A program from the U.S. Defense Advanced Research Projects Agency (DARPA) claims to have achieved a major breakthrough in the field of quantum computing. The Optimization of Noisy Intermediate Quantum Devices (ONISQ) project has created the world's first quantum circuit with logical quantum bits (qubits).
Quantum computing is based on some seemingly magical or crazy concepts and has the potential to revolutionize our understanding of computers. By utilizing quantum effects and some relatively complex mathematical knowledge, quantum computing can increase the speed of information processing to several orders of magnitude that of classical computing, and promote the development of artificial intelligence, biochemistry, cryptography and other fields.
This is all very impressive, but has stumbled along the way, as getting quantum computing beyond the experimental stage has proven to be quite difficult. Part of the reason is that quantum computing has a very high error rate, which is not surprising because the principles of quantum computing are based on the fact that unlike the one and zero binary of classical computing, something can be a one, a zero, or both a one and a zero at the same time.
The trick is to find a way to make these error-prone or "noisy" processors more practical by combining them with classic systems. In DARPA's case, this involves focusing on solving optimization problems arising in defense and industry by developing logical qubits, a higher-level abstraction that acts like a quantum algorithm and is based on Rydberg qubits, which are physical components that act like two-state quantum systems.
"Rydberg qubits have the advantage of uniformity of properties - meaning each qubit behaves indistinguishably from the next," said Dr. Mukund Vengalattore, ONISQ program manager in DARPA's Office of Defense Science. "This is not the case with other platforms, such as superconducting qubits, where each qubit is unique and therefore not interchangeable."
"The homogeneity of Rydberg qubits allows them to be rapidly scaled, and also allows them to be easily manipulated and moved by lasers on quantum circuits. This overcomes the current error-prone approach of performing qubit operations by connecting them sequentially, thereby propagating errors throughout the chip. It is now possible to imagine dynamic reconfiguration of qubits on quantum chips that are no longer limited to sequential Running a quantum circuit. We can now use laser tweezers to bring an entire collection of qubits (all qubits) from one place in the circuit to another on the circuit, run an operation, and then put them back in their original location. "Dynamically reconfigurable and moveable Redburg logic qubits open up entirely new concepts and paradigms for designing and building scalable quantum computing processors."
Currently, DARPA has connected 48 logical qubits, but many more are needed to achieve the level of complexity required for practical quantum computers. However, this would be far less than the millions of qubits originally imagined required for a fault-tolerant quantum computer.
"If someone had predicted three years ago at the start of the ONISQ program that Rydberg (an excited atom with one or more electrons with a very high principal quantum number) neutral atom could serve as a logical qubit, no one would have believed it," said Dr. Guido Zuccarello, DARPA technical advisor.
This is DARPA's way of betting on the potential of these less-studied qubits and the more-studied ionic and superconducting circuits. As an exploratory program, ONISQ gives researchers scope to explore unique new applications beyond an optimization focus. Therefore, the Harvard-led team was able to harness more of the potential of these Redburg qubits and convert them into logical qubits, which is a very significant discovery.