25 February 2013

Quantum Algorithm Performing True Calculation Developed

A team of researchers have demonstrated a working quantum algorithm that performs a true calculation for the first time.

An algorithm is any well defined computational procedures that takes some value or set of values as input and produces some value or set of values as output. A mathematical functions are a kind of algorithm where it performs a procedure to come out with a value based on a problem with a defined set of input value or values.

There are also non-computational algorithms, such as directions to calling a person on the phone. The steps are sequential from picking up the phone, getting the number, dialing the number, etc. etc.

But procedures should cover all possibilities and the subsequent action it must take. Going back to the phone call example, the algorithm should include steps for situations where the phone gets a busy signal or that the phone number cannot be found.

In short, algorithms must take all situations that could arise into consideration.

Classical Computers and Quantum Computers

There are three ways to make a computer work faster. One is to make more computers (using multiple computers for one activity). Another is to make new computers faster. And the third is to make algorithms that lets computer do things faster.

Without an algorithm behind a program or application, computers won't be able to perform as it should.

Current computers are called classical computers. At the heart of its processing power is the bit. The bit is the fundamental unit of information where it can be either of two values; 1 or 0. Stringing a series of bits together forms more complex values. The algorithms used for classical computers are also based on a step by step procedure, albeit millions of procedures in one second.

Quantum computers being developed are not based on the bit but on the qubit. A qubit (quantum bit), like the bit, is the fundamental unit of information for a quantum computer. Aside from being 1 and 0, the qubit can be in a superposition state where it is both 1 and 0. Quantum computers are able to perform all procedures in one step.

Classical algorithms will still work for quantum computers but it won't take full advantage of what a quantum computer will do.

A team of researchers have developed and demonstrated a working quantum algorithm that could pave the way for practical quantum computing.

Quantum Algorithms

An international research group led by scientists from the University of Bristol, UK, and the University of Queensland, Australia, has demonstrated a quantum algorithm that performs a true calculation for the first time. Quantum algorithms could one day enable the design of new materials, pharmaceuticals or clean energy devices.

The team implemented the 'phase estimation algorithm' — a central quantum algorithm which achieves an exponential speedup over all classical algorithms. It lies at the heart of quantum computing and is a key sub-routine of many other important quantum algorithms, such as Shor's factoring algorithm and quantum simulations.

Video: Computer Science - Algorithms

Dr Xiao-Qi Zhou, who led the project, said: "Before our experiment, there had been several demonstrations of quantum algorithms, however, none of them implemented the quantum algorithm without knowing the answer in advance. This is because in the previous demonstrations the quantum circuits were simplified to make it more experimentally feasible. However, this simplification of circuits required knowledge of the answer in advance. Unlike previous demonstrations, we built a full quantum circuit to implement the phase estimation algorithm without any simplification. We don't need to know the answer in advance and it is the first time the answer is truly calculated by a quantum circuit with a quantum algorithm."

Professor Jeremy O'Brien, director of the Centre for Quantum Photonics at the University of Bristol said: "Implementing a full quantum algorithm without knowing the answer in advance is an important step towards practical quantum computing. It paves the way for important applications, including quantum simulations and quantum metrology in the near term, and factoring in the long term."

The research is published in Nature Photonics.


University of Bristol
University of Queensland
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