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Technical Perspective: Deciphering Errors to Reduce the Cost of Quantum Computation

By Daniel Gottesman

Communications of the ACM, Vol. 64 No. 1, Page 105
10.1145/3434157



Quantum computers may one day upend cryptography, help design new materials and drugs, and accelerate many other computational tasks. A quantum computer's memory is a quantum system, capable of being in a superposition of many different bit strings at once. It can take advantage of quantum interference to run uniquely quantum algorithms which can solve some (but not all) computational problems much faster than a regular classical computer. Experimental efforts to build a quantum computer have taken enormous strides forward in the last decade, leading to today's devices with over 50 quantum bits ("qubits"). Governments and large technology companies such as Google, IBM, and Microsoft, as well as a slew of start-ups, have begun pouring money into the field hoping to be the first with a useful quantum computer.

However, many hurdles remain before we have large-scale quantum computers capable of the tasks described here. Whereas hardware errors are rare in classical computers, they will be a significant complication for quantum computers, in part because quantum systems are small and therefore fragile, and in part because the act of observing a quantum system collapses it, destroying the superpositions that distinguish quantum from classical. Even a single atom passing by can interact with a qubit, develop a correlation with it, and thereby eliminate the qubit's quantum coherence.

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