We are currently living in an era of technological advancements. Among them, Quantum computation is getting much attention because of the advantages it carries within. A lot of research works are being carried out in the field of quantum computing and in silicon. But, what provides this much scope of research in this field? Well, let’s try to understand that. Computers that we use nowadays are working on the basis of classical laws whereas Quantum computers are based on quantum mechanics. The whole field of quantum computing relies on qubits (quantum bits) which are counterparts of bits in ‘classical computing’ (computing using laws in classical mechanics). Just like bits, qubits are also systems with the only difference that qubits are quantum systems. Therefore, in addition to the two states which acts as 0 and 1, superposition states (combination of both 0 and 1) are also possible here.
But, it is very difficult to maintain the qubits in quantum state. The quantum system acquires classical properties due to its interaction with the environment. So, before the required computing work is finished, the qubits may fall out of coherence (superposition) which affects the fidelity of the process. The overlap between the quantum state that is written into the memory and the state that is read out is called fidelity. To increase the fidelity, different systems are prepared and studied for their quantum coherence by different researchers. This is giving quantum computation notable importance in the research field along with a lot of other reasons.
Silicon in Quantum Computing
Among this invested research, silicon becomes a very significant material after three research studies have come out simultaneously and independently. The results of the studies were reported as:
- A team led by the University of New South Wales (UNSW) in Australia achieved 1-qubit operation fidelities up to 99.95 percent and 2-qubit fidelity of 99.37 percent with a three-qubit system comprising an electron and two phosphorous atoms, introduced in silicon via ion implantation.
- Another team from Delft University of Technology in the Netherlands led by Lieven Vandersypen achieved 99.87 percent 1-qubit and 99.65 percent 2-qubit fidelities using electron spins in quantum dots formed in a stack of silicon and silicon-germanium alloy (Si/SiGe).
- And finally, a team at RIKEN in Japan led by Seigo Tarucha similarly achieved 99.84 percent 1-qubit and 99.51 percent 2-qubit fidelities in a two-electron system using Si/SiGe quantum dots.
Even though the results were reported independently, there has been a circulation of methods, ideas and people between the teams. For example, the silicon and silicon-germanium material used by the Delft and RIKEN groups was grown in Delft and shared between the two groups. The isotopically purified silicon material used by the UNSW group was provided by Professor Kohei Itoh, from Keio University in Japan. The Sandia team worked directly with the UNSW group to develop methods specific for their nuclear spin system, but the Delft group was able to independently adopt it for their research too.
The UNSW and DELFT teams checked the performance of their quantum processors using a method called Gate Set Tomography (GST) which was developed at Sandia National Laboratories in the U.S. Gate Set Tomography (GST) is a protocol for detailed and predictive characterization of logic operations (gates) on quantum computing processors.
In addition to these, another study was published from Princeton University in which a two-qubit silicon or silicon-germanium processor was used to demonstrate state preparation and readout with fidelity greater than 97 percent, combined with single- and two-qubit control fidelities exceeding 99 percent. The operation of this quantum processor was also characterized using GST.
All these research results hints that silicon can turn out to be a significant material in the field of quantum computing.
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