Posted in: Quantum Computing

What’s in a qubit?

Would a carrier of information, by any other physical phenomenon, be as powerful?

A mechanical qubit

A mechanical qubit

Over the last few months, we’ve shared some videos from members of our research team explaining key concepts in quantum computing. We told you about superposition, entanglement, and quantum algorithms. And we took you behind the scenes and into our lab, in our how it works article, to see what happens when you run experiments on the Q experience. We explained why we’re excited about our 16-qubit device that’s free in beta, and told you how we benchmark quantum systems to tell how good they really are.

But… we didn’t yet take you deep into the heart of qubits themselves and explain why and how they work. Today’s blog is here to remedy that!

First, it helps to visualize a qubit. IBM researcher Muir Kumph has a great way to do that using a mechanical gyroscope he designed, which was built by our machine shop. Using this “mechanical qubit,” we have a visual analogy about how things work in the quantum world, using something we can see and touch in our classical world. It’s also super fun to play with! So, next time we’re at a public event, like this past May’s Maker Faire in San Mateo, you’re invited to “give it a spin” (pun intended!)

Once you’ve got that covered, and you decide you’re ready to roll up your sleeves and learn how to make a physical qubit, you have to decide on the kind of qubit: trapped ion, superconducting, quantum dots, etc.* IBM researcher Markus Brink recorded a quick overview of different ways that teams around the world have conceived of, and built, different types of qubits, and in particular what our approach is at IBM. He describes the key pieces of tech that go into the qubits you get to experiment with through the Q experience, which are made up of superconducting Josephson Junctions, capacitors, coupling resonators, and readout resonators.

Finally, having chosen a physical system you want to use; now how do you actually use it as a qubit? Dr. Maika Takita talks you through how we separate out the two lowest energy levels of the qubit so that we can use them as our quantum states |0〉 and |1〉, and how we can communicate with and control them. We use external controls, like microwave pulses, to change the states of the qubits (e.g. with quantum gates), entangle them, and then read their states, allowing us to actually implement quantum algorithms. You can check out some examples of quantum algorithms in our Full User Guide to the quantum experience, or go deeper into chemistry and optimization examples on our SDK.

If he were alive today, the great bard William Shakespeare might have said: “What is in a qubit? That which carries information, by any physical phenomenon, would be just as powerful.” But he’d be wrong! Qubits are unique in the way we can actually manipulate and measure their quantum mechanical properties, and this ability is truly what gives rise to the tremendous potential offered by quantum computing.

* – A research lab is also required.

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Talia Gershon, research staff member

Talia Gershon

Research Staff Member, IBM Research