The Rise of All-Nitride Qubits for 1Kelvin Quantum Computers
New All-Nitride Qubits Enable High-Temperature, Scalable Computing All-Nitride Qubits
Quantum technology has advanced with superconducting qubits that can operate at temperatures too high for quantum processing. This finding, disclosed in recent preprints and publications, involves industrial-standard atomic layer deposition (ALD) and the “all-nitride” architecture. It may address one of the biggest challenges to developing a quantum computer: expensive, intense cooling.
Overcoming Cold Limits For decades, superconducting quantum circuits, which operate at temperatures below 100 millikelvin, have been the electronics industry's "divas." Even a small heat can affect the fragile quantum states, or “qubits,” at these frigid depths, triggering decoherence and errors. Scientists spend a lot of energy using sophisticated dilution refrigerators that employ rare Helium-3 (3He), a scarce material. New study by Danqing Wang and colleagues demonstrates that transmon qubits made of NbN and AlN trilayers may maintain microsecond-scale relaxation periods at temperatures above 300 mK. It may seem frigid, but 300 mK represents a quantum physics breakthrough. Simple cryogenic systems can reach this temperature range, eliminating the need for 3He refrigeration. ALD Revolution: Lab to Foundry Atomic Layer Deposition (ALD), which makes these qubits, is about as crucial as temperature. ALD is a valuable thin-film growth standard because it carefully controls layer thickness and composition. ALD is scalable and compatible with semiconductor foundries, unlike “lab-style” procedures like angled evaporation or metal lift-off. The researchers carefully adjusted the number of ALD cycles to establish the AlN limit to perform Josephson tunneling across barriers of varied thicknesses with critical current densities spanning seven orders of magnitude. Quantum computers could be made on 300 mm wafers like microchips due to their uniformity and versatility. CMOS-compatible transmons with coherence times above 100 μs have been demonstrated on 300 mm prototype lines in recent studies. Material Effects on Nitrides? Calculations determine whether to employ “all-nitride” materials like NbN and AlN. Metallic superconductor niobium nitride resists thermal noise due to its high transition temperature (Tc). Advanced processing is used for these materials. Researchers recently developed Atomic Layer Etching (ALE) for NbN by sequentially exposing O2 and H2/SF6 plasmas. This low-damage etching approach maintains the film's high transition temperature better than reactive ion etching, which often damages and increases microwave surface loss. However, switching to nitrides is tough. Wurtzite Aluminum Nitride is piezoelectric, hence in-plane strain can affect performance. These devices' electric fields may unintentionally trigger bulk acoustic modes, causing “parasitic coupling” and dielectric loss, study shows. For the next generation of circuit design, balancing these materials' advantages with their mechanical properties is crucial. 1 Kelvin Frontier Exam The quest for “hotter” quantum computers goes beyond 300 mK. Parallel superconducting qubit scaling to millimeter-wave (100 GHz) is underway. Higher frequencies dramatically minimize thermal noise, allowing electronics to work at 1 Kelvin. Dilution refrigerators for microwave qubits have less cooling power than liquid Helium-4 (4He) at 1 K. This “thermal budget” allows the quantum array to be directly integrated with the computer's classical control circuits, or “wires and switches”. The “wiring nightmare” caused by most quantum systems' need to maintain their enormous control hardware at ambient temperature occurs when systems reach millions of qubits for error correction. The Future: Coherence and Scale Despite the promising all-nitride ALD qubits, scientists are still working to match other materials' record-breaking lifetimes. Recent tantalum qubits have lives over 0.3 ms. Separating loss sources like “two-level systems” (TLS) on circuit surfaces and interfaces is necessary to accomplish these record timings. ALD-based NbN qubits' success suggests prioritizing high-temperature operation and industrial scalability. Millimeter-wave designs and current manufacturing methods like ALD and ALE are helping the quantum industry move from unique laboratory research to a CMOS-compatible quantum processor. These methods may eliminate ultra-deep-freeze cooling, enabling more powerful, widespread, and simpler quantum sensors and computers.