Bloch Floquet Bands Enable Portable Gravity Sensors
Bloch-Floquet engineering
Scientists developed a breakthrough matter-wave interferometry method that traps quantum gasses in an optical lattice for high-precision measurements. The team synthesized energy band structures that act as mirrors and splitters using Floquet engineering to develop a compact, flexible force sensor. This research advances with the finding of “magic” band topologies that are insensitive to lattice intensity noise. This invention tackles a major technological challenge by protecting the interferometric phase from systematic mistakes in traditional traps. In conclusion, this programmable platform provides a dependable and portable quantum metrology system for basic physics research and gravitational sensing.
Quantum Leap in Sensing: “Magic” Band Structures Allow Compact Gravity Detectors
A novel, noise-tolerant method for sensing forces using trapped atoms developed by UCSB researchers could reduce the size of massive gravity-detecting devices to a tabletop. Using “magic” Floquet-Bloch band structures, the researchers created a quantum sensor that is resistant to trap noise that plagues small devices.
Free-Fall Issue
For years, matter-wave interferometry has been the best force sensing method. These experiments use “free-fall” mechanisms to launch or drop atoms enormous distances. Scientists have built 100-meter drop towers and flown experiments into low Earth orbit to extend atom flight and increase sensitivity.
Though strong, these arrangements are immobile. Researchers in Nature Communications reported that continuously-trapped interferometers can cover huge spacetime areas without requiring long freefall time or high experimental size. However, "dephasing," induced by instabilities in the trapping potential, or laser beam disruptions, makes it difficult to trap atoms and ruins precision quantum measurements.
Making the “Magic” Fix
Under Professor David M. Weld, the UCSB team applied Floquet engineering to avoid this. By periodically generating an amplitude-modulated optical lattice, this approach creates novel energy landscapes for atoms.
The group found “magic” band structures. These were inspired by the “magic wavelengths” of the most precise optical lattice clocks. These magic bands have first-order interferometric phase insensitivity to lattice intensity noise. Despite laser trap flickering, atoms continue measuring.
How the Quantum Loop Works
Starting the experiment, the Bose-Einstein condensate (BEC) had 200,000 lithium-7 atoms. To avoid atom collisions and measurement failure, the team uses a Feshbach resonance to zero out atom interactions.
Atoms are placed in a horizontal optical lattice when ready. Using a magnetic field gradient to tug on the atoms starts Bloch oscillations, a quantum phenomena in which the atoms “bounce” across the lattice structure.
Several “quantum gates” power the interferometer:
Landau-Zener Beamsplitters: Instead of mirrors, researchers use “avoided crossings” in the intended energy bands to split the atomic wavepacket into two channels.
Stückelberg Evolution: The two paths accrue a relative phase depending on the external force.
The final population of atoms in various energy bands reveals the force's intensity when the paths reunite at a second beam splitter.
Programmable Quantum Toolbox
Programmability is one of this technique's most exciting properties. Since radio-frequency (RF) modulation of lasers creates “loops” for atoms, researchers may “draw” practically any path for them.
Building interferometers with larger loop areas allowed them to alter the sensor's sensitivity on the fly. They also showed that pulsed beam splitters might prevent “leaks” into undesirable energy states, enabling bigger loops that could span numerous Brillouin zones.
Looking for “New Physics”
Even though the current experiment used a horizontal lattice without gravity, the method is perfect for weak force detection.
These small, durable sensors can be used for “fifth force” searches or micron-scale gravity deviations, according to the experts. Evaluation of non-Standard Model physics ideas requires these observations.
The researchers believe Floquet engineering's adaptability and strength may permit more complex sequences in the future, possibly with machine learning to maximize sensitivity. The restricted and “magic” atoms allow the UCSB team to develop “tunable, compact, simple, and robust” quantum sensors.
