Cluster State Quantum Computer Using Deutsch's Algorithm

It is widely believed that if large-scale quantum computers can be built, they will be able to solve certain problems exponentially faster than any classical computer. Finding a way to build such a computer that works more efficiently than a classical computer has been the holy grail of quantum information processing for more than a decade.

A quantum computer is any device for computation that makes direct use of distinctively quantum mechanical phenomena, such as superposition and entanglement, to perform operations on data. In a classical (or conventional) computer, the amount of data is measured by bits; in a quantum computer, the data is measured by qubits (Quantum bits). The basic principle of quantum computation is that the quantum properties of particles can be used to represent and structure data, and that quantum mechanisms can be devised and built to perform operations with these data.

Mark Tame, author of an article titled, "Experimental Realization of Deutsch's Algorithm in a One-Way Quantum Computer", states that, together with a team of researchers, he achieved "The first implementation of Deutsch's Algorithm for cluster states in quantum computing,"

The Deutsch-Jozsa algorithm is a quantum algorithm, proposed by David Deutsch and Richard Jozsa in 1992. It was one of first examples of a quantum algorithm, designed for execution on quantum computer applications, that has the potential to be more efficient than classical algorithms by taking advantage of quantum superposition and entanglement.

"When performing a quantum algorithm," says Tame, "the standard approach is based on logical gates that are applied in a network similar to classical computing." Tame points out that this method of quantum computing is not practical or efficient. "Our quantum computer model uses cluster states, which are highly entangled multi-partite quantum states."

The group's quantum computer makes use of four entangled photons in a cluster state.

Tame explains how it works: "Our setup is completely based on light, where quantum information is encoded on each photon. The information is in the polarization of each photon, horizontal or vertical, and superpositions in between. An ultra-violet laser pumps a crystal and produces an entangled pair of photons in one direction. The laser beam then hits a mirror and bounces back to form another pair of entangled photons on its second passage through the crystal. These four photons are then made to interact at beamsplitters to form the entangled cluster state resource on which we perform the quantum computation."

To perform the computation, he says that "We perform Deutsch's Algorithm as a sequence of the measurements. When you measure in a specific basis, you can manipulate the quantum information in the photons using their shared entanglement." He continues with an illustration related to classical computing: "You can think of the cluster state as the hardware , and the measurements as the software ."

Though for now it is "[...] really just a proof of principle [...]", they demonstrated it can be done, so the next step will be to build larger clusters states and perform more useful computations.