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Quantum Computing Seeks Supremacy

September 22, 2020

Author: Linley Gwennap

Over the past year, quantum computing has gained momentum. Most famously, Google claimed it achieved “quantum supremacy” by programming its 53-qubit processor to perform a task that would be impossible to perform on a classical computer. Intel has demonstrated “hot qubits” and very cold control logic. IBM has increased the reliability and coherence of its qubits enough to attract more than 100 paying customers for its quantum cloud service, with many others using its free service.

Despite these advances, current quantum systems are too small and error prone to perform useful computation. Google’s quantum-supremacy algorithm has no practical value and was contrived to run quickly on its quantum chip and slowly on a classical computer. Although many researchers hope to use these computers for quantum chemistry, the most complex molecule Google has been able to model consists of 12 hydrogen atoms. (Hydrogen is the simplest of all atoms.)

These companies are exploring different methods of building quantum computers. Google and IBM, among others, focus on transmon qubits, while Intel and Microsoft are working with spin qubits. Intel has created a control chip that operates inside the dilution refrigerator, which chills the system to nearly absolute zero, whereas Microsoft placed its control chip right next to the qubits to minimize wiring. These and other innovations advance quantum computing toward commercial deployment.

A critical challenge facing quantum researchers is building reliable qubits. Holding only a tiny bit of energy—about as much as a single photon—qubits are fragile and easily disrupted by heat, radio-frequency noise, crosstalk, and other factors. Although current chips can operate for only a few microseconds, the accumulated errors turn the data into mush long before reaching that limit. Researchers have identified quantum circuits for error correction, but the circuits often require orders-of-magnitude more qubits.

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