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(麻豆淫院Org.com) -- "Quantum computing could provide a way to significantly speed up the way we process certain algorithms," Malcolm Carroll tells 麻豆淫院Org.com. "The primary issue, though, is that you need a well controlled two-level system." He also points out that problems exist in terms of noise in quantum computing. One of the essentials in some models of quantum computing is utilizing the "spin" of certain electrons. Controlling the spins in GaAs quantum dots has advanced to a fairly sophisticated point, but there is still the issue of noise.

One way to reduce the noise in a quantum system is to use silicon. 鈥淪ilicon spins have long coherence times. The noise is reduced with silicon, and that is an advantage for this type of quantum computing, since you want to maintain coherence for as long as possible. However, it鈥檚 been a challenge to isolate and manipulate silicon spins,鈥� Carroll explains.

In order to find a way to isolate and control silicon spins, Carroll, a scientist at Sandia National Laboratories in Albuquerque, New Mexico, has been working with a team. One member of the team, Tzu-Ming Lu, has been helping with the idea of controlling the number of spins with a gate, rather than using doping methods. The work on this project is published in Applied 麻豆淫院ices Letters: 鈥淓nhancement-mode buried strained silicon channel quantum dot with tunable lateral geometry.鈥�

鈥淚ncreasing the distance between the spins and defects is part of the benefit of this process,鈥� Lu explains. 鈥淥ne of the ways to get spins is to use doping to provide electrons. However, the defects are closer. Instead, we use a gate in an alternative enhancement mode approach.鈥�

Lu鈥檚 alternative enhancement mode technique was demonstrated during his time as a graduate student at Princeton; it set a world record in mobility. However, the set up was too big to be used effectively for quantum computing. 鈥淲hat we鈥檝e done is taken the large scale field effect transistor structure, and make it into a few-electron quantum dot,鈥� Carroll says. 鈥淲e squeeze it down for better control of single electrons in this system.鈥�

The structure, rather than being a single quantum dot, is actually a double quantum dot. 鈥淭he dots are placed next to each other, and this gate structure makes it easier to control the spins in the device,鈥� Carroll explains.

But why the focus on silicon? Well, as Carroll mentions earlier, the coherence time is longer. There is less noise at low temperature when silicon is used. Caroll and Lu also point out that there is already a solid silicon infrastructure. 鈥淲e already have silicon foundries that can build the device,鈥� Lu says. 鈥淧eople are used to working with silicon, and so you have very clean environment for the electrons, further reducing unintended noise sources.鈥�

Now that some control over these silicon quantum dots has been demonstrated in a few-electron device, the team at Sandia is ready to move on to the next steps. 鈥淲e aren鈥檛 sure that our device is small enough yet,鈥� Carroll says. 鈥淎dditionally, there was an instability in this particular device. We鈥檝e worked through a new design, and we want to check to make sure that the stability issue is gone.鈥�

鈥淧rogress is being made in this area, and we鈥檙e not the only ones,鈥� Carroll continues. 鈥淪ilicon is a promising approach to quantum computing because of the long coherence times. This materials approach to isolating and controlling spins is very promising and it could allow even more people to realize the benefits of using silicon in quantum computing.鈥�

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