Quantum states preserved longer

Microwave pulses enabled control over the system

April 18, 2013 02:53 am | Updated 02:53 am IST

Classical computers use electronic devices called transistors to perform mathematical operations with input electric signals. Because of transistors’ technical limitations, classical computers take exponential amounts of time to solve more complex problems.

The difference

A quantum computer, on the other hand, uses the exotic properties of extremely tiny particles like electrons to perform operations much faster than a classical computer would, “trapping” the particles into controllable states called quantum systems.

However, these systems last for extremely short spans of time while being manipulated before destabilising. As Abdufarrukh Abdumalikov, a scientist at the Quantum Device Lab (QDL) at ETH, Zurich, emailed this Correspondent: “In reality, quantum systems are coupled to their environments and have a short memory, i.e. decoherence, which hinders us from observing their effects.”

To resolve this, a team of researchers from QDL, including Abdumalikov, have proposed the use of special circuits. “We manipulate our quantum circuit much before it decoheres,” Abdumalikov explained.


These circuits contain superconducting components – where an electric current can flow sans resistance – that work to preserve quantum states for longer durations, such as for several millionths of a second.

Once they are made to last for so long, the circuits are struck with short microwave pulses which modify the systems of particles to perform calculations.

The team’s results appeared today (April 18) in Nature .

Apart from assistance from superconducting components, the researchers also used a geometrical concept to delay the destabilisation.

Under the guidance of Stefan Filipp, a member of the study, the researchers applied microwave pulses in a precise sequence to “move” the quantum state through its Hilbert space.

The Hilbert space is the “natural habitat” of any quantum system, just like ours is three-dimensional space.

Eventually, the team was able to ease the system into some degree of stability and exercise very specific control over it – whether to study the process through which it formed or to use it as a rudimentary computer.

The QDL researchers’ work is part of a very active field of research and development. This is because quantum computers, at least on paper, promise to be much faster than even classical supercomputers without costing as much.

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