Impact of Long-Lived Qubits on Quantum Computing

Major milestone achieved in new quantum computing architecture "A team led by the U.S. Department of Energy (DOE)’s Argonne National Laboratory has achieved a major milestone toward future quantum computing. They have extended the coherence time for their novel type of qubit to an impressive 0.1 milliseconds — nearly a thousand times better than the previous record." "The team’s qubit is a single electron trapped on an ultraclean solid-neon surface in a vacuum. The neon is important because it resists disturbance from the surrounding environment. Neon is one of a handful of elements that do not react with other elements. The neon platform keeps the electron qubit protected and inherently guarantees a long coherence time." "Yet another important attribute of a qubit is its scalability to link with many other qubits. The team achieved a significant milestone by showing that two-electron qubits can couple to the same superconducting circuit such that information can be transferred between them through the circuit. This marks a pivotal stride toward two-qubit entanglement, a critical aspect of quantum computing." "The team has not yet fully optimized their electron qubit and will continue to work on extending the coherence time even further as well as entangling two or more qubits." This research was published in Nature Physics (https://lnkd.in/d5Y5Dfea) https://lnkd.in/dkXd_Uje

“But in a new study, published May 7 in the journal Nature Communications Materials, researchers proposed using a new, pure form of silicon — the semiconductor material used in conventional computers — as the basis for a qubit that is far more scalable than existing technologies. Building qubits from semiconducting materials like silicon, gallium or germanium has advantages over superconducting metal qubits, according to the quantum computing company QuEra. The coherence times are relatively long, they are cheap to make, they operate at higher temperatures and they are extremely tiny — meaning a single chip can hold huge numbers of qubits. But impurities in semiconducting materials cause decoherence during computations, which makes them unreliable. In the new study, the scientists proposed making a qubit out of silicon-28 (Si-28), which they described as the "world's purest silicon," after stripping away the impurities found in natural silicon. These silicon-based qubits would be less prone to failure, they said, and could be fabricated to the size of a pinhead. Natural silicon is normally made up of three isotopes, or atoms of different masses — Si-28, Si-29 and Si-30. Natural silicon works well in conventional computing due to its metalloid properties, but problems arise when using it in quantum computing. Si-29 in particular, which makes up 5% of natural silicon, causes a "nuclear flip-flopping effect" that leads to decoherence and the loss of information. In the study, the scientists got around this by developing a new method to engineer silicon without Si-29 and Si-30 atoms. "Now that we can produce extremely pure silicon-28, our next step will be to demonstrate that we can sustain quantum coherence for many qubits simultaneously," project co-supervisor David Jamieson, professor of physics at the University of Melbourne, said in the statement. "A reliable quantum computer with just 30 qubits would exceed the power of today's supercomputers for some applications." https://lnkd.in/gAUmAcdd

One of the original motivations for considering spins in silicon for quantum computing was experiments from the 1960’s showing incredible spin lifetimes event at 2 Kelvin and above. That’s “hot” for solid-state qubits which usually operate at dilution refrigerator temperatures, or ~50-100 milli-Kelvin. In the last few years several groups have shown that even two-qubit gate operations — which are typically much more sensitive to noise sources — can operate at elevated temperatures, at least up to ~99% fidelity levels. We wanted to start looking at what the fundamental limits to two-qubit gate performance in spin qubits may be as a function of temperature. The paper just published below is just a first step, but our results show that at least for phonon-caused infidelities on the exchange interaction there are still more “nines” of fidelity that should be achievable. https://lnkd.in/eySQdRkv