Here’s an interesting article that just showed up in Popular Mechanics which could have an enormous impact on the future of quantum computing, among many other things:
In new research, scientists from Aalto University in Finland say they’ve skirted the Heisenberg Uncertainty Principle that underpins—or undermines—every experiment in quantum mechanics. The secret is an instrument called a bolometer, and using it could help scientists who continue to work on qubit-based quantum computers.
One of the fundamental properties of quantum mechanics is bound up in the Heisenberg Uncertainty Principle, which in its purest form simply states that at the quantum level of atoms and their components, linked characteristics within a quantum system (e.g. position and momentum) can never be known beyond a certain of level of precision, related to Planck's Constant — e.g. the more precisely we can measure a particle’s position, the less precise our knowledge of its momentum will be, and vice-versa. And this brings us to one of the fundamental problems in the emerging field of quantum computing:
On the particle level, the unit of quantum computing is the qubit. It mimics the traditional electricity-based on/off switch of our computer bits, but shows quantum behaviors like superposition. Measuring traditional computing is simple, because electricity through semiconductors, resistors, and conductive wires is quite subdued. In other words, there's less noise—what you’re measuring isn’t moving around and making your data less reliable and consistent.
Measuring the performance of qubits, on the other hand, is difficult even when pursued in the simplest ways. That’s because of the Heisenberg Uncertainty Principle, which tells us that observing a quantum system inherently makes it behave differently. In this case, that new behavior creates noise.
Reducing noise is a major project in quantum computing—largely because, so far, these systems rely heavily on abstract and theoretical discussions in lieu of measurements that scientists can compare to one another. Even the amount of noise is hard to predict. So, to combat it, researchers have tried different things, like “squeezing” the noise all the way into one variable so the other stays more true, using a parametric amplifier.
In their new peer-reviewed paper in Nature Electronics, the researchers from Aalto University explain the limits of that approach. “Parametric amplifiers,” they wrote, “can offer high gain and low noise, but introduce challenges in terms of scaling to large numbers of qubits.” And these amplifiers still perpetuate the noise from the Heisenberg Uncertainty Principle itself, which has been considered an immovable object in the fight against noise—until this team decided to try a bolometer.
For those who have not encountered this type of device before, a bolometer simply measures radiant heat by means of a material having a temperature-dependent electrical resistance first invented in 1878 by the American astronomer Samuel Pierpont Langley. The Aalto team updated the original concept by using superconducting materials that are cooled to near absolute zero so even the most minute temperature changes can be detected. These nanobolometers
“have been shown to be fast and sensitive enough for the readout of superconducting qubits, reaching thermal time constants in the range of hundreds of nanoseconds and energy resolution of a few typical microwave photons,” the researchers explain in their paper. And because nanobolometers both aren’t amplifying anything and are operating in a vacuum, they avoid added Heisenberg noise altogether.
By tuning them carefully, the researchers reduced noise until their measurements were as noiseless as possible. This process works for systems with many qubits, which is essential as quantum computers “scale up” from literally a handful to enough to constitute a usable computer.
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“For example, we can swap the bolometer material from metal to graphene, which has a lower heat capacity and can detect very small changes in its energy quickly,” researcher András Gunyhó said in a statement. “And by removing other unnecessary components, we can achieve a smaller and simpler measurement device that makes scaling-up to higher qubit counts more feasible.”
Gunyhó says the right advanced materials could jump from this team’s 92.7 percent fidelity measurement to 99.9 percent—arguably once a pipe dream, but maybe within our reach at last.
This would be the Holy Grail of quantum computing — true coherence between qubits!