- Solid-state implementations for quantum information processing (QIP)
- Single-electron devices for spin-based QIP
- Quantum nanoelectronics, quantum transport
- Methods of coherent control
Laboratory equipment and facilities
- State-of-the-art “dry” dilution refrigerator installed June 2009, base temperature as low as ~ 8 mK
- Cooling power: 250 μW at 100 mK
- 8 T superconducting magnet
- Optical access
- Janis 1.5 K wet He cryostat and magnet system for device testing
- Electronic probe station (room temperature)
- UW’s Nanofab clean room facility
- Raith 150-TWO electron beam lithography and SEM
- e-beam evaporators (metal deposition), reactive ion etching, photolithography, etc.
A student using the probe station to perform a test of nanowire conductance.
Insert of the Oxford VeriCold DR200 dilution refrigerator system. The bottom plate holds the He3-He4 mixing chamber and reaches base temperature. Sequentially, the upper plates are the 80 mK plate, the still plate, the 4 K plate, and the 70 K plate.
Nanowire-based tunable quantum dots
A quantum dot is a nano- or meso-scopic electrostatic potential well that allows a small number of electrons (as few as one) to be confined. We would like to use the spin of a single electron as a quantum bit (qubit), and to arrange these qubits together scalably to form building blocks for large-scale quantum information processors.
A one-dimensional array of tunable quantum dots can be defined by placing a set of fine gate electrodes along a semiconductor nanowire. Typical nanowire diameters are in the range of 30 to 70 nm, and electrodes approximately 20 nm in width can be fabricated using standard electron beam lithography and lift-off techniques. We aim to use the same set of gate electrodes to both define the dot potentials and to implement one- and two-qubit quantum manipulations.
A prototype bottom-gated device fabricated at Waterloo is shown below (false color image). The device is based on an InAs nanowire. InAs possesses a number of properties that make it an attractive material for our experiments: small effective electron mass for enhanced confinement, strong spin-orbit interaction that can be used to drive spin resonance with electric fields, and a large electron g-factor yielding large spin (Zeeman) splittings at modest magnetic fields.
In collaboration with R. R. LaPierre, McMaster University.
Electron spin resonance: control of hyperfine coupled electrons and nuclear spins
Another testbed for quantum control is bulk magnetic resonance – in particular, we are interested in systems in which electrons and nuclei are coupled through the hyperfine interaction. Due to the larger gyromagnetic ratio of the electrons compared to nuclei, faster quantum gates and higher spin polarization can be achieved than in standard NMR approaches. Control of the electron spin can be used as a bus to perform quantum operations between nuclei using their hyperfine coupling to the electron. In fact, an anisotropic hyperfine coupling to each nucleus allows for universal control of the 1 electron + n nuclear spin system by applying a suitably modulated microwave field.
At left is a model of the malonic acid molecule. After gamma or X-ray irradiation, one of the CH2 hydrogen atoms is removed and an unpaired electron is left in its place. The wavefunction of the electron overlaps with the hydrogen (spin-1/2 nucleus), giving rise to a hyperfine coupling between the two spins. If the central carbon is 13C labeled, it will also have spin-1/2 and be coupled to the electron. The coupling strengths depend on the orientation of the sample with respect to the external magnetic field. With proper orientation of the single crystal sample, anisotropic couplings can be found so that the nuclei can be efficiently controlled via the electron. This 1 electron + 2 nuclear spin system is currently being used as a testbed for quantum control.
The home-built X-band ESR spectrometer is shown at right. It consists of an electromagnet, cryostat, and suite of microwave components. Experiments are controlled by home-written software, allowing great flexibility. Microwave pulses are shaped by an arbitrary waveform generator (1 ns resolution) and corrected in-situ for non-linearities by a special antenna / feedback circuit. The cryostat / sample resonator design allows the sample to be oriented in-situ and to be cooled to liquid helium temperatures, while maintaining the resonator at room temperature for large bandwidth of excitation.
In collaboration with Ray Laflamme.
|Interested in a Masters or PhD project?
Highly motivated students are currently being sought. Group projects involve:
Students will gain both hands-on and theoretical experience across a number of traditional fields, e.g. Physics, Chemistry, Materials Science and Electrical Engineering. Firm theoretical grounding (especially quantum mechanics), good experimental aptitude and creativity are desirable qualities.
Undergraduate 4th year projects
Projects related to our research on quantum information and its implementations are available for CHEM 494 and PHYS 437
Contact: baugh [at] iqc.ca