Scientists at the Massachusetts Institute of Technology have presented an alternative superconducting qubit architecture that has a longer operating time and is less sensitive to errors. These are two important features that could lead to general-purpose commercial quantum computers. The architecture has been tested in one- and two-qubit circuits, proving its promise.
Modern quantum computers from Google and IBM in superconducting qubits use so-called transmonium qubits to build logic elements. These qubits are based on a Josephson junction that operates at a single frequency. About ten years ago, qubits based on double-frequency Josephson junctions were proposed. Architecturally, transmonium qubits can be considered single, while fluxonium qubits are associated with groups – chains in which there are many or even many Josephson junctions. In these groups, low-frequency flownium qubits are used to store quantum states (qubits), and high-frequency ones are used for logical operations (gates).
Over time, it has been shown that flownium qubits are able to maintain the qubits in a coherent state for approximately an order of magnitude longer, allowing time to create logical circuits. operation with a lower error rate than in the case of transmonium qubits. Thus, one of the works this summer showed that the lifetime of a flownium qubit reached 1.43 ms. Until recently, experts have done little work on flownium, but its unique qualities cannot be ignored – it may be the shortest path to productive and scalable universal quantum computers.
A fault-tolerant quantum architecture in which a transmonium qubit combines two flownium qubits. Image source: American Physical Society
In new work, MIT researchers have shown how to increase the reliability (noise immunity) of flownium qubits. The fact is that the strong bond formed between flownium qubits in the chain, in addition to useful properties, also led to an increase in the influence of errors. So, scientists actually fuse fluxonium qubits with transmoniums by inserting a transmonium element between two fluxoniums.
The studies conducted for one and two qubit fluxonium circuits showed that the accuracy of two qubit gates based on the new architecture reached 99.9%, and the one qubit gate reached a record value. which is 99.99%, as described by scientists in an article in the journal Physical Review X.
