First tunable, 'noiseless' amplifier may boost quantum computing, comm...( Researchers at the National Institut...)

Researchers at the National Institute of Standards and Technology (NIST) and JILA, a joint institute of NIST and the University of Colorado (CU) at Boulder, have made the first tunable noiseless amplifier. By significantly reducing the uncertainty in delicate measurements of microwave signals, the new amplifier could boost the speed and precision of quantum computing and communications systems.

Conventional amplifiers add unwanted noise, or random fluctuations, when they measure and boost electromagnetic signals. Amplifiers that theoretically add no noise have been demonstrated before, but the JILA/NIST technology, described in an Oct. 5, 2008, advance online publication of Nature Physics,* offers better performance and is the first to be tunable, operating between 4 and 8 gigahertz, according to JILA group leader Konrad Lehnert. It is also the first amplifier of any type ever to boost signals sufficiently to overcome noise generated by the next amplifier in a series along a signal path, Lehnert says, a valuable feature for building practical systems.

Noisy amplifiers force researchers to make repeated measurements of, for example, the delicate quantum states of microwave fieldsthat is, the shape of the waves as measured in amplitude (or power) and phase (or point in time when each wave begins). The rules of quantum mechanics say that the noise in amplitude and phase cant both be zero, but the JILA/NIST amplifier exploits a loophole stipulating that if you measure and amplify only one of these parametersamplitude, in this casethen the amplifier is theoretically capable of adding no noise. In reality, the JILA/NIST amplifier adds about half the noise that would be expected from measuring both amplitude and phase.

The JILA/NIST amplifier could enable faster, more precise measurements in certain types of quantum computerswhich, if they can be built, could solve some problems considered intractable todayor quantum communicatio
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