This New Quantum Computer Takes Advantage of a Loophole in Causality

Sending pulses in the "wrong" order could change the future of quantum computing.

3. 19. 16 by Sarah Marquart
Image by MuonRay

Levels of Energy

Quantum computers are able to try a multitude of solutions to a problem simultaneously by taking advantage of entanglement.

The pairs of entangled atoms make up “qubits”— the quantum analogs of computer bits. During a calculation, the qubits use every combination of ones and zeroes that an equivalent number of bits could hold. They explore all options and settle on the best one. Atoms have discrete energies, so a qubit with low energy would be called a 0, and one a level up would be a 1.

Researchers in Finland have figured out a way to make quantum computers more powerful by asking, “why stop here?” This is where “qutrits” come in—allowing computers three options: 0, 1, and 2, or three levels of energy.

The research team, led by Sorin Paraoanu from Aalto University, made qutrits by shooting two pulses of light at entangled atoms. Each pulse took them to a higher energy level, allowing the atoms to access all three of the energies.


Out of Order

If the atoms sat at the middle energy for too long, they could become disentangled. To combat this, Paraoanu’s team sent the pulses in the wrong order. First came the pulse to bring the atoms from 1 to 2, then the one to take them from 0 to 1.

If this doesn’t make sense to you, you’re not alone. It doesn’t make sense.

But the atoms don’t care.

Instead, when the pulse hits them, they start seeking out all of the possible energies they could go to. After the second pulse hits, they settle on the best course, even though they couldn’t have known the second was on its way when the first one came. They skipped sitting at 1 for any time at all and went right on to 2, where they were much more stable. Once they were at 2, computations could begin.


All of this activity occurs on such a small scale, but these processes are going to define the future of quantum computing, one number at a time.

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