Nanodiamond levitated in free space with lasers could further quantum computing
August 16, 2013
A recent experiment by researchers at the University of Rochester has managed to suspend a nano-sized diamond in free space with a laser and measure light emitted from it. Like the scientists who recently managed to freeze light in a crystal for up to a minute, these scholars believe their work has applications in the field of quantum computing.
To conduct the experiment, the researchers sprayed an aerosol containing dissolved nanodiamonds into a chamber. A laser was focused inside the 10-inch (25.4-cm) diameter vacuum container, to which, once sprayed, the diamonds are attracted. Trapping particles with lasers isn't new, but this is the first time levitation has been achieved with nanodiamonds, which are diamonds that measure as little as 100 nanometers (one-thousandth the diameter of a human hair). This technique is known as laser trapping and has the potential to push particles toward their quantum ground state.
Once the tiny gem was levitating in free space, the researchers used another laser to make defects within the diamond emit light at given frequencies. According to the researchers, this photoluminescence process has the potential to excite the system and cause what is known as Bohr spin quantum jumps, which are changes in spin configuration of the internal defect.
The process of photoluminescence, or light emission after the absorption of photons, is due to the defects in the tiny diamond. When the system is excited, it changes the spin (a type of angular momentum carried by the basic building blocks of particles), and when the it relaxes, after the change, other photons are emitted. This occurs because nitrogen atoms replace some of the carbon atoms in the diamond. Once the nitrogen is nested in the diamond's atomic structure, it is possible to excite electrons with a laser.
This provides the potential to turn the nanodiamond into an optomechanical resonator. According to Nick Vamivakas, an assistant professor of optics at the University of Rochester, these are structures in which the vibrations of the system can be controlled by light. "We can start considering systems that could have applications in the field of quantum information and computing," he says.
Optomechanical resonators have the potential to be used as incredibly precise sensors, which could lead to uses in microchips. This concept would also provide insight into friction at the nanoscale, giving us a better idea of how friction affects things on the macroscale.
Beyond friction, these resonator systems have the potential to create Schrödinger Cat states, which Vamivakas tells Gizmag, "are quantum states of macroscopic objects – not microscopic things like single electrons or single photons, but large objects like cats." Typically, quantum effects are reserved for microscopic objects.
Schrödinger's Cat is a thought experiment that presents a cat that may be both dead and alive, depending on an earlier random event. Typically this event refers to a cat in a box that may or may not have been poisoned, so until the box is opened to discover a dead or living cat, it is in a quantum state – or both living and dead.
"Cat or cat-like states contradict our everyday experiences since we do not see common things in quantum states," Vamivakas explains. "The question is: where is this boundary between microscopic and macroscopic? By generating quantum states of larger and larger objects, we can hone in on a boundary ... if there is one." With the levitating crystal, the team still needs to cool the crystal better, which they are hoping can be achieved with a few technical improvements.
Though parts of the process of trapping nanodiamonds could be seen as somewhat rudimentary – spraying and hoping to trap a diamond – the researchers are already looking toward making more experiments happen.
D-Wave has claimed to have already constructed a made commercially available a quantum computer, but there is still some disagreement in scientific circles on whether that is the case.
When Gizmag asked Vamivakas about how far he thought we were from reliable quantum computing, he said, "I don't really like to comment on how far or close quantum computing is. There is a lot of great progress being made in a variety of systems towards this goal. In fact recently there have been some remarkable achievements regarding quantum simulation - using one quantum system to simulate another – and the idea of quantum simulation crystallized around the same time as a quantum computer."
A paper by the researchers regarding their nanodiamond levitation was published in Optics Letters.
The video below provides a brief overview of the nanodiamond levitation experiment.
Source: University of Rochester