New Haven, Conn. -- Yale physicists have created a "squeezed state" of atoms using Bose-Einstein condensate (BEC), a sample of rubidium atoms so cold that all of the atoms collapse into a single quantum state.
The results of their study, published in a recent issue of Science, may lead to improvements in the field of precision measurement and could improve navigational systems on planes and ships.
"Our experiments are the first to observe number-squeezed states in a sample of atoms," said Chad Orzel, postdoctoral associate in physics at Yale and first author on the study. "Combining the number-squeezed states that we make with the techniques used in atom interferometry, we hope to dramatically improve the sensitivity of detectors for rotation and acceleration, and gradients in gravity. Accelerometers and gyroscopes (rotation detectors) are currently used in navigation systems for planes and ships, and gravity gradiometers have applications in submarine navigation, and in locating ore deposits for mining."
Mark Kasevich, a collaborator on the study, said creating a squeezed state of atoms is like playing a game of modified ice hockey, using a special puck and a very narrow goal. "The object of the game is to get the puck into the goal, but in this modified game, the puck diameter is initially wider than the width of the goal, making it nearly impossible to score a goal," Kasevich said. "But if the puck is made of a deformable material, it could be squeezed into a long, thin, cigar-like shape. Although the puck's length greatly exceeds its width, if the puck is shot head-on into the goal, it could now go through. At this point we don't care that the puck is elongated, so long as its width is narrower than the width of the goal, we can score."
Kasevich said many quantum-mechanical precision measurements are similar to this. "Often we can trade-off a parameter we care about in one dimension, such as the number of atoms or the width of the puck, for something we don't care about in another dimension, such as the phase of the field or the length of the puck, to enable an outcome which would have not been possible with the non-squeezed state."
The "squeezing" is a metaphor that describes a way of working around the limits of the Heisenberg Uncertainty Principle, which places a limit on how accurately the value of two complementary physical quantities can be measured. The Uncertainty Principle states that it is impossible to know both the exact position and the velocity of a particle. "If we make a better measurement of the position, we lose our knowledge of how fast the particle is moving, and vice versa," said Orzel.
The Uncertainty Principle also states that there is a similar relationship between the number of particles in a given state and a quantum-mechanical property of those particles referred to as the "phase" of that state. "If we make a very precise measurement of the number of particles we have, we lose all information about the associated phase," said Orzel. "In typical real-world situations, both the phase and the number are known reasonably well, but are slightly uncertain."
Orzel and collaborators loaded a Bose-Einstein Condensate into an array of atom traps created by a single laser beam. By manipulating the intensity of the trapping laser and the strength of the interactions between the atoms, they were able to reduce the quantum uncertainty in the number of atoms in a single well from +/- 50 atoms to +/- 2 atoms.
"Quantum states of this type, with reduced uncertainty in the number of particles and increased uncertainty in the phase, are called 'squeezed states,' and have been studied extensively in light," said Orzel. "This is the first time anyone has seen number-squeezing in atoms."
The number-squeezed states produced in the laboratory have the potential to dramatically improve the sensitivity of detectors based on atom interferometry. Atom-interferometric detectors for rotation, acceleration and gravity gradients are already as good as state-of-the art detectors based on more traditional means.
"The use of squeezed states in atom interferometry could improve the sensitivity by an order of magnitude or more," Kasevich said.
In addition to Orzel and Kasevich, other researchers on the study at Yale included Ari Tuchman, Mathew Fenselau, and Masami Yasuda, who is now at Tokyo University.
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