Tuesday 28th February 2012

They have established three new records for retaining the integrity of quantum mechanical properties inquantum bits, or qubits, reducing errors in elementary computations that brings them closer to minimum requirements for a full-scale quantum computing system that will move computing up a generational level. *Right: Courtesy: Nature*

IBM has chosen to employ superconducting qubits, using established microfabrication techniques developed for silicon technology, providing the potential to one day scale up to and manufacture thousands or millions of qubits.

The special properties of qubits will allow quantum computers to work on millions of computations at once, while desktop PCs can typically handle minimal simultaneous computations. For example, one 250 qubit state contains more bits of information than there are atoms in the universe.

These properties will have wide-spread implications foremost for the field of data encryption where quantum computers could factor very large numbers like those used to decode and encode sensitive information.

"The quantum computing work we are doing shows it is no longer just a brute force physics experiment. It's time to start creating systems based on this science that will take computing to a new frontier," says *(left)* IBM scientist Matthias Steffen, manager of the IBM Research team that's focused on developing quantum computing systems to a point where it can be applied to real-world problems.

Potential applications include searching databases of unstructured information, performing a range of optimisation tasks and solving previously unsolvable mathematical problems.

**QUANTUM SUPERPOSITION**

The most basic piece of information that a typical computer understands is a bit. Much like a light that can be switched on or off, a bit can have only one of two values: "1" or "0". For qubits, they can hold a value of “1” or “0” as well as both values at the same time. Described as superposition, this is what allows quantum computers to perform millions of calculations at once.

One of the great challenges for scientists seeking to harness quantum computing is controlling or removing quantum decoherence – the creation of errors in calculations caused by interference from factors such as heat, electromagnetic radiation, and materials defects.

To deal with this, scientists have been experimenting for years to discover ways of reducing the number of errors and of lengthening the time periods over which the qubits retain quantum mechanical properties. Sufficiently long, error correction schemes become effective making it possible to perform long, complex calculations.

Many viable systems can potentially lead to a functional quantum computer. IBM is focusing on using superconducting qubits to allow a more facile transition to scale up and manufactur.e It has recently been experimenting with a unique “three dimensional” superconducting qubit (*right 3D qubit*), an approach initiated at Yale University.

Among the results, the IBM team has used a 3D qubit to extend the amount of time that the qubits retain their quantum states up to 100 microseconds – an improvement of 2 to 4 times over previously reported records. This value reaches just past the minimum threshold to enable effective error correction schemes suggesting scientists can begin to focus on broader engineering aspects for scalability.

In separate experiments, the group at IBM also demonstrated a more traditional “two-dimensional” qubit (*left 2D qubit*) device and implemented a two-qubit logic operation – a controlled-NOT (CNOT) operation, a fundamental building block of a larger quantum computing system.

Their operation showed a 95% success rate, enabled in part due to the long coherence time of nearly 10 microseconds. These numbers are on the cusp of effective error correction schemes and greatly facilitate future multi-qubit experiments.

**IBM LOOKS AT SYSTEMS INTEGRATION & HYBRID CLASSICAL:QUANTUM**

The implementation of a practical quantum computer poses tremendous scientific and technological challenges, but all results taken together paint an optimistic picture of rapid progress in that direction.

Core device technology and performance metrics at IBM have undergone a series of advancements by a factor of 100 to 1,000 times since the middle of 2009, culminating in the recent results that are very close to the minimum requirements for a full-scale quantum computing system as determined by the world-wide research community. In these advances, IBM stresses the importance and value of the ongoing exchange of information and learning with the quantum computing research community as well as direct university and industrial collaborations.

“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. 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,” notes David DiVincenzo, (*right*) professor at the Institute of Quantum Information, Aachen University and Forschungszentrum Juelich.

Based on this progress, optimism about superconducting qubits and the possibilities for a future quantum computer are rapidly growing. Most of the work in the field to date has focused on improvements in device performance, efforts in the community now must now include systems integration aspects, such as assessing the classical information processing demands for error correction, I/O issues, feasibility, and costs with scaling.

IBM envisions a practical quantum computing system as including a classical system intimately connected to the quantum computing hardware. Expertise in communications and packaging technology will be essential at and beyond that presently practiced in developubg today’s most sophisticated computers.

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