This week Microsoft announced a quantum-computing advancement: a measurement that looks like an electron split in half in a piece of wire. It will be of central importance if the company hopes to create a working quantum computer.
Big companies like IBM, Google, and Intel have built quantum computers with multiple qubits. It may appear that Microsoft is lagging behind—it hasn’t even debuted a single qubit yet. But Microsoft is working on its own quantum computer that incorporates extraordinary physics to overcome the technical barriers keeping their competitors back. If it gets everything working, this could be a really big deal.
Topological Quantum Computing
Quantum computers are harness the amazing principals quantum physics, the physics of the smallest particles, to perform calculations that would take the most powerful classical machines the whole length of the universe to solve.
While IBM and more recently Google have publicised huge advances in the numbers of qubits in their quantum devices (Google’s Bristlecone quantum chip is 72 qubits), the problem is that they are imprecise. The tiniest vibrations or energy from the outside environment could lead to an error in the calculations. Their qubits remain unreliable and difficult to scale.
However, Microsoft’s ‘topological’ quantum computers might drastically reduce that noise. Its researchers are making advances this year, including a paper published today in Nature, and they think they’ll have working qubits by the end of the year.
“One of our qubits will be as powerful as 1,000 or 10,000 of the noisiest qubits,”
According to Julie Love, director of quantum computing business development at Microsoft stated last week.
Computers calculate with bits—two-state systems, like a coin that can either be heads or tails. A quantum bit, or qubit, is the same, except the coin is flipping in a black box during the calculation. You’re allowed to set some initial values on each side of the coin—complex numbers of the form a+bi like you learned about in high school that, when manipulated, output how likely the coin is to land on heads or tails. You only know the value of the coin when you open the box. Computation is done by putting several coins tied together in the box at the same time and interacting them in a way such that those initial values combine mathematically. The output now relies on all of the coins, which makes certain combinations of heads or tails more likely and certain ones forbidden.
This system could be useful for lots of things, like advanced chemistry simulations or artificial intelligence. But the key is finding a sort of quantum heads-and-tails system where the two states can form a superposition (the black box), entangle (tying the coins together), and interfere (the likelihoods changing when coins are combined in the box). You also must find a system where the coins continue flipping even if you nudge the box, or find a way to build in redundancies to account for the nudges.
Microsoft researchers think that the key to overcoming the nudging problem is a topological system. They are engineered systems that retain some inherent qualities regardless of how you change them. They are so-called topological objects.
The researchers first needed to build their topological object. Microsoft specially fabricated piece of semiconducting wire made of indium antimonide, surrounded by superconducting aluminum. Cooling this wire to near-absolute zero in a magnetic field bestows the electrons with a collective behavior that forces certain electrical properties to take on discrete values.
How It Works
The quantum information would be stored in this system not in any single particle, but in the collective behavior of the entire wire. Manipulating the wire in the magnetic field could make it appear that half of an electron, or more accurately, a particle that’s halfway between an electron and not an electron, sits on either end. These so-called Majorana fermions, or Majorana zero-modes, are protected by the collective topological behavior of the system—you can move one around the wire without affecting the other. Ultimately this will lead to a far more stable overall system – where information is held in multiple places at the same time.
Reaction From The Community
Microsoft’s corporate vice president of Microsoft Quantum, Todd Holmdahl, hinted that they expect to make a discovery within a year.
It’s important to note that these topological qubits can’t do everything that other qubits can do yet, said Kouwenhoven. If you consider every possible combination of two quantum state as points on a sphere, these swapping operations can’t hit every point. But, Kouwenhoven hinted, “we have a plan.”
Physicists not involved with the research were excited about it for several reasons. “I think this paper is a big deal,” Smitha Vishveshwara, associate professor in the Department of Physics at the University of Illinois at Urbana-Champaign stated. “These ‘Majorana particles’ were originally theorized to exist in free space as their own antiparticle. Majoranas haven’t been discovered in empty space, but it’s cool to spot their analog in a system like this.”
Needless to say, Microsoft has invested millions of dollars to quite literally discover new physics in highly engineered systems in order to get its quantum computers to work. In many ways this explains why Microsoft doesn’t have a working pair of interacting qubits yet, though it has been simultaneously working on hardware and a user-facing development kit with a programming language.
Microsoft is confident that if it gets everything up and running, it will have the best qubits of all and will be able to quickly catch up to competitors. “We have a stable qubit, more stable than the other guys’,” said Love. “You can build a house out of bricks or two-by-fours, but that’s not what we build skyscrapers out of. Our qubits are like steel.”
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