A record number of six silicon-based spin qubits have been created by QuTech researchers, a partnership between the Delft University of Technology and TNO, in a fully interoperable array. Importantly, a new chip design, an automated calibration process, and new techniques for qubit initialization and readout allow the qubits to be operated with a low error rate. These developments will help create a silicon-based, scalable quantum computer. Today, Nature published the findings.
Qubits, the quantum equivalent of a bit in a classical computer, can be made from a variety of materials, but no one is certain which material will prove to be the most effective for creating a large-scale quantum computer. So far, only smaller silicon quantum chips with excellent qubit operations have been demonstrated. Under the direction of Prof. Lieven Vandersypen, scientists at QuTech have created a silicon chip with six qubits that operates with low error rates. This represents a significant advancement toward silicon-based fault-tolerant quantum computing.
Individual electrons are arranged in a linear array of six “quantum dots” that are separated by 90 nanometers to form the qubits. A silicon chip with structures that closely resemble the transistor, a basic element found in every computer chip, is used to create the quantum dot array. A qubit is defined by a quantum mechanical property called spin, and the orientation of the qubit determines whether it is in the 0 or 1 logical state. The team manipulated and measured the spin of individual electrons and made them interact with one another using precisely calibrated microwave radiation, magnetic fields, and electric potentials.
The first author, Mr. Stephan Philips, stated that there are two parts to the current quantum computing challenge. Creating sufficient-quality qubits and an architecture that enables the construction of large qubit systems Our work is appropriate for both groups. And given that creating a quantum computer is a massive undertaking, I believe it is fair to say that our contribution has gone in the right direction. ”
The spin of the electron is a delicate quality. The error rate rises as a result of tiny variations in the electromagnetic environment’s spin direction. The QuTech team developed new techniques for preparing, managing, and interpreting the spin states of electrons on top of their prior experience in engineering quantum dots. With this new qubit arrangement, they could instantly connect two or three electrons into a single system and build logic gates.
Superconducting qubits have been used to create quantum arrays with over 50 qubits. But it is the promise of a simpler transition from research to industry that makes silicon engineering infrastructure globally accessible. Prior to this work from the QuTech team, only arrays of up to three qubits could be engineered in silicon without compromising quality. Silicon presents certain engineering challenges.
“This study demonstrates that it is possible to increase the number of silicon spin qubits while maintaining the same level of precision. In the upcoming iterations of research, the key building blocks created could be used to add even more qubits, “said Dr. Mateusz Madzik, the co-author.
According to Prof. Vandersypen, “In this study, we push the limits of the number of qubits in silicon and achieve high initialization fidelities, readout fidelities, single-qubit gate fidelities, and two-qubit state fidelities. What is particularly noteworthy, though, is that we show all these qualities in one experiment using a record number of qubits.
