Spatial adiabatic passage techniques in mesoscopic quantum electronic systems

© 2010 Dr. Lenneke Maria JongAdiabatic passage techniques have been used for coherent population transfer in quantum optical systems. Coherent Tunnelling Adiabatic Passage (CTAP) extends one such technique, the well known STIRAP protocol, into a spatial context. It transports a particle coherently using a counter-intuitive coupling sequence of tun- nel matrix elements. Working in the spatial regime affords us the opportunity to tailor the Hilbert space by controlling the spatial location of states and hence the topology of the resulting quantum network. These techniques provide opportunities for observing and exploring new physics and are applicable to the success of quan- tum information and other quantum technologies. This thesis looks at extensions of adiabatic passage on a number of topics. Particularly, the Alternating coupling scheme variant of the CTAP protocol (ACTAP), and its use in a number of proposed devices, is examined. We show that the ACTAP protocol is robust to variations in device parameters away from ideal conditions. We look at the modelling of a semi- realistic device using phosphorus donors buried in silicon using industry-standard semiconductor device modelling software in combination with quantum mechanical calculations to incorporate parameters needed when considering experimental imple- mentations of this device. Through these calculations we estimate the time required for adiabatic operation of a five donor ACTAP device is approximately 70ns, within measured spin and estimated charge relaxation times. The use of ACTAP in an electron interferometer geometry is then explored. This device shows an interesting interplay between adiabatic and non-adiabatic behaviour, including regimes which are analogous to the electrostatic Aharonov-Bohm effect. An extension of this de- vice, with two coupled interferometers, is explored, motivated by Hardy’s Paradox. Finally the effect of continual measurement of one of the CTAP sites on the fidelity of the protocol is examined. Phenomenological models of decoherence in a three site CTAP device are investigated. We also look at how both periodic and random changes in the on-site energy of one of the dots throughout the CTAP process, as would be induced by a measurement device such as an SET, will affect the fidelity. We link the models developed here with the characteristics of real experimental de- vices. These calculations show that the effect on the fidelity depends on which site is measured and the frequency of the measurement signal