Illustration of NIST's Quantum Crystal. Credit: Burrows/JILAThe National Institute of Standards and Technology (NIST), physicists, have "entangled" the mechanical motion and electronic properties of tiny blue crystals. This gives it a quantum edge when measuring electric fields with record-setting sensitivity. This may help to improve understanding of the universe.150 beryllium-ions (electrically charged particles) are contained in a magnetic field. They self-arrange to form a flat 2D crystal measuring 200 millionthsof a meter in size. These quantum sensors can detect signals from dark matter, a mysterious substance which could be subatomic particles or interact with normal matter via weak electromagnetic fields. Dark matter can cause crystals to move in unusual ways. This is revealed by collective changes in the crystal's electron properties known as spin.Researchers can measure the vibrational excitation in the crystal, as described in Science's Aug. 6 issue. This flat plane moves up and down just like a drumby by monitoring changes in the collective spinning. The measurement of spin is referred to displacement.The sensor measures external electric fields with the same frequency as crystals, and has a sensitivity that exceeds 10 times that of any atomic sensor. The sensor can measure 240 nanovolts per second. Researchers use a weak electric field in experiments to stimulate and test the crystal sensor. Such a signal would be the basis of a dark matter search.John Bollinger (left), and Matt Affolter (right) adjust the laser array and optics array that were used to trap and probe the berylliumions in the large magnetic room (white pillar, left). The ion crystal may help detect mysterious dark matter. Credit: Jacobson/NISTJohn Bollinger, NIST senior author, stated that ions crystals could detect some types of dark matter. These include hidden photons and axionsthat interact with normal material through a weak electrical field. "The background signal that dark matter creates depends on its mass and oscillates at a frequency that is dependent on the mass of the dark material particle. This type of dark matter has been searched for for over a decade using superconducting circuits. The motion of trappedions gives rise to sensitivity at a variety of frequencies.Bollinger's group has been working on the ion crystal more than a decade. The researchers have developed a new laser light that can be used to capture the collective motion and spins from large numbers of ions. They also use what they call a "time reverse" strategy to detect the results.Ana Maria Rey, an NIST scientist, collaborated on the experiment. She works at JILA (a joint institute of NIST & the University of Colorado Boulder). Bollinger stated that the theory work was crucial in understanding the limitations of the laboratory setup. It provided a new model to understand the experiment that works for large numbers trapped ions.Rey observed that entanglement can cancel the ions' intrinsic quantum noise. However, it is hard to measure the entangled state without destroying information shared between spins and motion.Rey stated that John can reverse the dynamics to disentangle spin and motion after displacement has been applied. This time reversal separates the spin from the motion. The collective spin now has the displacement information stored on its spin. We can measure the spins to determine the displacement. This is very neat!To produce the desired spin values, researchers used microwaves. The ions can be spun up (often visualized as an arrow pointing upward), or spin down, depending on their quantum state. The ions had the same spin, first spinning up, then moving horizontally. When excited, they then rotated in a manner that is typical of spinning tops.To entangle the collective spin and the motion, cross-laser beams with a frequency almost equal to the motion were used. The crystal was vibrally excited. To undo the entanglement, the same microwaves and lasers were used. Researchers measured the spin level of fluorescence ions to determine the crystal's movement (spin up scatters light, while spin down is dark).The future is likely to see a thirtyfold increase in the ability to sense by increasing the number to 100,000 ions through the creation of 3D crystals. The stability of the crystal's excited movement might also be improved. This would increase the time reversal and precision of the results.Rey stated that if we can improve this aspect, the experiment could become a fundamental resource to detect dark matter. We know that 85% of all matter in the universe is dark matter. However, we don't know what dark matter is. This experiment could help us uncover this mystery in the future.Researchers from the University of Oklahoma were co-authors.Continue reading Improving the constraint in the lab for exotic spin interactionK.A. Gilmore, M. Affolter R.J. Lewis Swan, D. Barberena E. Jordan, A.M. Rey, and J.J. Bollinger. Quantum-enhanced sense of displacements, electric fields and two-dimensional trapped ion crystals. Science. August 5, 2021. Science K.A. Journal information Gilmore, M. Affolter R.J. Lewis Swan, D. Barberena E. Jordan, A.M. Rey, and J.J. Bollinger. Quantum-enhanced sening of displacements, electric fields and two-dimensional trapped ion crystals.. Aug. 5, 2021. DOI: 10.1126/science.abi5226
