Print this page 14 September 2010 2010/28

Researchers protect the quantum state of a single electron spin

Scientists from Delft University of Technology (the Netherlands) and Ames Lab (USA) have succeeded to fully protect the spin state of a single electron from its environment. Single solid state spins are promising building blocks for new quantum technologies like a quantum computer, but uncontrolled interactions of the spins with their environment have been a major hurdle. By flipping the spin of a single electron with very short pulses the researchers have succeeded to mitigate these effects, effectively rendering the spin decoupled from its environment. Furthermore, they prove that the technique works for any possible spin state, a stringent requirement for use in a future quantum computer. Their results have been published online in the prestigious journal Science.

Quantum particles like atoms and electrons can be in multiple states at the same time. For example, the tiny magnetic moment of an electron, called 'spin', can point in two different directions simultaneously. If the spin of an electron is used as a bit in a quantum computer, it can be in the state 0 and 1 at the same time, while in a normal computer a bit is either 0 or 1. This will enable superfast computations. Building a quantum computer is challenging because the environment, which also consists of quantum particles – strongly influences the state of the spin.

The researchers work on single electrons in diamond, a material that has recently become very popular with quantum scientists. Unique to diamond is that quantum mechanical properties manifest themselves even at room temperature. This offers a great advantage for future applications. Previously, the researchers succeeded in measuring the spin state of a single electron in diamond and probing its environment. By using high-frequency pulses of only a few nanoseconds the team has now achieved control over the state of a single spin with a record-high accuracy. They have then exploited this control to protect the spin from its environment, a groundbreaking result.

The researchers periodically rotated the spin with very high precision so that the effects of the environment completely averaged out. This made it seem as though the spin was completely decoupled from its environment. The more often they flipped the spin, the longer its quantum state was preserved. With 130 pulses the state was already protected 25 times longer than previously measured. In addition, they proved that the protection works for any arbitrary spin state. These results are a true breakthrough for quantum science and engineering, where uncontrolled interaction with the environment have thus far proved to be the major bottleneck for new fundamental experiments and for applications.

The experiments have been performed at the Kavli Institute of Nanoscience at Delft University of Technology under supervision of Ronald Hanson (FOM-project leader). The work has received theoretical support from colleagues in Ames Laboratory of the US Department of Energy in the United States. First author Gijs de Lange is employed as a PhD-student by NWO. The research was financially supported by FOM, NWO, US DOE and DARPA. Ronald Hanson, a member of the Young Academy of the KNAW, received an NWO-Vidi grant for research on quantum information with diamond.

Reference
'Universal Dynamical Decoupling of a Single Solid-State Spin from a Spin Bath', G. de Lange, Z.H. Wang, D. Ristè, V.V. Dobrovitski, and R. Hanson, Science (DOI: 10.1126/science.1192739), online publised on 9 September 2010.
http://www.sciencemag.org/cgi/content/abstract/science.1192739v1

Information
Ronald Hanson, Kavli Institute of Nanoscience, Delft University of Technology, phone (015) 278 71 88.
For more information, please visit: http://www.tnw.tudelft.nl/live/pagina.jsp?id=1facd289-2d36-423c-a595-b6f78063b316&lang=en

Contact:

Melissa Vianen

Figure 1. Overview of the sample

Overview of the sample obtained by scanning a laser across the sample and detecting the emitted light. The gold areas are sections of the electronic circuit used for the fast pulses. The gold structures are patterned directly on a 4x4x0.5 millimeter diamond sample using nanolithography. A section of the diamond in between the gold structures is visible; the white dots are single electron spins. Orange circles (NV1 and NV2) show which spins were used in the experiments. The zoom-in shows a schematic overview of the diamond at the nanoscale. In the experiments a single spin (orange) is decoupled from an environment of surrounding spins (green).
Figure 2. Protecting the quantum state of a single spin

Quantum state decay curves for an increasing number of pulses (N). The value on the y-axis quantifies in how far the measured state after a certain waiting period corresponds to the initial state. A value of 1 implies that the measured state is identical to the initial state, as desired. The higher the number of pulses, the longer it takes before the spin state decays.