# Physicists have calculated the time of the state of superposition of graphene qubits

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2019-01-02 23:45:11

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The Possibility of practical use of quantum computers one step closer thanks to graphene. Experts from the Massachusetts Institute of technology and their colleagues from other research institutions were able to calculate the time of superposition, which may include qubits, built on the basis of graphene. The results of the study according to article Nature Nanotechnology.

The Idea of quantum superposition is well illustrated by the famous thought experiment called "Schrodinger's cat". Imagine a box in which we placed a live cat, the atom that emits radiation with a certain probability and a device that produces a deadly gas when it detects radiation. Close the box on the half hour. Question: cat in the box alive or dead? If the probability that the gas is produced every hour, the chances that the cat in the box alive or dead is 50 to 50. In other words, the cat exists in a superposition of being both "half dead" and "half alive". To confirm current status you must open the box and see, but at the same time that we destroy a state of superposition.

Quantum computers use the same principle of superposition. Traditional computers store and process information in bits employed in the binary system of measurement of information – data are the state of "zeros" or "ones" that are understood by the computer in the form of certain teams. In the quantum computers are used, there is not half-dead and half-dead cats, qubits — the basic unit of information that can acquire simultaneous state of "zeros" and "units". This feature allows them to substantially exceed the computational ability of ordinary computers. The longer that the qubits can remain in this state (also known as coherence time), the more productive will be the quantum computer.

Scientists did not know the coherence time of qubits based on graphene, therefore, in the new study, they decided to calculate and to verify whether these qubits to be in superposition. As it turned out, I can. According to calculations, the time of the superposition of graphene qubits is 55 nanoseconds. After this they returned to their "habitual" as "zero".

"In this study, we were motivated motivation is the possibility of using properties of graphene to improve the performance of superconducting qubits. We first showed that the graphene consisting of a superconducting qubit may temporarily make the condition of quantum coherence, which is a key condition for building more complex quantum circuits. We have created a device that made it possible to measure the coherence time of the graphene qubit (the primary metric of the qubit) and find out what time a superposition of these qubits is of sufficient duration, allowing a person to manage this condition," — comments on the work of lead author of the study Joel I-Jan Wang.

It Might seem that the coherence time of 55 nanoseconds for a qubit is not so much. And you can't go wrong. It's actually a little bit, especially considering that the qubits created on the basis of other materials, showed coherence time, hundreds of times greater than this figure, indirectly indicating that quantum computers they have higher performance. However, graphene qubits have their advantages over other types of qubits, the researchers note.

For Example, graphene has a very strange but useful feature – it is able to acquire properties of superconductivity, "copying" it from the neighboring superconducting materials. Scientists from mit have tested this property by placing a thin sheet of graphene between two layers of boron nitride. The location of the graphene between two layers of superconducting material has shown that graphene a qubit can switch between States when exposed to energy, not the magnetic field, as is the case in qubits from other materials.

The Advantage of this scheme is that the qubit in this case begins to act more like a traditional transistor, opening the possibility of combining a larger number of qubits on a single chip. If we talk about qubits based on other materials, they work when you use the magnetic field. In this case, the chip would have to integrate the current loop, which in turn would occupy additional space on the chip, and also prevented the next of qubits that would result in errors in calculations. The scientists added that the use of graphene qubits more efficient because the two outer layers of boron nitride acting as a protective shell, protecting the graphene from defects through which might leak running down the chain electrons. Both of these characteristics can really help in creating practical quantum computers.

A Small coherence time of qubits graphene scientists are not scary. The researchers note that can solve this issue by changing the structure of the graphene qubit. In addition, specialists are going to understand in more details how using these qubits are moved electrons.

To Discuss the approaching era of quantum computing .

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