qubit

12 Articles

Microsoft (Again) Claims Topological Quantum Computing With Majorana Zero Mode Anyons

February 20, 2025 by 5 Comments

As the fundamental flaw of today’s quantum computers, improving qubit stability remains the focus of much research in this field. One such stability attempt involves so-called topological quantum computing with the use of anyons, which are two-dimensional quasiparticles. Such an approach has been claimed by Microsoft in a recent paper in Nature. This comes a few years after an earlier claim by Microsoft for much the same feat, which was found to be based on faulty science and hence retracted.

The claimed creation of anyons here involves Majorana fermions, which differ from the much more typical Dirac fermions. These Majorana fermions are bound with other such fermions as a Majorana zero mode (MZM), forming anyons that are intertwined (braided) to form what are in effect logic gates. In the Nature paper the Microsoft researchers demonstrate a superconducting indium-arsenide (InAs) nanowire-based device featuring a read-out circuit  (quantum dot interferometer) with the capacitance of one of the quantum dots said to vary in a way that suggests that the nanowire device-under-test demonstrates the presence of MZMs at either end of the wire.

Microsoft has a dedicated website to their quantum computing efforts, though it remains essential to stress that this is not a confirmation until their research is replicated by independent researchers. If confirmed, MZMs could provide a way to create more reliable quantum computing circuitry that does not have to lean so heavily on error correction to get any usable output. Other, competing efforts here include such things as hybrid mechanical qubits and antimony-based qubits that should be more stable owing to their eight spin configurations.

Using Antimony To Make Qubits More Stable

February 16, 2025 by 6 Comments

One of the problems with quantum bits, or “qubits”, is that they tend to be rather fragile, with a high sensitivity to external influences. Much of this is due to the atoms used for qubits having two distinct spin states of up or down, along with the superposition. Any disturbing of the qubit’s state can cause it to flip between either spin, erasing the original state. Now antimony is suggested as a better qubit atom by researchers at the University of New South Wales in Australia due to it having effectively eight spin states, as also detailed in the university press release along with a very tortured ‘cats have nine lives’ analogy.

For the experiment, also published in Nature Physics, the researchers doped a silicon semiconductor with a single antimony atom, proving that such an antimony qubit device can be manufactured, with the process scalable to arrays of such qubits. For the constructed device, the spin state is controlled via a transistor constructed on top of the trapped atom. As a next step a device with closely spaced antimony atoms will be produced, which should enable these to cooperate as qubits and perform calculations.

By having the qubit go through many more states to fully flip, these qubits can potentially be much more stable than contemporary qubits. That said, there’s still a lot more research and development to be done before a quantum processor based this technology can go toe-to-toe with a Commodore 64 to show off the Quantum Processor Advantage. Very likely we’ll be seeing more of IBM’s hybrid classical-quantum systems before that.

Experimental sequence for the Ramsey-type phonon anharmonicity measurement. (Credit: Yu Yang et al., Science, 2024)

Creating A Mechanical Qubit That Lasts Longer Than Other Qubits

December 27, 2024 by No comments

Among the current challenges with creating quantum computers is that the timespan that a singular qubit remains coherent is quite limited, restricting their usefulness. Usually such qubits consist of an electromagnetic resonator (boson), which have the advantage of possessing discrete energy states that lend themselves well to the anharmonicity required for qubits. Using mechanical resonators would be beneficial due to the generally slower decoherence rate, but these have oscillations (phonons) that are harmonic in nature. Now researchers may have found a way to use both electromagnetic qubits and mechanical resonators to create a hybrid form that acts like a mechanical qubit, with quite long (200 µs) coherence time.

As per the research paper by [Yu Yang] and colleagues in Science (open access preprint), their experimental mechanical qubit (piezoelectric disc and superconducting qubit on sapphire) was able to be initialized and read out, with single-qubit gates demonstrated. The experimental sequence for the phonon anharmonicity measurement is shown in the above image (figure 2 in the paper), including the iSWAP operations which initialize the hybrid qubit. Effectively this demonstrates the viability of such a hybrid, mechanical qubit, even if this experimental version is not impressive yet compared to the best electromagnetic qubit. Those have managed to hit a coherence time of 1 ms.

The lead researcher, [Yu Yang] expresses his confidence that they can improve this coherence time with more optimized designs and materials, with future experiments likely to involve more complex quantum gates as well as sensor designs.

Intel To Ship Quantum Chip

June 17, 2023 by 29 Comments

In a world of 32-bit and 64-bit processors, it might surprise you to learn that Intel is releasing a 12-bit chip. Oh, wait, we mean 12-qubit. That makes more sense. Code named Tunnel Falls, the chip uses tiny silicon spin quantum bits, which Intel says are more advantageous than other schemes for encoding qubits. There’s a video about the device below.

It is a “research chip” and will be available to universities that might not be able to produce their own hardware. You probably aren’t going to find them listed on your favorite online reseller. Besides, the chip isn’t going to be usable on a breadboard. It is still going to take a lot of support to get it running.

Intel claims the silicon qubit technology is a million times smaller than other qubit types. The size is on the order of a device transistor — 50 nanometers square — simplifying things and allowing denser devices. In silicon spin qubits, information resides in the up or down spin of a single electron.

Of course, even Intel isn’t suggesting that 12 qubits are enough for a game-changing quantum computer, but you do have to start somewhere. This chip may enable more researchers to test the technology and will undoubtedly help Intel accelerate its research to the next step.

There is a lot of talk that silicon is the way to go for scalable quantum computing. It makes you wonder if there’s anything silicon can’t do? You can access today’s limited quantum computers in the proverbial cloud.

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MIT Spins Qubits Round And Round

February 16, 2023 by 2 Comments

Quantum computers are coming, but there are still many problems with realizing practical machines. One is finding a reliable and affordable way to encode qubits — the basic unit for quantum computers. MIT researchers have a proposal. By using two slightly different colored lasers, they can manipulate nuclear spin. This isn’t the first time someone’s tried to use light to impact spin, but according to MIT, the other methods use an indirect coupling which is more prone to noise, something that limits the viability of quantum computers. They published a recent paper on the process if you want to read more.

Nuclear spin has weak interactions, but the new method doesn’t require intermediate steps, so it may be much more practical than previous methods. MIT mentions that typical quantum elements have coherence time limits, which means data stored in them becomes useless in less than a second. The new method promises to have coherence times measured in hours.

The method is known as the optonuclear quadrupolar effect or ONQ. From the paper:

[The ONQ effect] is second order in the electric field and nuclear spin I, as mediated by the quadrupole electric coupling, and is thus one of the nonlinear optical (NLO) responses of materials present in perfect crystals. Via the ONQ effect, nuclear spins can be coherently controlled by two-color photons, without electron spins as the media.

If you understood that, you should probably head over and read the rest of the paper. Meanwhile, the rest of us are waiting for our quantum Arduino.

Twist Promises Easier Quantum Programming

February 5, 2022 by 17 Comments

We keep trying to learn more about quantum computers. But the truth is, the way we program quantum computers — or their simulators — today will probably not have much in common with how we program them in the future. Think about it. Programming your PC is nothing like programming the ENIAC. So we expect we’ll see more and more abstractions over the “bare metal” quantum computer. The latest of these is Twist, from MIT.

According to the paper (and the video, below), Twist expresses entangled data and processes in a way that traditional programmers can understand. The key concept is known as “purity” of expressions which helps the compiler determine if data is actually entangled with another piece of data or if any potential entanglement is extraneous. A pure expression only depends on qubits it owns, while a mixed expression may use qubits owned by other expressions.

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Schrodinger’s Cat Lives

June 10, 2019 by 31 Comments

If quantum physics always sounded a little squirrelly to you, take heart. Yale researchers have announced that they can do what quantum physics claimed to be impossible: they can determine the state a quantum system will collapse to before it happens. This contradicts Schrodinger’s famous hypothetical cat that is superimposed as 50% alive and 50% dead at the same time. The research appears in Nature.

Schrodinger argued that until you open the box, the cat is half alive and half dead in the same way that a qubit can be in 50% of one state or another. When you observe it, you force the system to one state. Researchers at Yale, however, have found a way to use microwaves to indirectly monitor qubits to determine their state prior to the system making a jump. Unlike a normal observation which occurs too late, the Yale technique allows researchers to change the future state to their choice.

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