Researchers from QuTech have made a significant breakthrough in the development of the “Andreev spin qubit,” positioning it as a promising contender in the quest for the ideal qubit. This groundbreaking advancement offers a more robust and inherently stable approach to creating qubits, surpassing previous iterations. By harnessing the strengths of two distinct qubit types, this new breed exhibits enhanced reliability and longevity. The team’s findings have been published in the esteemed journal Nature Physics.
In contrast to the realm of traditional computing, where bits rely on well-established and dependable technologies, the perfect qubit has remained an elusive goal. Will future quantum computers incorporate superconducting transmon qubits, silicon-based spin qubits, NV centers in diamond, or perhaps harness other quantum phenomena? Each variety of qubit carries its own set of advantages and disadvantages. Some prioritize stability, while others boast higher fidelity or ease of mass production. It is important to note that the perfect qubit has yet to materialize.
Best of both worlds
In a collaborative effort involving researchers from QuTech, a joint venture between Delft University of Technology and TNO, as well as international partners, a clever amalgamation of existing techniques was employed to store quantum information effectively.
Co-first author Marta Pita-Vidal elucidates, “Among the most promising contenders are spin qubits in semiconductors and transmon qubits in superconducting circuits. Nonetheless, each variant faces its own set of challenges. Spin qubits, for instance, possess compactness and compatibility with current industrial technology, but encounter difficulties in long-distance interactions. Conversely, transmon qubits exhibit efficient control and readout capabilities over extended distances, albeit with inherent operational speed limitations and a relatively larger size. This study endeavors to leverage the strengths of both qubit types by developing a hybrid architecture that amalgamates them.”
Andreev spin qubits
Arno Bargerbos, the other co-first author, explains, “Our experiment involved the direct manipulation of the qubit’s spin using a microwave signal. We achieved remarkably high ‘Rabi frequencies,’ indicating the speed at which the qubit can be controlled. Subsequently, we integrated this ‘Andreev spin qubit’ within a superconducting transmon qubit, enabling swift measurement of the qubit’s state.”
The researchers conducted a thorough examination of the Andreev spin qubit’s coherence time, which measures the duration for which the qubit remains viable. They observed that its “longevity” is influenced by the magnetic field generated by the surrounding materials.
Bargerbos adds, “Finally, we achieved the first direct strong coupling between a spin qubit and a superconducting qubit, facilitating controlled interactions between the two qubits. This breakthrough indicates that the Andreev spin qubit has the potential to serve as a crucial component in interconnecting quantum processors that rely on distinct qubit technologies, such as semiconducting spin qubits and superconducting qubits.”
Principal investigator Christian Andersen remarks, “Although the current Andreev spin qubit is not flawless, it still needs to demonstrate multi-qubit operations, which are essential for universal quantum computers. Additionally, the coherence time could be further improved by employing alternative materials. Fortunately, the scalability of these qubits aligns with semiconductor qubits, instilling hope that we can reach a stage where the quantum hardware ceases to be the limiting factor, and the focus shifts to developing quantum algorithms.”