With quantum bits that last long enough to do actual work, IBM hopes extremely fast computers are on their way
IBM has achieved major breakthroughs toward the construction of full-scale quantum computers that could be vastly more powerful than today’s machines.
The company has established a new record, keeping a quantum bit or “qubit” in a coherent quantum state for 100 microseconds, bringing the researchers closer to doing actual computational work with the systems. The findings are to be presented this week at the annual American Physical Society meeting in Boston, Massachussetts.
Qubits are the basic units carrying information in quantum computing. Like the bits used in current computers, they have a value of 1 or 0 but they actually have both values at the same time, thanks to a phenomenon called “superposition”.
In the world of minute particles, superposition happens all the time, but it can only happen when a system is isolated from all outside interactions and observation, and this is virtually impossible at the scale of everyday objects, or even tiny transistors.
In Schrodinger’s famous thought experiment, a cat is imagined in a box, whose status is a superposition of “alive” and “dead”, until the box is opened and the cat is observed.
The absurdity of Schrodinger’s cat illustrates the difficulty of creating coherent quantum systems, but quantum computing researchers are attempting to create isolated qubits and keep them isolated and coherent long enough to perform actual work.
In theory, a coherent quantum computer can simultaneously process all possible inputs, by superposing them. A single 250-qubit state – if one could be c onstructed and isolated from outside observ ation – would handle more bits of information than there are atoms in the universe, IBM said.
IBM said it expects quantum computers to have a particular impact on data encryption, since they have the ability to factorise very large numbers quickly. Quantum computers could also be useful for searching databases of unstructured information and solving previously unsolvable mathematical problems, IBM said.
IBM is concentrating on superconducting qubits, which have the advantage of using the manufacturing techniques already developed for silicon technology, meaning they are that much closer to mass production.
“The quantum computing work we are doing shows it is no longer just a brute force physics experiment,” said IBM scientist Matthias Steffen in a statement. “It’s time to start creating systems based on this science that will take computing to a new frontier.”
IBM’s breakthroughs deal with the challenge of minimising the errors in calculations caused by interference from factors such as heat, radiation and materials defects, called quantum decoherence. Interference from the outside ends superposition, and causes the quantum system to settle into one state or the other.
To perform any real calculations ts researchers must keep the qubits in a state of superposition for longer times, to the point where error correction schemes can be applied.
One of the company’s results was the use of a “three-dimensional” superconducting qubit, or 3D qubit (pictured), to extend the amount of time that qubits retain their quantum states up to 100 microseconds, two to four times better than previously reported records.
This figure is just over the minimum threshold needed to allow effective error correction schemes, IBM said.
In another experiment IBM demonstrated a two-dimensional qubit device implementing one of the fundamental quantum computing operations, called a controlled-NOT (CNOT) operation, which showed a 95 percent success rate and a coherence time of nearly 10 microseconds.
These figures also are on the edge of allowing effective error correction schemes to come into play, IBM said.
While IBM predicts it will be another 10 to 15 years before quantum computers become viable, it said the advances show significant progress. The company said it is continuing to work with researchers at other institutions on the technical and manufacturing challenges involved.
“The superconducting qubit research led by the IBM team has been progressing in a very focused way on the road to a reliable, scalable quantum computer,” said David DiVincenzo, professor at the Institute of Quantum Information, Aachen University and Forschungszentrum Juelich, in a statement. “The device performance that they have now reported brings them nearly to the tipping point; we can now see the building blocks that will be used to prove that error correction can be effective, and that reliable logical qubits can be realised.”
In January scientists demonstrated how quantum computers could be used to improve the security of cloud computing.
The research, carried out by Vienna Centre for Quantum Science and Technology (VCQ) at the University of Vienna, showed that a technique called “blind quantum computing” can be extended to cloud services, such as Google Docs, but crucially for businesses without the loss of security. This is because the so-called blind quantum computing can be carried out without a cloud computer ever knowing what the data actually is.
Also last month researchers at Cambridge University said they had created a “quantum fluid” that could be a breakthrough in the development of quantum computers.
The Cambridge University scientists built a semiconductor chip that uses lasers to generate particles exhibiting such phenomena, but on a much larger scale than usual – so large that they are visible to the human eye. The team named their particles “polaritons”.
The polaritons behave like superconductors and demonstrate classic quantum pendulum states, and the scientists found they could control the particles’ movements by moving the position of the laser beams.
The team said they could increase the number of laser beams to create more complicated quantum states.
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