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Quantum Breakthrough: Two Qubit Calculations Performed

Researchers at Delft University of Technology in The Netherlands have succeeded in carrying out calculations with two quantum bits, the building blocks of a possible future quantum computer. The result was achieved by Ph.D. student Jelle Plantenberg in a team led by professors Kees Harmans and Hans Mooij.

The research took place within the FOM (Dutch Foundation for Fundamental Research on Matter) concentration group for Solid State Quantum Information Processing.

If realized, quantum computers could theoretically carry out tasks far beyond the abilities of all normal computers. In a quantum system, a quantum bit, also known as a qubit, exists in two states at the same time and the information from two qubits is entangled in a way that has no equivalent whatsoever in the normal world.

To be created, workable quantum computers will likely need to be produced using existing manufacturing techniques from the chip industry. Working on this basis, scientists at Delft University of Technology are currently studying two types of qubits: One type makes use of tiny superconducting rings, and the other makes use of "quantum dots," which are small devices that contain a tiny droplet of free electrons.

For the first time, a "controlled-NOT" calculation with two qubits has been performed with the superconducting rings. This is an important breakthrough because it allows any given quantum calculation to be realized.

In the "quantum dots" arena, the researchers are currently focusing on the coherent manipulation of individual electron spins isolated in single and coupled quantum dots, with the goal of realizing an elementary quantum computer in the solid state.

The Delft University of Technology research group studies electron transport through metal or semiconducting structures with critical dimensions of a few nanometers. The physics of electron transport in nanostructures is incredibly rich, and at low temperatures, quantum mechanical behavior emerges: The energy levels in the structures are quantized, just like in atoms and molecules. Their research focuses on understanding and controlling the quantum properties of structures such as superconducting rings, quantum dots, nanowires, and carbon nanotubes, with possible application to quantum computing and novel electronics devices.

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