Nanotechnology Breakthrough: Single-Spin Transistors?
The joke goes:
Q: “Why is a mouse when it spins?”
A: Because the higher, the fewer.
But this is no joke:
Q: “Why is an electron when it spins?”
A: Because it may also allow development of single-spin transistors for coherent spintronics, and solid-state devices for quantum information processing.
On September 9, 2010, Experimentalists from Delft University of Technology’s Kavli Institute of Nanosciences — in collaboration with theorists at the U.S. Department of Energy’s Ames Laboratory — announced a breakthrough in the area of controlling single quantum spins. The announcement was published in Science Express.
[Here’s the accessible summary, “Physicists Cross Hurdle in Quantum Manipulation of Matter,” Here’s the original pdf]
G. De Lange of Kavli Institute and his collaborators demonstrated a type of quantum control over a single quantum magnetic moment (spin) of an atomic-sized impurity (nitrogen-vacancy, or N-V center) in diamond, which, in the impure form, has atypical magnetic and optical properties. The delicate quantum states induced by the experimenters are usually easily destroyed by the tiniest interactions with the outside world, not exactly the stable and robust properties desired for commercial devices..
Zapping the impure diamond with high-precision and cunningly designed sequences of electromagnetic pulses, researchers could protect the arbitrary quantum state of a single spin. Next, they made the spin evolve as if it was completely decoupled from the outside world. By using these techniques to reach a 25-fold increase in the lifetime of the quantum spin state at room temperature, the team has made the first demonstration of “universal dynamical decoupling” realized on a single solid state quantum spin.
Associate Professor Ronald Hanson, the leader of Dutch experimental group from the Delft campus of the Kavli Institute of Nanoscience: “Uncontrolled interactions of the spins with the environment have been the major hurdle for implementing quantum technologies. Our results demonstrate that this hurdle can be overcome by advanced control of the spin itself.”
Where does this research go next? The team is careful not to engage in hype. Rather, they emphasize its value in extending the theoretical understanding of quantum mechanics. This, in turn, can lead to the use of N-V centers in diamond to create extremely sensitive nanoscale magnetic sensors, and eventually, to implement qubits for larger-scale quantum information processing.
Viatcheslav Dobrovitski, who led the theoretical research team at the Ames Laboratory: “Implementing dynamical decoupling on a single quantum spin in solid state at room temperature has been an appealing but distant goal for quite a while. In the meantime, much theoretical and experimental knowledge has been accumulated in the community. We used this knowledge to design our pulse sequences, and the collaboration between theory and experiment greatly helped us in this work.”
Let’s put this in context. It’s been 3 years since Harvard University scientists announced [“Single Spinning Nuclei In Diamond Offer A Stable Quantum Computing Building Block,”] that individual carbon-13 atoms in a diamond lattice can be manipulated with extraordinary precision, thus creating a prototype stable quantum mechanical memory, and a quantum register (small quantum processor) operating at room temperature.
It’s been almost exactly a year since it was shown [Kaestner, 2009; “New Development in Spintronics: Spin-polarized Electrons On Demand, With A Single Electron Pump,” Science Daily, Sep 19 2009, that such a single electron pump can be reliably operated in high magnetic fields, delivering on demand exactly one single electron with predefined spin polarization per pumping cycle.
The gigahertz range cycle time, and robust technology suggests that spin-polarized single electron pumps might be a promising approach to future spintronic applications. Spintronics has been advertised [“The Spin On Spintronics,” Science Daily, 30 Aug 2006] as someday allowing personal computers that are both small and super-fast; boast gigabytes or terbaytes of memory; boot up instantly; have a standby mode that consumes no electric power and yet keeps programs and data instantly available in active memory. We’ll see, as the realities of R&D and the marketplace determine which of a dozen approaches is viable.