# Physics – Towards flawless atomic optics

Physics 15, 162

Engineering so-called Flockett states leads to near-perfect atomic-optics elements for matter-wave interferometers—which could enhance the ability of these devices to explore new physics.

Since Michelson and Morley’s famous “luminous aether” experiment, optical interferometry has provided valuable tools for studying fundamental physics. At present, sophisticated applications of this technology include its use as a high-resolution ruler to detect gravitational waves (see Focus: The Moon as a Gravitational Wave Detector) and as a quantum computing platform (see Perspective: a quantum leap ahead of quantum primacy). But as methods for cooling and controlling atoms have advanced, a new type of interferometer has become available, in which light waves are replaced by matter waves. [1]. Such devices can measure inertial forces with greater sensitivity than those of optical interferometers [2] And it could reveal new physics beyond the Standard Model. In a new experiment, Jason Hogan and colleagues at Stanford University address one of the obstacles that has limited the capabilities of matter wave interferometers so far: the inefficient coupling between the atoms that make up matter waves and the light pulses used to manipulate them. [3]. Their technique could lead to matter-wave interferometers sensitive enough to detect fluctuations in the Earth’s rotation rate or manifestations of general relativistic effects such as the ‘skew’ of spacetime predicted by some alternative gravitational theories.

Whether the interferometer uses light waves or matter, its sensitivity to inertial effects such as rotation depends on the separation between the arms of the interferometer. In matter wave interferometers, large arm separation requires the creation of coherent superpositions of atomic momentum states so that the atomic wave function can be separated over large distances—usually a few centimeters. Large arm separation results in strong interferometer sensitivity at the cost of lower interferometer variance—that is, the signal-to-noise ratio. To maintain a high contrast with large arm breaks, two methods are generally used. In both methods, light pulses are used as atomic optical elements to deflect atomic trajectories by transmitting the moment of the photon to the atoms. The first method obtains the desired contrast of the interferometer by increasing the size of the instrument—as is the case, for example, in the modern cold-fountain atom gyroscope used to measure the Sagnac effect with a resolution of 25 ppm. [4]. The second method does this by maximizing the momentum transmitted by light pulses to the atoms [5].

Researchers using the latter technique — called large momentum transfer (LMT) — face a problem: The atoms in each arm move at different speeds, producing a differential Doppler-shift interferometer beam deconvolution error. The resulting mismatched light coupling in the arms results in a loss of contrast. To mitigate this problem, conventional LMT atom optics use short, wide-band pulses to deflect the atoms. In this approach, the broad bandwidth of the pulses can accommodate a range of deconvolution errors but results in a loss of efficiency and variance. Hogan and colleagues propose a different approach in which pulses are also used to control atom states in a way that automatically corrects the intrinsic deconvolution error. They showed that frequency detonation of interference beams can be compensated for by modulating the interaction of the atom with light.

Specifically, the team demonstrates a matter-wave interferometer in which strontium atoms oscillate between 1s0 And the 3s1 States. By modifying the inter-atomic coupling amplitude and interference beams in 1s03s1 Optical transition, the researchers generate a set of Flockett states on which the initial atomic momentum state is projected. Atoms undergo a change in their internal state while simultaneously changing their external state – increasing or decreasing their torque. This process can be achieved with close to 100% accuracy. How is this performance possible? We can look at this process from two perspectives.

From an energy point of view, one might say, for a given Doppler detonation of an interferometer beam, the modulation creates a sideband at the frequency required to compensate for this detonation. The mod adds the lost power needed to achieve the resonant state. In other words, coupling modulation broadens the light beam spectrally over a frequency band that covers the Doppler separation.

From the point of view of the quantum state, by modulating the coupling of the atom to light, the authors create multiple sets of time-dependent wear states that are characterized by a well-defined number of modulation energy quantums. Then, by adjusting the coupling temporal profile, they can make the atom light system evolve from one manifold to another (Fig. 1). Since these manifolds, or sub-flucket spaces, correspond to different momentum or propagation velocities of the atoms, one can efficiently transmit a large amount of photon torque to the atoms without losing the interferometer anisotropy. This is the working principle of Flocket Atom optics.

As a result of this process, Hogan and colleagues achieved a large momentum transfer of 400 ħk—Set state-of-the-art LMT interferometers — but with a higher profile

$\sim$

10% marginal visibility and 99.4% effective count reflection for interferometer cases. Thus, the proven Flockett atom optics provide optimum quasi-coherent case handling. Compared with other techniques currently in use, this new method allows for a robust, flexible and easy-to-implement solution (only three parameters are needed) for error-correction decoding in large material wave interferometers. In addition, engineering atom-light coupling in this way may offer new perspectives, for example, controlling the transfer of momentum to atoms even when they are trapped in a modified potential. [6]Geometric decoherence-free subspaces for quantum information processing [7]the performance of quantum simulation [8].

## references

1. Chapter J. Purdy, “Atomic Interferometry with Internal State Labeling,” Phys. Lett. a 14010 (1989).
2. Peters et al.“High-Resolution Gravimetric Measurements Using Atomic Interferometry,” metrology 3825 (2001).
3. T Wilkason et al.“Atomic interferometry using fluorocoiter optics,” Phys. Reverend Litt. 129183202 (2022).
4. R. Gautier et al.“Accurate measurement of the Sagnac effect for matter waves,” Sciences. case. 8 (2022).
5. GM McGurk et al.“Large-area optical pulse atom interferometry,” Phys. Reverend Litt. 854498 (2000).
6. a. Bushol et al.“Limitations of the Modulation Method for Smoothing the Roughness of Wire Routing,” Phys. Reverend A 77023624 (2008).
7. chen et al.Flucite control of quantum dissipation in spin chains. Phys. Reverend A 91052122 (2015).
8. n. Goldman et al.“Ultra-cold Topological Quantum Material in Optical Synapses,” nat. Phys. 12639 (2016).

## About the author

Carlos L. Jarrido Alzar is an Associate Research Professor in Time-Space Reference Systems (SYRTE) at the Paris Observatory. He received his Ph.D. He received his Ph.D. in quantum optics at the University of São Paulo’s Institute of Physics in 2002. He then held the position of Assistant Professor at the Danish National Research Foundation’s Center for Quantum Optics until 2005 at the Niels Bohr Institute in Copenhagen. After a postdoctoral stay at the Graduate Institute of Optometry in France, he transferred to SYRTE. There, his current research focuses on developing atomic-guided interferometry on corn chips for compact inertial navigation applications.

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## Subject areas

optics atomic and molecular physics

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