James K. Thompson, a fellow at the University of Colorado Boulder and the National Institute for Standards & Technology, and his team have successfully combined two of the “spookiest” aspects of quantum mechanics to create a better quantum sensor. These two features are entanglement between atoms and atom delocalisation.
When it comes to the unusual consequence of quantum mechanics, where what occurs to one atom somehow influences another atom somewhere else, Einstein first described entanglement as producing spooky activity at a distance.
Quantum simulators, quantum computers, and quantum sensors all depend on entanglement. The ability of a single atom to exist simultaneously in multiple locations is known as delocalisation, and it is another unsettling element of quantum physics.
The team has realised a matter-wave interferometer that can sense accelerations with a precision that surpasses the usual quantum limit (a restriction on the accuracy of an experimental measurement at a quantum level), combining the unsettling properties of both entanglement and delocalisation.
Future quantum sensors will be able to deliver more accurate navigation, examine for necessary natural resources, and determine essential constants like fine structure and gravitational constants more precisely, among others.
Two things must normally be brought very, very close to one another for them to interact. Even when they are millimetres or more apart, the Thompson group has figured out how to entangle thousands to millions of atoms.
To enable information to move between the atoms and knit them into an entangled state, they use light bouncing between mirrors, or what is known as an optical cavity. They have generated and seen some of the most densely entangled states ever generated in any system, be it atomic, photonic, or solid-state, using this special light-based technique.
The group developed two separate experimental procedures using this method, both of which they applied in their most recent work. In the first method, which is also known as a quantum non-demolition measurement, they pre-measure the quantum noise linked to their atoms and then simply take that measurement out of the equation.
The quantum noise of each atom becomes correlated with the quantum noise of all the other atoms by a process known as one-axis twisting in the second method, where light is introduced into the cavity. This makes it possible for the atoms to work together and get smoother.
The matter-wave interferometer is one of the most precise and reliable quantum sensors available today. The concept is to use laser light that has been both absorbed and not absorbed to induce atoms to move and not move at the same time. As a result, the atoms eventually find themselves simultaneously in two places.
In a quantum adaptation of Galileo’s gravity experiment, which involved dropping objects from the Leaning Tower of Pisa, the team was able to measure how far the atoms travelled along the vertically oriented cavity because of gravity, but with all the precision and accuracy that comes with quantum mechanics.
The team was then able to use the light-matter interactions to produce entanglement between the many atoms to make a quieter and more accurate measurement of the acceleration caused by gravity by learning how to operate a matter-wave interferometer inside of an optical cavity.
The team gains from using entanglement as a resource in quantum sensors and hopes that others will use this novel entangled interferometer approach to spur further developments in physics.
