French quantum computing company increased the error correction level by 100000 times and raised 27 million euros

The 27 million euro round financing completed by Alice & Bob, a French quantum computing start-up, was led by elaia, bpifrance (through its digital risk fund), and supernova investment, with breega also participating. It will be used to launch the first fault-tolerant "cat qubit" computer in 2023 and realize the business model based on exponential quantum computing as a service.

Alice & Bob designed a different architecture, called cat qubit, which is a reference to Schrodinger's idea that a cat and something are in "two states" at the same time, to reduce errors in processing and the number of processors required to overcome these errors.

Although most methods of making quantum computer processors are based on superconducting circuits, the é Au peronnin, chief executive of Alice & Bob, said his company designed "another chip architecture" that can automatically correct errors.

Alice & Bob was founded by peronnin and Raphaël Lescanne. The founding team comes from French academia. At present, the number of employees is about 40, and more than half of them have doctorates. Alice & Bob is working with research laboratories in France.

What is a cat qubit?

At present, many quantum computing participants choose superconducting transmon qubit, which has a long coherence time and is easy to manufacture and operate. However, despite the continuous progress in the past 10 years, the improved speed of transmon error has slowed down, which makes active quantum error correction a necessary condition for further development.

Surface code is the most studied in theory among many quantum error correction strategies. However, due to the need for a large number of qubits, the implementation is still very challenging. Surface codes require a 2D qubit array to perform quantum error correction, and two types of errors need to be corrected, namely bit reversal and phase reversal. If there is only one error qubit, it will greatly reduce the difficulty of error correction.

Like many other Bose coding (such as GKP, binomial) error correction schemes, the cat qubit reduces the hardware required for error correction by using the large Hilbert space of the harmonic oscillator. Bose coding can disperse quantum information to more states with the same number of physical systems and achieve the same protection with fewer physical systems. This characteristic is called "hardware efficiency".

However, in this infinite-dimensional space, we need to be able to stabilize two specific states of quantum information coding. Cat qubits can achieve this independently.

Alice & Bob's method can stabilize the amplitude of α and two coherent states with opposite phases. This stability decreases exponentially α^2 Probability of bit reversal in 2 (from+ α To- α)， At the same time, it only linearly increases the phase reversal rate (the probability of losing 1 photon). To correct the remaining errors, linear repeat codes can be used to achieve a sufficiently small error rate.

To achieve this stability, they designed a nonlinear driving system to produce subharmonics. Due to the period-doubling, two stable states can be generated. When driven, the system has two stable states, namely coherent states| α〉 And|- α〉， They differ by only one π phase.

The level of error correction has increased 100000 times

In the arXiv preprint paper on March 14, Alice & Bob and Professor Zaki leghtas of the Physics Laboratory of the Higher Normal College in Paris proved that cat qubits can resist "bit flip" for a few minutes, which is nearly 100000 times the previous most advanced level.

The researchers measured a cat qubit (containing about 40 photons) with a bit flip time of more than 100 seconds.

As shown in the figure below, this measurement is completed by recording a single track, which randomly displays the cat qubit field, and there is a little bit of reversal (changing symbol).

Real-time 40-photon cat-qubit dynamics.

(Left) Histogram of the detected cat-qubit field demonstrating two oscillatory states with opposite signs. (Center) The single-time trajectory of the cat-qubit state revealing seldom jumps between the computational states. (Right) The cumulative distribution function of τjump is the duration between two consecutive jumps, labeled with the average.

For various cat sizes, we record time trajectories and extract the bit-flip time. The overall results are displayed in the graph below from which we distinguish two regimes. First, with a limited number of photons, the bit-flip time increases exponentially with the cat photon number. Then, when the bit-flip time reaches 2 minutes, it stops increasing with the cat photon number and saturates.

Exponential suppression of bit flips.The bit-flip time (y-axis, log-scale) is measured as a function of cat size in photon number (x-axis).

Next, reduce phase reversal

Peronnin said the start-up's next step - and why we won't see the product launch in another year - is to focus on using its cat qubits to reduce phase reversal (another type of error).

Alice & Bob has patented its hardware and software components. Although it does not intend to license it to other companies before using it to build its own computer, he points out that this is still an option.

Peronnin explained: "at present, we focus on manufacturing the whole machine because we must first prove that this technology can meet our commitments, but since we see some competitors and some of our technologies are patented, the problem will be open." It is worth mentioning that Amazon is also developing cat qubits.

"As deep technology investors, we believe that some of the biggest challenges facing society can be solved by using breakthrough technologies created by research laboratories. We believe that quantum computing is one of the most promising technologies to change the world and can promote extraordinary progress in a wide range of applications," said Sofia dahoune, investment director of elaia.

Link:

[1]https://thequantuminsider.com/2022/03/10/alice-bob-raises-27-million-euros-to-capitalize-on-scientific-advance/

[2]https://techcrunch.com/2022/03/09/alicebob-a-quantum-computing-startup-raises-30m-to-launch-its-first-fault-tolerant-cat-qubit-computers-in-2023/

[3]https://alice-bob.com/2022/03/10/one-hundred-seconds-bit-flip-time-in-a-superconducting-cat-qubit/