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Scientists from the Institute of Physics and Technology of the Russian Academy of Sciences and MIPT have let two electrons loose in a system of quantum dots to create a quantum computer memory cell of a higher dimension than a qubit (a quantum bit). In their study published in Scientific Reports, the researchers demonstrate for the first time how quantum walks of several electrons can help to implement quantum computation.

"By studying the system with two electrons, we solved the problems faced in the general case of two identical interacting particles. This paves the way toward compact high-level structures," says Leonid Fedichkin, associate professor at MIPT's Department of Theoretical Physics.

In a matter of hours, a quantum computer would be able to hack through the most popular cryptosystem used by web browsers. As far as more benevolent applications are concerned, a quantum computer would be capable of molecular modeling that accounts for all interactions between the particles involved. This in turn would enable the development of highly efficient solar cells and new drugs. To have practical applications, a quantum computer needs to incorporate hundreds or even thousands of qubits. And that is where it gets tricky.

As it turns out, the unstable nature of the connection between qubits remains the major obstacle preventing the use of quantum walks of particles for quantum computation. Unlike their classical analogs, quantum structures are extremely sensitive to external noise. To prevent a system of several qubits from losing the information stored in it, liquid nitrogen (or helium) needs to be used for cooling. Plenty of schemes have been proposed for the experimental realization of a separate qubit. In an earlier study, a research team led by Prof. Fedichkin demonstrated that a qubit could be physically implemented as a particle "taking a quantum walk" between two extremely small semiconductors known as quantum dots, which are connected by a "quantum tunnel." From the perspective of an electron, the quantum dots represent potential wells. Thus, the position of the electron can be used to encode the two basis states of the qubit—|0? and |1?—depending on whether the particle is in one well or the other. Rather than sit in one of the two wells, the electron is smeared out between the two different states, taking up a definite position only when its coordinates are measured. In other words, it is in a superposition of two states.http://phys.org/news/2016-12-scientists-quantum-memory-cell-higher.html

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