The atom: nature’s qubit

The most important part of any quantum computer are its quantum bits, or qubits. IonQ’s qubits are ionized ytterbium atoms, a silvery rare-earth metal. Each ytterbium atom is perfectly identical to every other ytterbium atom in the universe.

Moreover, once prepared in a particular stable quantum state, they can remain in that state for very long periods of time — they're so consistent they're used in one of the most accurate atomic clocks ever built.

Trapping an ion

Once we've turned our atom into an ion, we use a specialized chip called a linear ion trap to hold it precisely in 3D space. This small trap features around 100 tiny electrodes precisely designed, lithographed, and controlled to produce electromagnetic forces that hold our ions in place, isolated from the environment to minimize environmental noise and decoherence.

One qubit, or one hundred

We don’t stop at one ion; that wouldn’t make a very useful quantum processor. We can (and do!) load any number of ions into a linear chain.

This on-demand reconfigurability allows us to theoretically create anything from a one-qubit system to a 100+ qubit system without having to fabricate a new chip or change the underlying hardware. To date, we’ve run single-qubit gates on a 79 ion chain, and complex algorithms on chains of up to 35+ ions.

Getting ready to compute

Before we can use our ions to perform quantum computations, we have to prepare them for the task. This has two major steps: cooling, which reduces computational noise and makes our ions better qubits, followed by state preparation, which initializes each ion into a well-defined “zero” state, ready to perform algorithms.

Computing with atoms

We compute using a series of operations called gates to manipulate the qubits’ state, first encoding and then operating on the information we want to calculate.

To perform these gates, we use an array of individual laser beams, each imaged onto an individual ion, plus one “global” beam. The interference between the two beams produces a beat note that is at exactly the necessary energy to kick the qubits into a different state.

Reading the answer

Once the computation has been performed, reading the answer from the ions is done by shining a resonant laser on all of them at the same time. This process collapses any complex quantum information we’ve created and forces each qubit into one of two states.

Collecting and measuring this light allows us to simultaneously read the collapsed state of every ion — one of the states glows in response to the laser light, the other does not. We interpret this as a binary string, where each glowing atom is a one, and each dark atom is a zero.

Isolating the ions

To successfully hold complex quantum information, qubits can't interact with anything. A single stray hydrogen atom colliding with an ion can spoil the whole thing, collapsing delicate states, making ions switch places, or knocking the chain out of the trap entirely.

So, we put the trap inside an ultra-high vacuum chamber, pumped down to around 10^-11 Torr. At this pressure, there are about one hundred trillion times fewer molecules per cubic inch than the air you're currently breathing.

Putting it all together

Once everything's in the chamber, the whole assembly goes in an even larger enclosure with a variety of electrical, mechanical, and optical control systems.

Then, it all gets hooked to a classical computer running our custom control software, and after a great deal of calibration, it's a fully functioning quantum computer, ready to perform gates and run algorithms with world-leading fidelity.