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About Quantum Computer

patterns to the number of qubits by using the quantum superposition of quantum mechanics. For example, the number of expressible combinations surpasses the number of atoms in the entire universe when it comes to a quantum computer with 300 qubits.

Quantum computers can explore astronomical number of combinations possibilities comprehensively.

Power

A quantum computer is a calculator that can process a large number of combinations at once, but measurement of quantum state will lead to a single combination of computation. Therefore, it is necessary to wisely design a quantum algorithm that retrieves desired results with a high probability. Without a proper quantum algorithm, a quantum computer measuring the superposed state with 300 qubits will only be a machine that chooses one random atom from all atoms in the universe. 

The most famous quantum algorithm is Shor’s factoring algorithm that enables exponential speedup of factoring. This breaks the RSA, a encryption method that is ubiquitously used today.

Industrial applications

Not all computations done with supercomputers get faster with quantum computers. It is important to find problems that can be computed faster than traditional computers using a quantum algorithm.

Industrial useful applications of quantum computers known include the following:
・Advancement of material discovery by calculating exact chemical energies.
・Speedup of calculations (ex. option price) done by financial engineering
・Acceleration of fluid calculation by speeding up inverse matrix calculation
・Speedup in search in unorganized databases

However, these applications will not be realized in the near future. The function of error correction is needed for suppressing the noise of calculation. The appearance of such device is considered to be 20 to 50 years from now.

Quantum computers in recent years

The target of development in these years is the NISQ (Noisy Intermediate Scale Quantum) device, a quantum computer that has no error correction. Performance of these computers are limited compared to the ones with error correction.

However, research and development using NISQ device has become popular in recent years, and a number of theories that realize industrial and social applications are being proposed.

NISQ devices will work well with simulating quantum mechanical behavior and handling high dimensional data. Therefore, its contribution is expected to bring the discovery of new materials and medicines by quantum chemistry calculation and speedup of machine learning and optimization, and is worked on all over the world.

For details about quantum computers, please see Qmedia (Japanese) run by QunaSys.