In a big step forward in the field of quantum computation at the atomic scale, the scientists built the first two-bit gate between atoms in silicon, allowing the Qubits to communicate with each other and perform operations faster than ever before.
Because a two-bit gate is the basic construction element of a quantum computer, it has quite an amazing implication.
"Many people thought it would not be possible," said quantum physicist Michelle Simmons of the University of New South Wales (UNSW) in Australia.
Qubits are quantum bits and are a quantum equivalent of binary bits, basic units of information. However, when bits process information in one of two states – 1 or 0 – qubit may be in state 1, 0 or simultaneously, depending on their spin states.
The last state – 1 and 0 at the same time – is known as superposition.
As we informed earlier this year, maintaining qubits superposition allows quantum computers to solve complex mathematical problems by performing calculations based on the probability of the object's state before it is measured.
But for more efficient calculations we want qubits to communicate with each other. Hence the two-bit gate, which was achieved by the UNSW team only in 2015.
Technology has come a long way. Earlier this year, scientists were able to measure the accuracy of the operations of two qubits.
Now, by placing two qubits of atoms closer to each other than ever before, and by measuring and controlling their spin states in real time, another team led by Simmons reduced the time of a two-bit operation to just 0.8 nanoseconds.
It's 200 times faster than any other double-gate system developed so far.
"Atomic cubits have a world record for the longest cohorting times of qubit in silicon with the highest fidelity," Simmons said.
"Optimizing every aspect of the device's design with atomic precision has now allowed us to build a really fast, very accurate double-bit gate, which is the basic component of a scalable, silicon-based quantum computer."
It's a stunning job. First of all, the team had to work out the optimal distance to place two phosphor atoms for quantum operations. It turned out that it was only 13 nanometers.
Then they had to use a scanning tunnel microscope – an instrument designed for surface imaging at the atomic level – to place and close atoms in silicon with high precision, as well as the circuits required to control and read qubit's spin states.
The team could not only measure changes in qubits in real time, but also control how strongly they affected each other.
"We managed to bring the cubits of the city closer or further, effectively switching on and off the interaction between them, which is a prerequisite for quantum gates," said quantum physicist Yu He.
"The strict closure of qubit's electrons, unique in our approach, and the inherently low level of noise in our system enabled us to demonstrate the fastest two qubit goals in the existing silicon".
He added that it is great for sending information between two qubits. In conjunction with a single qigit gate, you can run any algorithm that you throw on it.
Theoretically, it is scalable. It will take some time to process it, but this achievement is a very important milestone that opens the door to this scalability.
"It was one of Michelle's last milestones to show that they can create a quantum computer using atomic qubits," said Emma Johnston, the University dean of UNSW.
"Their next major goal is to build a 10-qit quantum integrated circuit – and we hope to achieve it within 3-4 years."
Research has been published in Nature.