Alice and Bob, a French quantum computing startup, is built on a philosophy that building better qubits that require little error-correction is a better approach than building a device with many qubits that are too vulnerable to errors.
It’s a case of quality over quantity.
Now, the company is enlisting the help of one of the originators of superconducting quantum computing — and someone who is philosophically in tune with Alice and Bob’s quality-first approach.
“As one of the originators of superconducting qubits, I have a great interest in seeing this technology be pushed to its maximum possibility.”
The company announced that Michel Devoret, the Frederick W. Beinecke Professor of Applied Physics, Yale University, will serve as a scientific adviser to Alice and Bob.
Devoret said he joined the team as adviser because he wants to see quantum science generate practical applications that help people.
“As one of the originators of superconducting qubits, I have a great interest in seeing this technology be pushed to its maximum possibility,” said Devoret, who graduated from Ecole Nationale Superieure des Telecommunications in Paris and later received his doctorate from Paris University in 1982. “Anything I can do to help industries and labs go further – I will do. It is wonderful that there are industries that are interested in this domain of research. I think that when this happens, a discovery is truly validated.”
He said there are parallels to how superconductivity moved from laboratories into the real world.
“When there are applications, it means you really understand the fundamental discoveries on which they are based,” he said. “Let’s take superconductivity. You can now actually see this phenomenon in a computer simulation. You do simulations of interacting electrons, and they will tell you that there is a phase of electrons which superconducts. But this phenomenon fully exists when you build an MRI machine, or when superconductivity is used for other mass applications like encephalography, the measurement of tiny currents inside the brain.”
What Will Quantum Be Good For
Devoret said that some applications for advanced science and technology are often hard to predict. The quantum era may then be at a stage that is similar to the dawn of the electric age in the 19th century that saw innovators create some applications that were beyond initial predictions for the technology.
“Think about the beginning of electricity, let’s say electricity of the mid 1800s,” Devoret said. “(Michael) Faraday was giving popular lectures on electricity and magnetism at the Royal Society — People would always ask him questions about applications of electricity and “what electricity will be good for?” At the time, there were no elevators, no electric trains. And he had to use this wonderful answer, which was: ‘well, what is the use of a baby?’ We now think of electricity as a practical physical science, but once in the past, in the 18th or mid-19th century, it was actually a purely gratuitous physics field.”
Devoret is considered a pioneer in the research of superconducting quantum circuit approach to quantum computing. He spent two post-doctoral years working on macroscopic quantum tunneling and energy level quantization with John Clarke’s laboratory at the University of California, Berkeley and then pursued this research on quantum mechanical electronics at University of Paris-Saclay.
“I think the fascinating thing about the quantum computer is that it teaches you quantum mechanics like no other thing can, because you get to practice with quantum behavior at your scale.”
Quantum Computing’s Hidden Benefit
Devoret added that he’s interested in helping the emerging quantum industry for another reason. He said there is a hidden value of these efforts to build and program quantum computers, something that won’t show up in a company’s balance sheet or in a startup’s valuation. By regularly working with these devices and interacting with quantum science, people will be continually increasing their knowledge about quantum mechanics and, therefore, nature itself.
“I think the fascinating thing about the quantum computer is that it teaches you quantum mechanics like no other thing can, because you get to practice with quantum behavior at your scale,” said Devoret. “You get to see it, not as mathematical equations, not as a piece of math, but really as something quite practical.”
“We definitely are inheriting this vision of efficient encoding and trying to solve the problem from the ground up, instead of facing it head first, through scaling.”
Théau Peronnin, CEO of Alice and Bob, said that the company and his fellow co-founders were deeply inspired by Devoret’s work and the vision behind efficient encoding.
“We just arrived at a time where the mindset of the field changed, where we needed a company to bring the resources, whether they’re financial or human, to continue developing this technology and transfer it to the real world,” said Peronnin. “We definitely are inheriting this vision of efficient encoding and trying to solve the problem from the ground up, instead of facing it head first, through scaling.”
Peronnin said enlisting Devoret’s help will do more than just strengthen the company’s scientific foundation, the relationship will also help to keep simplifying quantum error correction through ever more efficient encoding.
“First, we have to acknowledge Michel was a key part of the invention of this whole approach of hardware efficiency, but it is a bit more profound than just the cat qubits, which are the tip of the iceberg of the new generation of qubits that are arriving,” said Peronnin. “In Michel’s group there have been other experiments that go beyond just error-correction. And so for the company, it means a very strong acknowledgement of that scientific heritage and vision. And this is why we’re extremely proud to have Michel among us. And we’re also hoping it will spark young physicists to join us in trying to simplify quantum computers before trying to actually dive into complexity.”
Cat Qubit
As Peronnin mentioned, the cat qubit — which gets its name from Schrödinger’s cat, quantum’s most famous feline thought experiment — is pivotal to Alice and Bob’s approach. Devoret and his team pioneered the use of cat-qubits, publishing the first experimental demonstration in Science in 2015.
Qubits can randomly flip between quantum superpositions, which requires error-correction to sort out. One error-correction method just adds greater redundancy, requiring many more physical qubits for each logical qubit.
However, a cat-qubit encodes an effective qubit into superpositions of two states within a single electronic circuit, such as a superconducting microwave resonator. The phase of the oscillations corresponds to the two states of the cat-qubit.
Devoret likens it to a swing.
“You have the oscillator’s state pointing in one direction, imagine it as a child’s swing,” said Devoret. “Imagine that the swing is swinging back and forth. But now you can imagine that the swing is put in a superposition of two states of motion, with two opposite angles from the vertical. So instead of one swing, oscillating back and forth, you one half swinging back and forth and the other half swinging forth and back. This you can do in quantum mechanics, because objects can be in two different positions at once. In the cat qubit, such motion is the kind of oscillation going on in the superconducting resonator.”
The approach offers several advantages. It features a combination of fast quantum control and robustness against errors. That makes it a more stable platform for quantum information processing.
Achievements
Devoret’s “quantronics group” achieved other several scientific advances, including the measurement of the traversal time of tunneling, the invention of the single electron pump, the first measurement of the effect of atomic valence on the conductance of a single atom and the first observation of the Ramsey fringes of a superconducting artificial atom, the quantronium. Recently, his group realized the full quantum error correction of a qubit, using amplifiers that they developed to detect single microwave quanta.
Devoret was the recipient of the John Stewart Bell Prize, which he received jointly with Rob Schoelkopf in 2013. In 2014, he, along with John Martinis and Rob Schoelkopf, were awarded the Fritz London Memorial Prize.
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