NATIONAL MAGNET LABORATORY

The Measurement Laboratories, located on the ground floor of the Newton Building at UNSW, house sophisticated experimental facilities for performing characterisation and measurements of nano-scale devices. The laboratory is supervised by Dr Andrea Morello, and serves as the primary lowtemperature measurement facility for the silicon qubit projects at UNSW.

The Measurement Laboratories, located on the ground floor of the Newton Building at UNSW, house sophisticated experimental facilities for performing characterisation and measurements of nano-scale devices. The laboratory is supervised by Dr Andrea Morello, and serves as the primary lowtemperature measurement facility for the silicon qubit projects at UNSW.

This 150 m2 laboratory contains equipment capable of measuring voltage signals in the pV range, from DC to 50 GHz microwave frequencies. These measurements can be performed at temperatures ranging from 30 mK to room temperature, at constant magnetic fields up to 10 T. The laboratory is at present equipped with three dilution refrigerators with various configurations to enable a wide range of measurements. The laboratory is supported by one full time professional staff with extensive experience in cryogenics and measurement systems.

The ‘DC’ dilution refrigerator is housed in an electrically screened room and is configured to allow highly sensitive measurements of two independent samples simultaneously using DC and low frequency AC measurements. This year, the DC fridge has received 8 additional thin coaxial lines, appropriate for time-resolved spin readout experiments.

Two ‘RF’ dilution refrigerators have been custom designed and configured to allow ultra-high speed measurements on picosecond timescales using radio frequency (200–600 MHz), fast pulse (30 ps) and microwave (0–50 GHz) techniques. RF fridge 1 is housed in a copper screened room. Supporting instrumentation includes: RF and microwave sources, cryogenic low noise amplifiers, two RF spectrum analyzers, a network analyzer and fast multi-channel oscilloscopes for data collection.

The microwave sources are used in conjunction with an AWG arbitrary waveform generator for pulsed local electron spin resonance experiments. In 2011, we have purchased and installed a new platform of PC-based AWG, pulse pattern and data acquisition cards to streamline the control and measurement of electron and nuclear spin qubits, and allow real-time data acquisition and feedback techniques. All setups have been provided with new ultra-low noise and high bandwidth current amplifiers. This new equipment allows detection of currents in the pA range with < 10 microseconds time resolution, or fA at low frequency.

Further work has been done to expand the ability to apply gate pulses and operate multi-qubit devices in all 3 fridges. The RF2 fridge has been completely rewired to allow control of 18-gate devices, and has been fitted with new microwave filters based on magnetically loaded Eccosorb material. Work is in progress to update the wiring and filtering of the RF1 fridge as well. Rapid characterisation of devices at liquid helium temperatures is achieved via seven device dipping probes which may be coupled to either of two comprehensive electronics racks under the control of data acquisition PCs, enabling a variety of standard device tests to be performed. The tests include: DC transport, RF/microwave measurements and magnetic field studies. A new wide-neck dipping dewar has been purchased and installed, to allow easy dipping of larger and multi-gate sample boards, including high-frequency experiments. There is a quiet space in the laboratory for data analysis and small meetings.