#Physicsqubits

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Superconducting Quantum Materials And Systems Center

Superconducting Quantum Materials and Systems Centre Superconducting Quantum Materials and Systems (SQMS) Centre, a DOE National Quantum Information Science Research Centre based at Fermilab, is developing scalable quantum computing and communication technologies.

SQMS researchers integrated advanced materials science with Fermilab's accelerator technology skills to make substantial progress. The longest-lived multimode superconducting  quantum processor unit (QPU)  yet created has a coherence lifetime of almost 20 milliseconds. By overcoming typical superconducting platform limits, this discovery will revolutionise quantum computing.

The SQMS Centre aims to understand and eliminate decoherence mechanisms in superconducting 2D and 3D devices. Coherence time, which defines how long a qubit can maintain its quantum state without outside noise, underpins quantum computing, sensing, and communication. SQMS is expanding this key metric through excellent materials science and the intricate integration of superconducting quantum cavities with industry-made computer circuits.

Unique Method Based on Particle Physics

The innovative SQMS technique uses a superconducting qubit device inside a 3D SRF cavity. These complicated systems are chilled to extremely low temperatures, often 10–20 millikelvin (mK), to shield microwave photons from external disturbances and lengthen their lives. To generate, alter, and read quantum states, this precisely regulated system is needed.

Performance, Scalability Unseen Image SQMS has marked quantum computing milestones. Chip-based transmon qubits, a charge qubit circuit with decreased noise sensitivity, have shown consistent coherence increases and record-breaking lifetimes of over a millisecond. With the transmon chip as a central logic-capable quantum information processor and the microwave photons inside the 3D SRF cavity as random-access quantum memory, these transmon qubits form the “nerve centre” of the platform, creating a novel quantum analogue to classical computing architecture.

The longest-lived multimode superconducting QPU, with a coherence lifespan of over 20 milliseconds, is impressive. This performance is much better than standard superconducting platforms, which typically take 1 or 2 milliseconds. Over the qubit lifetime, this two-cell SRF module and superconducting transman enable 10,000 high-fidelity operations.

Yao Lu, an associate scientist at Fermilab and co-lead for QPU connectivity and transduction in SQMS, said, “We have achieved ultra-high-fidelity single-photon entangling operations between modes [>99.9%] and demonstrated the creation of high-fidelity [>95%] quantum states with large photon numbers [20 photons].” This development will enable scalable, error-resistant quantum computing.

The “pay-off is scalability,” says Fermilab senior scientist Alexander Romanenko, who leads the SQMS quantum technology development. He finds that a logic-capable transmon processor qubit can link to many cavity modes acting as memory qubits in a single-cell SRF cavity, potentially controlling over 10 qubits. As qubits increase, this new technology drastically reduces microwave channels needed for system control. Romanenko emphasises the advantages of employing quantum states in SRF cavities, which have longer coherence lengths (up to two seconds) and higher quality factors than transmons' milliseconds.

Betting on Qudits for Information Density

The SQMS bets on scalable “qudit-based” quantum computation and communication. Multilayer qudits can store more than two states, providing more information than two-state qubits. This strategy increases information processing capability with fewer quantum units, which may improve calculations. This architecture's core physics allow quantum entanglement and coherent quantum information transfer between the transmon qubit and SRF cavity discrete photon modes. SQMS scales up to a multiqudit QPU system using parallel routes and modular computation. These include:

Using a two-cell SRF cavity quantum processor and a nine-cell multimode SRF cavity as memory.

Only two-cell modules are used.

Construction materials can include custom multimodal cavities with ten or more modes.

The initial QPU prototypes will be tested and optimised by SQMS, which will quickly construct and run numerous modules while creating control systems and microwave equipment to coordinate quantum information encoding and analysis devices. Due to their lower gate count and circuit depth, qudits can aid sophisticated algorithms. Multilevel qudits describe the underlying physics better than qubits for many simulation challenges in high energy physics (HEP) and other fields, simplifying simulation operations.

High-Energy Physics to Quantum Communication

SQMS advancements affect several scientific and technological fields, including:

High Energy Physics (HEP): Centre specialists predict SQMS quantum technologies will boost present detection sensitivities by orders of magnitude, which could help identify dark matter and unknown particles. Lattice-gauge theory and neutrino oscillations are being studied on quantum computing platforms in addition to experimental applications like jet and track reconstruction during high-energy particle collisions, rare signal extraction, and exotic physics outside the Standard Model.

Quantum Communication: Researchers will use microwave photon-coherence devices with seconds of coherence. Long-range quantum communication systems require quantum memory, which this feature enables. SQMS researchers also want to show microwave-to-microwave entangled state transfer between 3D quantum systems. These cavities can also serve as low-loss conduits and “adapters” to link QPUs in different refrigerators, enabling superconducting quantum computers to develop into larger quantum data centres.

Collaboration through “Co-Design”

SQMS's success, which brought together “materials science experts, quantum device and quantum computing researchers, and high energy physics experts” from DOE laboratories, industry, academia, and other federal entities like NIST, shows its extensive collaboration. “Sustained alignment of scientific goals with technological implementation” is guaranteed by “co-design”.

The SQMS Centre's superconducting qubit performance is being improved by a nanofabrication taskforce led by NIST experts from the PML and CTL. They invented encasing niobium-based qubits in tantalum or gold to reduce material losses and improve coherence.

While sapphire substrates and other material interfaces limit qubit coherence times to 1 millisecond, this taskforce has developed qubits with coherence times of up to 0.6 milliseconds for their best-performing qubits, advancing superconducting quantum technology.