Paving the road towards quantum computing
Quantum computers taking advantage of the superposition principle of quantum mechanics offer the unique potential to solve traditionally considered intractable problems. Information contained in interacting quantum bits will be stored and manipulated simultaneously, promising unprecedented parallel processing computer power for advanced simulations as well as unbreakable code encryption systems. In the search for inherently scalable quantum computer architecture, research work within the SQUBIT project demonstrated that superconducting nano-circuits are promising candidates for quantum bits of information. Flexibility in their design parameters can ultimately lead to large-scale, highly controllable coherent systems in the same way that the invention of transistor and integrated circuits presaged the development of networked conventional computers. An artificial two-level system, comprising Single cooper pair boxes (SCBs) in conjunction with an extremely sensitive electrometer, was fabricated at the Chalmers University of Technology and placed in superposition state by means of fast direct current (DC) pulses. These circuits are based on small superconducting islands weakly coupled to a charge reservoir via a Josephson junction. Therefore, their charge state was probed with a single electron transistor operated in radio-frequency mode (RF-SET). By varying the duration of the applied pulses researchers have succeeded in observing the temporal evolution of the quantum coherent oscillations, and measured dephasing and relaxation time. With further improvements on the measurement set-up better control over the temporal evolution of the superposition states is expected. This may well constitute one step further on the way to realise a functional quantum computer.
