Researchers Track ‘Lifetime’ of Graphene Qubits

This first of its kind measurement brings practical quantum computers closer to reality.
Kashyap Vyas

When graphene was first discovered in 2004, the science community went rave about how it is capable of many impressive feats, and now we are slowly starting to put graphene to use. 

Recently, researchers from the MIT and other prestigious institutions have been able to measure how long a graphene qubit stays in its incoherent state.

Too complex of a statement? We will ton things down. With the processors that we have on our computers, the semiconductors in them have two states, 1 and 0.

Information is processed by these transistors switching back and forth between the states. This type of operation may be efficient for solving or running our native apps and games, but for solving complex problems related to quantum computing, the conventional systems fall short.

Qubits: Quantum Information Transferred in Bits 

To effectively solve quantum problems, the qubits or quantum bits should remain in a state that sits between the two. This middle state is the superimposition of two extreme states.

The amount of time where these qubits can remain in the superimposition state is known as coherent time. However, this state is not stable when compared to 1 or 0.

This makes it harder for the qubits to stay in superimposition for extended periods of time.

The more coherent time a qubit can produce, the more its computing power will be. Graphene was introduced to quantum computing to make faster and efficient processors.

Traditionally, qubits were made by sandwiching an insulator between two superconducting materials. The resultant form is called a “Josephson junction.”

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When applied a current, the electrons shift from one superconductor to the other superconductor, creating varying states. This method resulted in quite a lot of energy wastage due to the heavy current requirement, so the scientists wanted to change the insulator setup, and graphene was their choice.

Graphene is a 2D sheet of carbon atoms that is just one atom thick. The introduction of the new material proposed greater gains regarding power efficiency and overall computing power.

The scientists sandwiched the graphene layer with hexagonal boron nitride (hBN), a Van Der Waals insulator. Instead of current, the graphene layer qubit uses voltage to change states, this was much more efficient and quick in processing information while delivering power savings.

However, researchers could not measure how much of difference graphene brings to the table as they lacked the equipment or method to measure the respective coherent time effectively.

Graphene Qubits: Flawed as of Now, But Possibly the Future!

That all changed when the researchers finally were able to demonstrate a graphene-based qubit in its coherent state, thanks to a change in input voltage (the same methodology used in transistors to change their state). And, the coherent time was measured to be 55 nanoseconds.

The new qubits can also increase the qubits/die count very much. With the electric current loop method, only 1000 qubits could be placed on a single chip.


With voltage controlled method, the number of qubits per die can be increased to the range of millions. The electric current loop qubits, however, have their coherent time in the range of microseconds.

This is far greater than the nanoseconds offered by graphene qubits.

The researchers are now working out on ways in which the coherent time of graphene qubits can be effectively increased to the levels of electric current loop qubits.

This way, we will have new quantum computing units that are many times faster than the ones we have today!