The quantum computer of the future will be able to carry out computations far beyond the capacity of today's computers. Quantum superpositions and entanglement of quantum bits (qubits) make it possible to perform parallel computations. Scientists and companies worldwide are engaged in creating increasingly better quantum chips with more and more quantum bits. QuTech in Delft is working hard on several types of quantum chips.
The core of the quantum chips is made of silicon. "This is a material that we are very familiar with", explained Professor Lieven Vandersypen of QuTech and the Kavli Institute of Nanoscience Delft. "Silicon is widely used in transistors and so can be found in all electronic devices." But silicon is also a very promising material for quantum technology. PhD candidate Guoji Zheng stated: "We can use electrical fields to capture single electrons in silicon for use as quantum bits (qubits). This is an attractive material as it ensures the information in the qubit can be stored for a long time."
Making useful computations requires large numbers of qubits and it is this upscaling to large numbers that is providing a challenge worldwide. "To use a lot of qubits at the same time, they need to be connected to each other; there needs to be good communication", explained researcher Nodar Samkharadze. At present the electrons that are captured as qubits in silicon can only make direct contact with their immediate neighbours. Nodar Samkharadze stated: "That makes it tricky to scale up to large numbers of qubits."
Other quantum systems use photons for long-distance interactions. For years, this was also a major goal for silicon. Only in recent years have various scientists made progress on this. The Delft scientists have now shown that a single electron spin and a single photon can be coupled on a silicon chip. This coupling makes it possible in principle to transfer quantum information between a spin and a photon. Guoji Zheng stated: "This is important to connect distant quantum bits on a silicon chip, thereby paving the way to upscaling quantum bits on silicon chips."
Lieven Vandersypen is proud of his team: "My team achieved this result in a relatively short time and under great pressure from worldwide competition." It is a true Delft breakthrough: "The substrate is made in Delft, the chip created in the Delft cleanrooms, and all measurements carried out at QuTech", added Nodar Samkharadze. The scientists are now working hard on the next steps. Lieven Vandersypen stated: "The goal now is to transfer the information via a photon from on electron spin to another."
This research was funded by an ERC Synergy Grant, NWO via the Nanofront Programme and Intel.
In a separate study published in the same issue ofScience, other researchers from the Kavli institute of Nanoscience at TU Delft also found a way to transfer spin information to photons.