Beating the standard quantum limit
As the integrated circuit components of conventional computers are rapidly approaching the so-called 'quantum limit', scientists have not been working on avoiding quantum effects. Instead, the opportunity to exploit them as a means of more effective computation was the main focus of research conducted by the SQUBIT-2 project partners. The intrinsic properties of quantum systems could enable quantum computers to perform parallel computations, to decrease processing time, and moreover to solve problems considered intractable for conventional computers. The unique potential of superconducting tunnel junctions to build sufficiently large, but still controllable systems of quantum bits (qubits) was explored at the laboratories of the Technische Universiteit Delft. In conventional computers, information is often stored as electrical charge on tiny capacitors. The presence or absence of charge on a single capacitor represents a bit, corresponding to the two different charge states. Remarkably, multiple qubits can be placed in a mixture of all possible states, a phenomenon known as entanglement. Complex manipulation of entangled states was for the first time reported by the SQUBIT-2 project partners. More specifically, a superconducting flux qubit, containing three in-line Josephson junctions was coupled to a superconducting quantum interference device (SQUID). The latter provided the measurement system for detecting quantum states, in addition to acting as a harmonic oscillator. By means of microwave spectroscopy, the entangled state generated could be controlled and the resultant Rabi oscillations of the coupled system detected. These research results provide strong evidence that solid state quantum devices could in the future be used as elements for the manipulation of quantum information.
