We examine the prospects of utilizing matter-wave Fabry-Pérot interferometers for enhanced inertial sensing applications. Our study explores such tunneling-based sensors for the measurement of accelerations in two configurations: (a) a transmission setup, where the initial wave packet is transmitted through the cavity and (b) an out-tunneling scheme with intra-cavity generated initial states lacking a classical counterpart. We perform numerical simulations of the complete dynamics of the quantum wave packet, investigate the tunneling through a matter-wave cavity formed by realistic optical potentials and determine the impact of interactions between atoms. As a consequence we estimate the prospective sensitivities to inertial forces for both proposed configurations and show their feasibility for serving as inertial sensors.
We examine the prospects of utilizing matter-wave Fabry-Pérot interferometers for enhanced inertial sensing applications. Our study explores such tunneling-based sensors for the measurement of accelerations in two configurations: (a) a transmission setup, where the initial wave packet is transmitted through the cavity and (b) an out-tunneling scheme with intra-cavity generated initial states lacking a classical counterpart. We perform numerical simulations of the complete dynamics of the quantum wave packet, investigate the tunneling through a matter-wave cavity formed by realistic optical potentials and determine the impact of interactions between atoms. As a consequence we estimate the prospective sensitivities to inertial forces for both proposed configurations and show their feasibility for serving as inertial sensors.
The present cumulative thesis (Publications (I)–(III) [1– 3]) explores three complementary directions: (i) tunneling-based gravimetry, (ii) phase contributions of tunneled Ramsey clocks, and (iii) resource optimization for very-long-baseline atom interferometers designed for the detection of gravitational waves and dark matter. The development of atom interferometers and atomic clocks seeks to steadily increase the measurement sensitivity, with the ultimate bound set by the Heisenberg limit. Enhancements can be achieved by exploiting quantum phenomena such as entanglement and squeezing, which allow sensitivities below the shot-noise limit. Another fundamental quantum effect, tunneling, remains less explored in the context of metrology, despite its inherent quantum nature. While entanglement and squeezing have already been demonstrated in atom interferometers, tunneling has not yet been widely investigated for gravimetric sensing applications. Publication (I) explores two configurations of tunneling-based gravimeters using a matter-wave Fabry–Pérot interferometer. (i) In the transmission setup, the wave packet is prepared in front of the cavity generated by optical potentials and transmitted. (ii) In the tunneling setup, the wave packet is prepared inside the cavity, representing a configuration without a classical analogue. Through our numerical simulations of the wave packet dynamics, including gravitational effects, we find that gravity primarily alters the motion of the packet by accelerating, decelerating, and deforming it, which modifies in particular its width at impact. While a single Gaussian barrier shows no resonances, the Fabry–Pérot configuration supports multiple resonances, defining tunable working points and acting as a velocity filter. In Publication (II), we turn to the phase accumulated during tunneling, investigated via a Ramsey clock. The Ramsey clock consists of a superposition of two internal states, accumulating a phase that is read out via a Ramsey sequence. Adopting an operational definition where time is what you read off a clock, we identify a tunneling time associated with the tunneling phase, alongside relativistic contributions accumulated by the tunneled clock. This approach naturally unifies several conventional definitions of tunneling time. Furthermore, the tunneling phase can be amplified experimentally by introducing state-dependent barrier heights through differential light shifts. In Publication (III), we study differential geometries of terrestrial very-long baseline atom interferometers, currently in development for gravitational-wave and dark-matter detection. We analyze three strategies for signal enhancement: (i) large-momentum-transfer pulses to increase atom–light interaction points, (ii) resonant-mode enhancement by matching the interrogation time to the target frequency, and (iii) extending baseline lengths. The achievable number of pulses is limited by atomic losses, distributed between large-momentum-transfer sequences and number of diamonds. Additionally, more diamonds require taller atomic fountains, constrained by the finite baseline. Thus, a trade-off emerges between the number of large-momentum-transfer pulses, the number of diamonds, and the baseline length. Considering this interplay, we derive an analytical relation for the optimal number of pulses under given loss rates. We explicitly optimize the allocation of the available resources and account for the finite spatial extent of individual interferometers, baseline constraints, and atom loss from imperfect pulses.
Over the past two decades there has been considerable and growing interest in the development of quantum sensors. These are devices whose function is based on quantum systems and offer the potential for unprecedented sensitivity in a range of measurements. This PhD has developed three different theoretical projects examining the sensitivity improvement of these devices with a focus on atom gravimeters, which are particularly useful for measuring inertial quantities such as rotations and accelerations. We have investigated the theoretical sensitivity limits of atom gravimeters and we examined different entanglement-enhanced schemes, in order to increase their performance. To start with, we used tools from estimation theory, in order to quantify the performance of current atom gravimeters. We showed that there is additional metrological potential in these devices, and that we can extract all this information by making innovative measurements, other than the conventional population difference measurement. Our analysis introduces a new way of evaluating the performance of atom gravimeters that could influence future sensor designs. In addition, we examined entanglement-enhanced schemes, in order to improve the performance of quantum sensors, which are limited by the atom shot-noise limit. We considered entanglement generation schemes based on atom-light interactions, in order for them to be compatible with atom interferometer based sensors. More particularly, we examined a quantum non-demolition measurement scheme and an one-axis-twisting scheme with cavity feedback. In both schemes we incorporated relevant decoherence mechanisms and we analysed how the optimum parameter regime can be found, by balancing between coherence loss and spin-squeezing strength. We also examined several modifications in both models that could offer additional improvements. The results presented here could have a big impact on the future design and understanding of atom-based quantum-enhanced sensors.
Abstract The past few decades have seen dramatic progress in our ability to manipulate and coherently control matter-waves. Although the duality between particles and waves has been well tested since de Broglie introduced the matter-wave analog of the optical wavelength in 1924, manipulating atoms with a level of coherence that enables one to use these properties for precision measurements has only become possible with our ability to produce atomic samples exhibiting temperatures of only a few millionths of a degree above absolute zero. Since the initial experiments a few decades ago, the field of atom optics has developed in many ways, with both fundamental and applied significance. The exquisite control of matter waves offers the prospect of a new generation of force sensors exhibiting unprecedented sensitivity and accuracy, for applications from navigation and geophysics to tests of general relativity. Thanks to the latest developments in this field, the first commercial products using this quantum technology are now available. In the future, our ability to create large coherent ensembles of atoms will allow us an even more precise control of the matter-wave and the ability to create highly entangled states for non-classical atom interferometry.
Inertial sensors based on cold atoms and light-pulse interferometry exhibit state-of-the-art sensitivity and ultra-low measurement bias that could revolutionize a variety of fields including geophysics and seismology, gravitational wave detection and fundamental tests of gravity, and inertial navigation. In the latter case, cold-atom interferometers are widely considered as breakthrough technology for future autonomous INSs. Nowadays, absolute quantum inertial sensors are available as commercial and field-deployable devices. Yet, their current size and complexity has not yet reached a technology readiness level compatible with mobile applications or plug-and-play operation by non-specialists. These systems are in desperate need of further development and miniaturization. We will present progress beyond these first experiments while exploring new methods relying on 3D matter-wave manipulation that can lead to interferometer geometries that are simultaneously sensitive to accelerations and rotations in 3D and can discern their vector components within a single measurement. These novel innovations produce additional sensitivity to rotations and gravity gradients which has not yet been exploited experimentally and could be a game changing innovation for future atomic sensors. The ability to measure the full acceleration and rotation vectors with a compact, high-precision, low-bias inertial sensor could strongly impact the fields of inertial navigation, gravity gradiometry, and gyroscopy.
We propose new multidimensional atom optics that can create coherent superpositions of atomic wave packets along three spatial directions. These tools can be used to generate light-pulse atom interferometers that are simultaneously sensitive to the three components of acceleration and rotation, and we discuss how to isolate these inertial components in a single experimental shot. We also present a new type of atomic gyroscope that is insensitive to parasitic accelerations and initial velocities. The ability to measure the full acceleration and rotation vectors with a compact, high-precision, low-bias inertial sensor could strongly impact the fields of inertial navigation, gravity gradiometry, and gyroscopy.
This dissertation reports on advancements in the construction of a quantum sensor for gravimetry based on matter interferometry. Ultra-cold strontium atoms (in the order of 1 μK) within a ring cavity in the bad cavity regime constitute the experimental setup and two distinct approaches were adopted for the comprehension of the systems operation. The first involved simulations of Ramsey-Bordé pulse sequence, specifically the π/2-π-π/2-spin echo sequence using the 689 nm transition of strontium. The sequence is commonly employed in matter interferometers and the simulations provided insights for future measurements. The expected precision of our system is within Δg/g < 10-8, showcasing its potential accuracy. The second approach focused on monitoring Bloch oscillations resulting from the interaction between atoms and cavity light, which induces a frequency proportional to the external force, in our case, gravity. Efforts were made during the experiment towards confirming the systems regime, leading to a significant observation of nonlinear Normal-mode splitting due to high saturation in the strong coupling regime, exhibiting a bi-stable behaviour.