[Keio Spintronics Network - Fujisawa Laboratory, Tokyo Institute of Technology]
The Fujisawa Group at Tokyo Institute of Technology is working to find out how precisely the behavior of single electrons can be controlled and measured. To do this, the researchers fabricate semiconductor nanostructures, and investigate their behavior on timescales at or below the nanosecond level. In this way, they study the particle and wave properties of electrons, as well as their interaction.
Q."In our research, we look not only at steady states of a single electron, but how the electron behaves dynamically; that is, "single-electron dynamics." In particular, by using nanostructures, we can control the dynamics very precisely and measure it very accurately. And in our research, we see what sort of applications can be envisaged by investigating electron properties in such nanostructures."
Electrons behaving dynamically can have various states -- not only groud states, but also excited states or superposition states. On the other hand, in today's electronics, the minimum current detectable is one femtoampere; that is, 10,000 electrons per second. So the Fujisawa Group is developing a device called a "single-electron ammeter." The researchers utilize semiconductor nanostructures to integrate quantum dots and a semiconductor point-contact charge detector in one device. This has enabled the Group to detect the flow of single electrons -- an achievement that wasn't possible until now.
Q."If you use quantum dots, you can detect whether a single electron is present or not. This is the principle of a single-electron ammeter, and we've succeeded, for the first time, in detecting the flow of single electrons in real time, including whether they flow to the right or left. Because we can detect the flow of even single electrons, we think this could be utilized in, for example, devices with low power consumption."
Not only are the researchers looking at electronics states with two values - whether a single electron is present or not, or whether its spin is up or down -- they're also investigating the quantum information of electrons. By studying quantum dynamics of one or two quantum bits, one can design a device for selectively performing various quantum operations.
Q."We use the very low temperature of 10 milli-kelvins to minimize noise, and under these conditions, we apply voltage pulses. For example, when we apply a pulse to a single-electron state located here, the electron can move back and forth between the two locations, and oscillate. By measuring such oscillatory phenomena, we can confirm the electron dynamics and the creation of quantum bits."
Currently, we're investigating whether we can utilize the quantum manipulation of single electrons to control and measure quantum mechanical states of two or three electrons. This kind of quantum manipulation is the most important technology needed for quantum computers.
Q."We've quickly come to understand cooperative motions, in which two electrons oscillate with opposite phases at a certain condition, or with the same phase at another condition. By using high-speed voltage pulse techniques, or using microwaves, it will be possible to control such electron dynamics precisely. And by fabricating nanostructures like this, it becomes possible to control quantum phenomena artificially. I think that's the most exciting thing about this research. "
Негізгі бет Ғылым және технология The ultimate in single-electron electronics
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