Development of a solid-state quantum computer: Single electron transistors and highly charged ion implantation

Valery A. Zhukov

Arun Persaud, S.J. Park, Dieter H. Schneider +1 more

Andrew S. Dzurak, Lloyd C. L. Hollenberg, David N. Jamieson +13 more

We report a nanofabrication, control and measurement scheme for charge-based silicon quantum computing which utilises a new technique of controlled single ion implantation. Each qubit consists of two phosphorus dopant atoms ~50 nm apart, one of which is singly ionized. The lowest two energy states of the remaining electron form the logical states. Surface electrodes control the qubit using voltage pulses and dual single electron transistors operating near the quantum limit provide fast readout with spurious signal rejection. A low energy (keV) ion beam is used to implant the phosphorus atoms in high-purity Si. Single atom control during the implantation is achieved by monitoring on-chip detector electrodes, integrated within the device structure, while positional accuracy is provided by a nanomachined resist mask. We describe a construction process for implanted single atom and atom cluster devices with all components registered to better than 20 nm, together with electrical characterisation of the readout circuitry. We also discuss universal one- and two-qubit gate operations for this architecture, providing a possible path towards quantum computing in silicon.

Kohei M. Itoh

Michelle Yvonne Simmons, Steven R. Schofield, Jeremy L. O’Brien +8 more

Presents recent results on two different approaches to realize a solid-state quantum computer based in silicon, using phosphorus atoms as qubits. In the first approach the device is built from the 'bottomup' using a combination of atomic lithography with a scanning tunneling microscope and high quality silicon epitaxial growth using molecular beam epitaxy. In the second approach ion implantation is used to implant the phosphorus atoms from the 'top-down'. In both cases surface control electrodes are fabricated by conventional electron beam lithography. Techniques for qubit read-out utilising coincidence measurements on twin single electron transistors are also presented.

David N. Jamieson, F Splatt, CI Pakes +7 more

The construction of micro- and nano-scale electronic devices that exploit the properties of single atoms have been proposed. A very promising device is a silicon based solid state quantum computer based on an array of single 31P atoms as qubits in a pure 28Si substrate. Operation of the device requires independent control, coupling and readout of the state of individual qubits. We have developed a construction strategy for a few qubit device based on ion implantation of the qubits into prefabricated cells. An ion energy of less than 20 keV is necessary to ensure the ion range is at the required depth in the substrate which is of the order of 20 nm. Single ion impacts are registered by the electrical transient induced in an external circuit. Electron Beam Lithography fabricated cells, containing electrodes of the required nanometre scale, have been implanted with 14 keV 31P ions and the pulse height spectrum of single ion impacts has been successfully recorded. Discrimination on the pulse height allows rejection of ions that suffer unacceptable straggling. This opens the way to the rapid construction of a two qubit device in the first instance that will test many of the essential mechanisms of a revolutionary solid state quantum computer.