MIT researchers have achieved a significant breakthrough in quantum computing by demonstrating a novel quantum circuit architecture that can perform qubit logic gates with record-breaking levels of accuracy. The advance brings the field closer to implementing quantum error correction, which is essential for realizing practical, reliable quantum computers.
Future quantum computers hold immense promise for solving complex problems beyond the reach of even today’s most powerful supercomputers. However, quantum systems are intrinsically prone to errors. To overcome this, quantum error correcting codes are required, which can detect and account for qubit errors provided gate operations in a quantum circuit exceed a minimum fidelity threshold.
The new architecture developed by the MIT team achieved two-qubit quantum logic gate fidelities exceeding 99.9% and single-qubit gate fidelities reaching 99.99% – well over the error correction limits. This was enabled by using ‘fluxonium’ qubits coupled in an innovative circuit design.
Fluxonium Qubits Offer Longer Lifetimes
The breakthrough utilizes fluxonium qubits, which have significantly longer lifetimes or ‘coherence times’ compared to widely used transmon qubits. This coherence time reflects how long a qubit can maintain quantum coherence while performing operations. Fluxonium qubits demonstrated coherence times over 1 millisecond – 10 times longer than typical transmon qubits.
Longer coherence enables higher gate fidelities, as qubit errors accumulate when operations take too long. But it was unclear if fluxonium’s advantages could be harnessed in multi-qubit gates. The MIT team overcame this by using a clever fluxonium-transmon-fluxonium (FTF) coupling architecture.
Novel Circuit Suppresses Qubit Errors
Their design links two fluxonium qubits using a tunable transmon coupler. This enabled strong qubit interactions while suppressing unwanted background noise that typically increases with stronger couplings. The persistent noise, known as ZZ interactions, can introduce errors.
The combination of fluxonium’s long coherence and the FTF coupling produced the record-high gate fidelities demonstrated. These far exceed required error correction limits, a pivotal milestone on the path to fault-tolerant, scalable quantum computing.
Lead author Leon Ding explains that adding redundant qubits can enhance overall system robustness, provided the individual qubits surpass an accuracy threshold. Noisy qubits accumulate too many errors. But the high-fidelity fluxonium qubits cross this quantum advantage threshold for the first time.
Bringing Quantum Error Correction Within Reach
Correcting errors will require millions of physical qubits. However, the fewer initial errors, the lower the overhead. By squeezing maximum performance from each qubit, the MIT approach brings this goal closer to reality.
The team collaborated with MIT Lincoln Laboratory experts to optimize the qubit fabrication process and infrastructure for extending to larger scales. Recently, Ding and colleagues founded the startup Atlantic Quantum to build commercial fluxonium-based quantum systems.
Ding says the next step is expanding their architecture to more interconnected qubits. While universal quantum computers remain years away, this breakthrough demonstrates a promising new path forward. For researchers confident in fluxonium’s superiority over transmons, it represents a pivotal leap.
Advancing From Quantum Proofs-of-Concept
In the race to achieve the immense computational power promised by quantum technologies, progress must come through high-fidelity quantum building blocks. Over two decades, demonstrations have advanced from isolated quantum phenomena to proto-computers operating toy algorithms.
This new qubit architecture propels the field beyond proof-of-concepts towards engineering practical machines. Early quantum advantage will likely emerge through hybrid systems integrating quantum co-processors into classical computers. The fluxonium innovation may accelerate this transition across the second quantum revolution’s most daunting threshold.