Optical control and readout of spins in enriched 28Si for applications in quantum information

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While the principles of quantum mechanics were discovered almost a century ago, there is a new and growing appreciation that they could lead to new ‘quantum technologies’ having spectacular potential for completely new and in some cases disruptive applications in communications, security, and computing. In a quantum computer (QC), superposition allows the conventional bit (0 or 1) to be replaced by an infinite range of superpositions of two states, giving a quantum bit, or qubit. Qubits can be linked using entanglement so that a measurement on one affects the outcome of a measurement on the other, even when they are completely separated. This defies our intuition, based as it is on macroscopic reality, but can be completely accounted for by quantum mechanics. It is now well understood that for certain classes of important problems, a QC using these properties could be enormously more powerful, and faster, than the largest imaginable conventional computer. This paradigm-shifting potential is fueling intense research around the world to find a technology for making a QC of sufficient complexity to solve this broad class of problems. A wide range of systems is being investigated, from photons to atoms to subatomic particles such as electrons and nuclear spins. Much activity is focused on semiconductor-based approaches, especially involving silicon (Si), which is the basis for our present computing and information technologies. It is hoped that the existing Si materials and nanoscale device technology could be harnessed to build a QC, if suitable qubits and the means of preparing, coupling and measuring them can be developed. Canada has strength in these areas, including the Institute for Quantum Computing in Waterloo, but ours is the only high-profile program focused on Si-based QI. Canada also has the only company currently selling QC technology, D-Wave Systems, of Burnaby BC. While the D-Wave computer is based on quantum annealing, and not the algorithmic approach first envisioned for constructing a ‘universal’ QC, it represents a very significant opportunity for Canadian science and technology. Our discovery that enriched 28Si has a unique property, namely, the linewidths of various optical transitions are much sharper in 28Si than in ordinary Si (or in any other semiconductor) led to new optical methods for controlling and measuring the electron and nuclear spins of impurities which are prime candidates for qubits in Si. These techniques have allowed us to measure coherence times - the time for which quantum information can be maintained - far beyond those of any other solid state system. We have recently used the optical methods developed in our lab to demonstrate coherent storage at room temperature for over 39 minutes – more than one thousand times longer than the previous record. Our results and new methods are receiving wide attention, and energizing an intense effort to realize a Si-based QC technology. The proposed program will capitalize on our achievements and collaborations, and continue to set new directions in this field. We will demonstrate that our optical methods can be used to work with new centers in Si allowing for greater complexity, and the testing of important QI concepts. We will explore systems selected for the possibility of using spins in Si for long term, retrievable storage of coherent information from superconducting qubit circuitry. We will also investigate other classes of defects that have the potential to lead to completely new approaches to QI in Si. This program will train future leaders, equipped with expertise in semiconductors, optics, cryogenics and quantum information theory, who will contribute to making the promise of quantum technologies a reality.