quantum computing

48 Articles

Quantum Computing On A Commodore 64 In 200 Lines Of BASIC

July 4, 2023 by 17 Comments

The term ‘quantum computer’ gets usually tossed around in the context of hyper-advanced, state-of-the-art computing devices. But much as how a 19th century mechanical computer, a discrete computer created from individual transistors, and a human being are all computers, the important quantifier is how fast and accurate the system is at the task. This is demonstrated succinctly by [Davide ‘dakk’ Gessa] with 200 lines of BASIC code on a Commodore 64 (GitHub), implementing a range of quantum gates.

Much like a transistor in classical computing, the qubit forms the core of quantum computing, and we have known for a long time that a qubit can be simulated, even on something as mundane as an 8-bit MPU. Ergo [Davide]’s simulations of various quantum gates on a C64, ranging from Pauli-X, Pauli-Y, Pauli-Z, Hadamard, CNOT and SWAP, all using a two-qubit system running on a system that first saw the light of day in the early 1980s.

Naturally, the practical use of simulating a two-qubit system on a general-purpose MPU running at a blistering ~1 MHz is quite limited, but as a teaching tool it’s incredibly accessible and a fun way to introduce people to the world of quantum computing.

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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Quantum Interconnects Get Faster

February 17, 2023 by 2 Comments

If you are a retrocomputer fan, you might remember when serial ports were a few hundred baud and busses ran at a few megahertz at the most. Today, of course, we have buses and fabric that can run at tremendous speeds. Quantum computing, though, has to start from scratch. One major problem is that jockeying quantum states around for any distance is difficult and slow. Part of it is that qubits decay rapidly, so you don’t have much time. They are also generally susceptible to noise and perturbation by outside forces. So many quantum machines today are limited by how much they can cram on one chip since there isn’t a good way to connect to another chip. The University of Sussex thinks it has improved the outlook for quantum interconnects with a technique they claim can move qubits around at nearly 2,500 links per second.

The technique, called UQ Connect, uses electric field links to connect multiple chips using trapped ions for qubits. If you want to read the actual paper, you can find it in Nature Communications.

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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.

Inca Knots Inspire Quantum Computer

July 28, 2022 by 19 Comments

We think of data storage as a modern problem, but even ancient civilizations kept records. While much of the world used stone tablets or other media that didn’t survive the centuries, the Incas used something called quipu which encoded numeric data in strings using knots. Now the ancient system of recording numbers has inspired a new way to encode qubits in a quantum computer.

With quipu, knots in a string represent a number. By analogy, a conventional qubit would be as if you used a string to form a 0 or 1 shape on a tabletop. A breeze or other “noise” would easily disturb your equation. But knots stay tied even if you pick the strings up and move them around. The new qubits are the same, encoding data in the topology of the material.

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Google Quantum, Virtually

July 28, 2022 by 18 Comments

Want to try a big quantum computer but don’t have the cash? Google wants to up your simulation game with their “Quantum Virtual Machine” that you can use for free.

On the face of it, it sounds like marketing-speak for just another quantum simulator. But if you read the post, it sounds like it attempts to model effects from a real Sycamore processor including qubit decay and dephasing along with gate and readout errors. This forms what Google calls “processor-like” output, meaning it is as imperfect as a real quantum computer.

If you need more qubits than Google is willing to support, there are ways to add more computing using external compute nodes. Even if you have access to a real machine of sufficient size, this is handy because you don’t have to wait in a queue for time on a machine. You can work out a lot of issues before going to the real computer.

This couldn’t help but remind us of the old days when you had to bring your cards to the central computer location and wait your turn only to find out you’d made a stupid spelling mistake that cost you an hour of wait time. In those days, we’d “desk check” a program carefully before submitting it. This system would allow a similar process where you test your basic logic flow on a virtual machine before suffering the wait time for a real computer to run it.

Of course, if you really need a quantum computer, the simulation is probably too slow to be practical. But at least this might help you work out the kinks on smaller problems before tackling the whole enchilada. What will you do with a quantum computer? Tell us in the comments.

Google, of course, likes its own language, Cirq. If you want a leg up on general concepts with a friendly simulator, try our series.

Quantum Circuit Uses Just A Few Atoms

June 25, 2022 by 5 Comments

Researchers at the University of New South Wales and a startup company, Silicon Quantum Computing, published results of their quantum dot experiments. The circuits use up to 10 carbon-based quantum dots on a silicon substrate. Metal gates control the flow of electrons.  The paper appears in Nature and you can download the full paper from there.

What’s new about this is that the dots are precisely arranged to simulate an organic compound, polyacetylene. This allowed researchers to model the actual molecule. Simulating molecules is important in the study of exotic matter phases, such as superconductivity. The interaction of particles inside, for example, a crystalline structure is difficult to simulate using conventional methods. By building a model using quantum techniques on the same scale and with the same topology as the molecule in question, simulation is simplified.

The SSH (Su-Schreffer-Heeger) model describes a single electron moving along a one-dimensional lattice with staggered tunnel couplings. At least, that’s what the paper says and we have to believe it. Creating such a model for simple systems has been feasible, but for a “many body” problem, conventional computing just isn’t up to the task. Currently, the 10 dot model is right at the limit of what a conventional computer can simulate reasonably. The team plans to build a 20 dot circuit that would allow for unique simulations not feasible with classic computing tech.

The dots are made with a scanning tunneling microscope and there is a Goldilocks effect regarding the size of the dots. If they are too small, the energy levels are overwhelmed by phosphorous donors. Too large, and capacitive coupling between dots makes the system unstable.

We’ll admit, the science in the paper is pretty dense. But the Methods section outlines what it takes to create something like this. You’ll need silicon, high-temperature ovens, and the ability to handle exotic gasses and perform lithography. Pretty much an IC fab in your basement. However, we did wonder if anyone homebrewing chips had ever tried STM lithography like this as an alternative to optical lithography. Seems like it might be possible.

We can’t help with some of the more exotic gear, but if you want to build an STM, it has been done. While you can make quantum dots in your kitchen, we don’t think they are going to work the same.