Physicists Don't Flip Spin but Find Possible Electron Switch

University of Oregon researchers trying to flip the spin of electrons with laser bursts lasting picoseconds (a trillionth of a second) instead found a way to manipulate and control the spin -- knowledge that may prove useful in a variety of new materials and technologies.

Physicists in recent years have been pursuing a variety of routes to tap electron spins for their potential use in quantum computers that can perform millions of computations at a time and store immense quantities of data or for use in emerging optic devices or spintronics.

"Spin is another dimension of electrons," said Hailin Wang, a professor of physics at the UO. "The electronics industry has depended on electron charges for more than 50 years. To make major improvements, we now need to go beyond charges to spin, which has been very important in physics but not used very often in applications."

Wang and his doctoral student Shannon O'Leary theorized that they could flip an electron's spin up to down, or vice versa, by using a nonlinear optical technique called transient differential transmission. They describe their "failure" to flip the spin and their unexpected discovery in Physical Review B.

The overall goal, Wang and O'Leary said, is to be able to force the spin to flip using light. Their studies involved the use of nonlinear optical processes of electron spin coherence in a modulation-doped CdTe quantum well -- semiconductor material formed from cadmium and tellurium, sandwiched in a crystalline compound between two other semiconductor barrier layers. A doped quantum well contains extra embedded electrons in a near two-dimensional state.

O'Leary initialized a spin in an experiment using a "gyro-like" arrangement with a short pulse of laser. At specific times, she hit the spin with another laser pulse with the absorption energy of an exciton (an electron-hole pair) or trion (a charged exciton). Hitting the spin with a third pulse allows them to study what impact the second pulse had on the spin.

"We know that in this particular system, excitons quickly convert into trions by binding to a free electron," O'Leary said. "One surprising aspect is that injecting trions directly does not manipulate the spin. So the manipulation effect has to do with the conversion of the excitons to trions."

The behaviors they discovered were unexpected but intriguing, Wang said. "We were not able to flip the spin, but what we found is something quite puzzling, quite unexpected, that was not supposed to happen. We now want to understand why the system works this way. This will require some more work. We wanted to get from point A to B, but we went to C."

The detour, however, "shows that we can manipulate the spin when we inject excitons at appropriate times in the precession cycle of the spin," O'Leary said. "The result gives scientists a new tool for manipulating spins, and it may prove to be a handy method because it simply requires shining a pulse of light of the appropriate energy at the right time."

Source: University of Oregon

Related stories:

Toward Plastic Spin Transistors
(PhysOrg.com) -- University of Utah physicists successfully controlled an electrical current using the "spin" within electrons – a step toward building an organic "spin transistor": a plastic semiconductor switch for future ultrafast computers and electronics.
Billion-dollar European probe set for asteroid encounter
Far from Earth, a robot spacecraft has been prodded from deep slumber to make a rare encounter with an asteroid, the intriguing orbital debris that could offer clues into the making of the Solar System.
Fast quantum computer building block created
(PhysOrg.com) -- The fastest quantum computer bit that exploits the main advantage of the qubit over the conventional bit has been demonstrated by researchers at University of Michigan, U.S. Naval Research Laboratory and the University of California at San Diego.
New Speed Record for Magnetic Memories
(PhysOrg.com) -- An experiment carried out at the Physikalisch-Technische Bundesanstalt (PTB) has realized spin torque switching of a nanomagnet as fast as the fundamental speed limit allows. Using this so-called ballistic switching future non-volatile magnetic memories could operate as fast as the fastest non-volatile memories. The experiments are described in the next issue of Physical Review Letters (22 August, 2008).
Quantum Chaos Unveiled?
(PhysOrg.com) -- A University of Utah study is shedding light on an important, unsolved physics problem: the relationship between chaos theory - which is based on 300-year-old Newtonian physics - and the modern theory of quantum mechanics.
Warming up for Magnetic Resonance Imaging
Standard magnetic resonance imaging, MRI, is a superb diagnostic tool but one that suffers from low sensitivity, requiring patients to remain motionless for long periods of time inside noisy, claustrophobic machines. A promising new MRI method, much faster, more selective — able to distinguish even among specific target molecules — and many thousands of times more sensitive, has now been developed in the laboratory by researchers at the Department of Energy's Lawrence Berkeley National Laboratory and the University of California at Berkeley.
NIST 'Quantum Logic Clock' Rivals Mercury Ion as World's Most Accurate Clock
An atomic clock that uses an aluminum atom to apply the logic of computers to the peculiarities of the quantum world now rivals the world's most accurate clock, based on a single mercury atom. Both clocks are at least 10 times more accurate than the current U.S. time standard.
Analogue logic for quantum computing
Digital logic, or bits, is the only paradigm for the IT world, and up to now researchers used it almost exclusively to study quantum information processing. But European scientists, in a series of firsts, have proved that an analogue approach is far easier in the quantum world.

News discussion:

Physics news