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5 December 2013 11:26 am ,
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An animal rights group known as the Nonhuman Rights Project filed lawsuits in three New York courts this week in an...
Researchers have been hot on the trail of the elusive Denisovans, a type of ancient human known only by their DNA and...
Thousands of scientists in the Russian Academy of Sciences (RAS) are about to lose their jobs as a result of the...
Dyslexia, a learning disability that hinders reading, hasn't been associated with deficits in vision, hearing, or...
Exotic, elusive, and dangerous, snakes have fascinated humankind for millennia. They can be hard to find, yet their...
Researchers have sequenced and analyzed the first two snake genomes, which represent two evolutionary extremes. The...
Snake venoms are remarkably complex mixtures that can stun or kill prey within minutes. But more and more researchers...
At age 30, Dutch biologist Freek Vonk has built up a respectable career as a snake scientist. But in his home country,...
- 5 December 2013 11:26 am , Vol. 342 , #6163
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New Logic for Quantum Device
30 October 2003 (All day)
A quantum computer built from silicon-style circuits just crept closer to reality, now that physicists have learned to use the quantum state of electrons to perform a basic logical operation.
Decades from now quantum computers may crunch exponentially more numbers than their present-day counterparts. Their power would come from the weird fact that a quantum bit, or qubit, can exist as a 0 and 1 simultaneously. The most basic logical operation involving two qubits is to have one qubit switch the state of the other--or not, depending on its own state. For example, if the state of the first qubit represented 1, the state of the second would flip; but if the state of the first qubit were 0, the second would stay the same.
Such gates have been crafted already from qubits made of atoms. Physicists would like to do the same with easier-to-manufacture "solid-state" devices. In one such design, a superconducting circuit can enter a state in which an aluminum sliver, called a Cooper pair box, simultaneously does and does not contain an extra pair of electrons. Japanese researchers reported in February that a sequence of voltage pulses could entangle two such qubits, meaning that their two quantum states--Cooper pair present or not--mixed together (ScienceNOW, 22 February). However, the simplified controls couldn't put the qubits in all possible states.
Now the same group has taken the next step. In their new device, if the control qubit lacks a Cooper pair, a voltage pulse to the second qubit switches its state. If the control has a Cooper pair, the second qubit feels this presence through the entanglement and the pulse's effect is blocked. The key was adding a second voltage source so they could manipulate each qubit separately, report Tsuyoshi Yamamoto of the NEC Fundamental Research Laboratories in Tsukuba and the Institute of Physical and Chemical Research in Wako, Japan, and colleagues in the 30 October issue of Nature.
"The beautiful experiment they have performed is the first demonstration of a QUANTUM gate operation with a solid-state circuit," says Michel Devoret of Yale University, who works on a different type of superconducting qubit. "This is a remarkable step for quantum physics in general." The next step, he says, is to improve the success rate of the switch from the current 60%, by entangling the solid-state qubits completely.