These days, a lot of research is going on quantum computing. Engineers at University of New South Wales (UNSW), Sydney have developed something impressive – a new quantum computing architecture based on flip-flop qubit, which could make large-scale manufacturing of quantum processors a lot easier.
With this new design, silicon quantum processor could be scaled up without precise atom placement, which is required in other techniques. It allows qubits (or quantum bits) to be located hundreds of nanometers apart, while still remaining coupled.
Considering very large arrays of qubits, they need to be at a distance of 10 to 20 nanometers, or 50 atoms apart. If they are too far or too close, the entanglement between qubits (which makes quantum chips exceptional) does not occur.
The Radical New Architecture
The new “spin qubit” uses nucleus as well as electron of the atom. It can be controlled by electric signals rather than magnetic ones. Transferring electric signals are much easier than distributing magnetic signals within an electric chip.
To build an array of millions of qubits so close together, all the control lines and readout devices should be fabricated at nanometric scale, with that electrode density. The new concept, however, suggests an alternative.
Flip-flop qubit embedded in silicon matrix chip | Credit: Dr Guilherme Tosi
There are superconducting circuits and ion traps at the one end of the spectrum. These systems are quite bigger and easier to fabricate. Because of their bigger dimensions, in the long run, they might face issues while assembling and operating massive volume of qubits, as required by quantum algorithms.
“The new silicon based technique is easier to fabricate as compared to atomic-scale chips and still enables us to put a million qubits on a square millimeter” says Morello, quantum engineering professor at UNSW. ‘
The new design uses single-atom qubit, in which a silicon chip is coated with an insulated layer of silicon oxide. On top of this layer resides metallic electrodes, which operate at near absolute zero temperature, in the presence of powerful magnetic field.
Guilherme Tosi, who is lead author, has created a new type of qubit that uses both the electron and nucleus. These quantum bits (individually) have achieved the best-ever-observed coherence times. In this technique, a qubit ‘1’ state represents the electron spin is up and the nucleus spin is down, while qubit ‘0’ state represents the exact opposite scenario – electron spin is down and nucleus spin in up.
Researchers have given it a name, “flip-flop qubit”. In order to operate it correctly, one need to pull the electron slightly off from the nucleus, with the help of electrodes. This would generate an electric dipole. These dipoles then interact with each other over a thousand nanometer distance.
This enables single atom qubits to be placed at longer distance. There is enough space to distribute other key elements like readout devices, control electrodes and interconnects, while preserving qubit’s atom-like nature.
Flip flop’ qubit in an entangled quantum state | Credit: Tony Melov
However, this is only a theory proposal. Researchers do have some solid experimental data that indicate it is entirely practical, so they are working hard to completely demonstrate this.
The UNSW team has made a $83 million deal between UNSW, Australia’s Commonwealth Bank, Telstra (Australian telecommunications and media company), and the Australian and New South Wales government to build a 10 quantum bit silicon circuit prototype, by 2022. If everything goes well, this would be the world’s first silicon quantum computer.