– 21 –
at JyU on microwave properties of nano-structured materials and quantum coherence effects in superconducting devices based on the Josephson effect.
CONTROL OF SUPERCONDUCTING QUBITS
Khattiya Chalapat, Jian Li, and Sorin Paraoanu
We have studied a system consisting of a superconducting coplanar waveguide resonator capacitively coupled to two charge qubits. The resonator can be read out using a single Josephson junction. Using the simulated annealing method, we show that any two-qubit gate can be implemented by a suitable combination of microwave pulses with relatively large fidelities. We propose a quantum non-demolition (conditional) method to read out the qubits: we show that an entangled state is established between the qubits when no photon leaks out of the resonator, while for a generic microwave drive we characterize the photon-qubit-qubit entanglement.
MICROWAVE PROPERTIES OF NANOCOMPOSITES
Khattiya Chalapat, Jian Li, Sorin Paraoanu, and Kari Sarvala
Collaborators: University of Notthingham
Measurements of the S-parameters and calculation of the corresponding complex electromagnetic permittivity and permeability were done by the Nicholson-Ross-Weir method using a 18 GHz airline and custom-made and home-made toroidal samples. The samples measured were composites containing Co, Ni, and Au nanoparticles.
Collaborator: Prof. J. Korppi-Tommola, Univ. of Jyväskylä
We have measured the IV characteristic and dI/dV at various bias voltages for a device combining the structure of a solar cell with that of a photodiode. We characterize the device under different illuminations and we point out that it can be used as a phototransistor.
Elias Pentti, Juho Rysti, Anssi Salmela, Alexander Sebedash, and Juha Tuoriniemi
Much of the experimental activity at the YKI cryostat this year was aimed to solve the technical shortcomings of the adiabatic melting experiment run previously. New superfilter filling lines were tested and a satisfactory result in terms of adiabatic flow was achieved. However, even more effort will be put to control the growth and melting of the solid phase in the cell without disturbances arising from the connection to warmer environment by assembling a bellows actuator system, where the fluid commuting to and from the cell will never be warmer than 10 mK.
Probing the state of the fluid under investigation by quartz fork oscillators was studied in order to replace the vibrating wire resonators in the experimental cell. The prospects for using such sensors for a variety of studies in the physics of helium liquids seem superb.
During these test measurements significant amount of data on the properties of helium mixtures at low temperatures were collected also. First, we determined for
Annual Report 2007