Enlarge / The quantum network is a bit bulkier than Ethernet. (credit: ETH Zurich / Daniel Winkler )

A new experiment uses superconducting qubits to demonstrate that quantum mechanics violates what's called local realism by allowing two objects to behave as a single quantum system no matter how large the separation between them. The experiment wasn't the first to show that local realism isn't how the Universe works—it's not even the first to do so with qubits.

But it's the first to separate the qubits by enough distance to ensure that light isn't fast enough to travel between them while measurements are made. And it did so by cooling a 30-meter-long aluminum wire to just a few microKelvin. Because the qubits are so easy to control, the experiment provides a new precision to these sorts of measurements. And the hardware setup may be essential for future quantum computing efforts.

Getting real about realism

Albert Einstein was famously uneasy with some of the consequences of quantum entanglement. If quantum mechanics were right, then a pair of entangled objects would behave as a single quantum system no matter how far apart the objects were. Altering the state of one of them should instantly alter the state of the second, with the change seemingly occurring faster than light could possibly travel between the two objects. This, Einstein argued, almost certainly had to be wrong.

Enlarge / The D-Wave hardware is, quite literally, a black box. (credit: D-Wave)

Before we had developed the first qubit, theoreticians had done the work that showed that a sufficiently powerful gate-based quantum computer would be able to perform calculations that could not realistically be done on traditional computing hardware. All that is needed is to build hardware capable of implementing the theorists' work.

The situation was essentially reversed when it came to quantum annealing . D-Wave started building hardware that could perform quantum annealing without a strong theoretical understanding of how its performance would compare to standard computing hardware. And, for practical calculations, the hardware has sometimes been outperformed by more traditional algorithms.

On Wednesday, however, a team of researchers, some at D-Wave, others at academic institutions, is releasing a paper comparing its quantum annealer with different methods of simulating its behavior. The results show that actual hardware has a clear advantage over simulations, though there are two caveats: errors start to cause the hardware to deviate from ideal performance, and it's not clear how well this performance edge translates to practical calculations.

Enlarge / Two generations of Google's Sycamore processor. (credit: Google Quantum AI)

Today, Google announced a demonstration of quantum error correction on its next generation of quantum processors, Sycamore. The iteration on Sycamore isn't dramatic—it's the same number of qubits, just with better performance. And getting quantum error correction isn't really the news—they'd managed to get it to work a couple of years ago.

Instead, the signs of progress are a bit more subtle. In earlier generations of processors, qubits were error-prone enough that adding more of them to an error-correction scheme caused problems that were larger than the gain in corrections. In this new iteration, adding more qubits and getting the error rate to go down is possible.

We can fix that

The functional unit of a quantum processor is a qubit, which is anything—an atom, an electron, a hunk of superconducting electronics—that can be used to store and manipulate a quantum state. The more qubits you have, the more capable the machine is. By the time you have access to several hundred, it's thought that you can perform calculations that would be difficult to impossible to do on traditional computer hardware.

Enlarge (credit: QuEra)

Quantum computing has entered a bit of an awkward period. There have been clear demonstrations that we can successfully run quantum algorithms, but the qubit counts and error rates of existing hardware mean that we can't solve any commercially useful problems at the moment. So, while many companies are interested in quantum computing and have developed software for existing hardware (and have paid for access to that hardware), the efforts have been focused on preparation. They want the expertise and capability needed to develop useful software once the computers are ready to run it.

For the moment, that leaves them waiting for hardware companies to produce sufficiently robust machines—machines that don't currently have a clear delivery date. It could be years; it could be decades. Beyond learning how to develop quantum computing software, there's nothing obvious to do with the hardware in the meantime.

But a company called QuEra may have found a way to do something that's not as obvious. The technology it is developing could ultimately provide a route to quantum computing. But until then, it's possible to solve a class of mathematical problems on the same hardware, and any improvements to that hardware will benefit both types of computation. And in a new paper, the company's researchers have expanded the types of computations that can be run on their machine.

Enlarge / According to Werner Heisenberg and Niels Bohr, when it comes to the subatomic world, we’re just goldfish. (credit: Aurich Lawson | Getty Images)

Quantum mechanics is simultaneously beautiful and frustrating.

Its explanatory power is unmatched. Armed with the machinery of quantum theory, we have unlocked the secrets of atomic power, divined the inner workings of chemistry, built sophisticated electronics, discovered the power of entanglement, and so much more. According to some estimates, roughly a quarter of our world’s GDP relies on quantum mechanics.

Yet despite its overwhelming success as a framework for understanding what nature does, quantum mechanics tells us very little about how nature works. Quantum mechanics provides a powerful set of tools for successfully making predictions about what subatomic particles will do, but the theory itself is relatively silent about how those subatomic particles actually go about their lives.

Enlarge / Tracking acceleration using matter waves hasn't previously been implemented in a portable form. (credit: J. Burrus/NIST )

A team of researchers from France has developed the first three-directional hybrid quantum inertial sensor, which can measure acceleration without using satellite signals. At the heart of this breakthrough device is something called "matter wave interferometry," which uses two distinct characteristics of quantum mechanics: wave-particle duality and superposition.

In the cloud

The device consists of a cloud of rubidium atoms that are cooled to temperatures nearing absolute zero. The atoms are placed in a vacuum and are in free fall due to gravity.

Once cooled, a series of three laser flashes are shone on the atoms, creating matter waves in the rubidium atoms. According to the laws of quantum mechanics, at extremely low temperatures, atoms do not behave like standard particles. They also behave as waves that can undergo diffraction and interference like light does.

Enlarge (credit: IBM )

Today, IBM announced the latest generation of its family of avian-themed quantum processors, the Osprey. With more than three times the qubit count of its previous-generation Eagle processor, Osprey is the first to offer more than 400 qubits, which indicates the company remains on track to release the first 1,000-qubit processor next year.

Despite the high qubit count, there's no need to rush out and re-encrypt all your sensitive data just yet. While the error rates of IBM's qubits have steadily improved, they've still not reached the point where all 433 qubits in Osprey can be used in a single algorithm without a very high probability of an error. For now, IBM is emphasizing that Osprey is an indication that the company can stick to its aggressive road map for quantum computing, and that the work needed to make it useful is in progress.

On the road

To understand IBM's announcement, it helps to understand the quantum computing market as a whole. There are now a lot of companies in the quantum computing market, from startups to large, established companies like IBM, Google, and Intel. They've bet on a variety of technologies, from trapped atoms to spare electrons to superconducting loops. Pretty much all of them agree that to reach quantum computing's full potential, we need to get to where qubit counts are in the tens of thousands, and error rates on each individual qubit are low enough that these can be linked together into a smaller number of error-correcting qubits.

Enlarge / The 2022 Nobel Prize in Physics goes to Alain Aspect, John F. Clauser, and Anton Zeilinger, "for experiments with entangled photons, establishing the violation of Bell inequalities and pioneering quantum information science." (credit: Niklas Elmehed/Nobel Prize Outreach)

Cornell University physicist N. David Mermin once described quantum entanglement as "the closest thing we have to magic" since it means that disturbances in one part of the universe can instantly affect distant other parts of the universe, somehow bypassing the cosmic speed-of-light limit. Albert Einstein memorably dubbed it "spooky action at a distance." Today, The Royal Swedish Academy of Sciences honored three physicists with the 2022 Nobel Prize in Physics for their work on entanglement. Alain Aspect, John F. Clauser, and Anton Zeilinger were recognized "for experiments with entangled photons, establishing the violation of Bell inequalities and pioneering quantum information science."

When subatomic particles interact, they can become invisibly connected even though they may be physically separated. So knowledge about one partner can instantly reveal knowledge about its twin. If you measure the state of one, you will know the state of the other without having to make a second measurement because the first measurement determines the properties of the other particle as well.

There are many different ways particles can become entangled, but in every case, both particles must arise from a single "mother" process. For instance, passing a single photon through a special kind of crystal can split that photon into two new "daughter" particles. We'll call them "green" and "red" (shorthand for more abstract particle properties like spin or velocity). Those particles will be entangled. Energy must be conserved, so both daughter particles have a lower frequency and energy than the original mother particle, but the total energy between them equals the mother's energy. We have no way of knowing which is the green one and which is the red. We just know that each daughter photon has a 50-50 chance of being one or the other color. But should we chance to see one of the particles and note that it is red, we can instantly conclude that the other must be green.

Enlarge (credit: Aurich Lawson / Getty Images)

Inspired by the functioning of pulsed lasers, scientists from France and Japan have developed an acoustic counterpart that enables the precise and controlled transmission of single electrons between quantum nodes.

Riding the waves

The spin of an electron can serve as a basis for creating qubits—the basic unit of information of quantum computing. In order to process or store that information, the information in qubits may have to be transported between quantum nodes in a network.

One option is transporting the electrons themselves, something that can now be done by having them ride sound waves. “More than 10 years ago, we demonstrated it for the first time,” said lead researcher Christopher Bauerle of the Grenoble-based Institute Néel .