that must be carefully balanced. In this work, we present optimal configurations for multi-diamond geometries in resonant mode, explicitly accounting for the spatial extent of a single interferometer, considering constraints imposed by the baseline dimensions and atomic losses due to imperfect pulses. For this optimization, we numerically scan the relevant parameters such as initial position and momentum of the atomic cloud, transferred momenta, and number of loops. For each parameter set, we verify whether the imposed conditions are met and evaluate the resulting sensitivities to identify optimal configurations. We provide practical analytical relations to estimate the optimal number of pulses that should be applied. Many proposals beyond demonstrator experiments require pulse numbers that demand efficiencies not yet demonstrated with state-of-the-art momentum transfer techniques. As a result, the observed sensitivity falls short of expectations—an effect caused by both arm separation and atom loss per pulse—highlighting the urgent need for research aimed at improving pulse fidelities.