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Diamonds as quantum memory

In contrast to conventional devices, which store figures with the value of zero or one, quicker and scalable quantum computers can realize both zero and one at the same time in the form of quantum bits. These enable quantum mechanical computers to calculate many different figures simultaneously and thus yield the desired results much more quickly. One of the largest quantum computers in use at the present time is being operated in Innsbruck. It uses captured ions to store the quantum information, and can carry out calculations with up to 14 quantum bits.

The heart of a computer is the processors and the main memory. People have long been searching for building blocks which can assume these functions in a future quantum computer. Viennese researchers have now demonstrated that diamonds are suitable for use as quantum memory, and can transmit the information to be stored with the help of microwaves.

Conventional information technology uses the bit as the smallest unit of information, which can capture two situations – yes/no or 0/1. In a quantum computer the quantum states are to serve as the smallest unit of information, otherwise known as quantum bits (Qubits). In this case the laws of the quantum world apply. Thus such a quantum state can reflect the state of uncertainty between two possibilities i.e. not only the values of 0 and 1 but all values in between. Such quantum bits enable much quicker solutions to be developed for certain problems than with a typical computer.

In such cases the processor carrie s out the calculations, and the results will be transmitted via a so-called data bus to the main memory, where the results are to be stored as permanently as possible. A variety of ideas applying to processors and memory are being pursued in the efforts to create the quantum computer. “However, there is still no quantum system which can fulfill all requirements at the same time“, says Johannes Majer from the Institute of Atomic and Subatomic Physics at the Vienna University of Technology. For this reason Viennese researchers have linked two different quantum systems – microwaves and diamonds – in order to exploit their advantages. 

Microwaves as a data bus

According to the author Robert Amsüss, the objective of the study is to generate a quantum state with the help of a superconducting circuit. Such a circuit implemented on a chip can be manipulated like an artificial atom Thus it can, for example, transmit the desire quantum state in the form of a photon with a wave length in the microwave range. In the recently published study carried out at the "Vienna Center for Quantum Science and Technology" (VCQ), the scientists have theoretically demonstrated that a microwave resonator which absorbs the incoming microwaves can be linked to a think diamond layer. As a result, the microwave resonator acts as a data bus in a conventional PC, which further transmits the information to the memory i.e. the diamond. The diamonds used here may not be perfect, and the crystal may not only consist of carbon atoms. On the contrary, foreign atoms, more specifically nitrogen, as well as spaces must be built i nto the crystal grid. The quantum information can be stored in the nitrogen atoms. The next step for the scientists is to generate quantum bits with the help of superconducting circuits and store the information in the diamond.

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