Quantum simulation of the most complex biological molecules is no longer a distant dream. On 9 October 2025, Alice & Bob, the Paris‑Boston quantum‑computing start‑up, announced that its cat‑qubit architecture can cut the physical qubit count required to model the ground state energies of the cytochrome P450 enzyme and the nitrogen‑fixing FeMoco cluster by a factor of 27. The company’s claim rests on a detailed resource‑estimation study that shows the total number of physical qubits would fall from 2.7 million to just 99 000, keeping logical error rates and run times unchanged.
How Cat Qubits Slash Physical Qubit Needs 27x
Cat qubits are a form of bosonic encoding that protects logical information by exploiting superpositions of coherent states, hence the “cat” name. Alice & Bob’s team applied this error‑resistant encoding to a benchmark problem that had previously been tackled by Google in 2021. That earlier study estimated that simulating the ground state of FeMoco would require roughly 2.7 million physical qubits when using conventional superconducting transmon qubits. By contrast, Alice & Bob’s preliminary analysis, published in a blog post titled Quantum Resource Estimation for Ground State Energy of FeMoco and P450 on Cat Qubits, finds that the same simulation can be performed with only 99 000 physical qubits.
The reduction is not merely a theoretical curiosity. The study keeps all other parameters constant: the logical error rate, which governs how often a fault propagates to a logical qubit, and the total run time of the simulation. In other words, the 27‑fold savings come from the intrinsic robustness of the cat‑qubit encoding, not from looser accuracy requirements or longer computation times. This level of hardware efficiency is a decisive step toward a fault‑tolerant quantum computer that can tackle real‑world chemistry problems.
Quantum Simulation of P450 and FeMoco Molecules
The two molecules at the heart of the study, cytochrome P450 (P450) and the iron, molybdenum cofactor (FeMoco), represent two of the most challenging targets for quantum chemistry. P450 is a heme enzyme that metabolises roughly 75 % of all drugs in the human body. Its ability to oxidise a wide range of substrates makes it a coveted target for pharmaceutical design, yet its complex electron transfer pathways are difficult to model with classical algorithms. FeMoco, on the other hand, is the active site of nitrogenase, the enzyme that converts atmospheric nitrogen into ammonia in certain bacteria. The Haber, Bosch process that industrially synthesises ammonia consumes 1,2 % of global energy and emits up to 3 % of the planet’s carbon emissions. A better understanding of FeMoco could pave the way for greener, biologically inspired nitrogen fixation.
Classical supercomputers struggle to capture the full quantum behaviour of these molecules because the number of interacting electrons scales exponentially with system size. Even the most powerful clusters cannot simulate the electron correlation effects that dominate the ground state energies of P450 and FeMoco. In contrast, a quantum computer can, in principle, encode the entire electronic wavefunction directly. The cat‑qubit approach promises to bring this capability within reach by dramatically reducing the hardware overhead.
Théau Peronnin on Unlocking Drug Discovery Potential
Théau Peronnin, CEO of Alice & Bob, underscored the broader impact of the findings. In a statement accompanying the blog post, he said:
“Quantum simulation can access the mechanisms of important molecules with unprecedented precision,” , Théau Peronnin, CEO of Alice & Bob
“Cat qubits significantly enhance the hardware efficiency required by these simulations, unlocking promising applications in drug discovery and the invention of better production methods for key chemicals.”
Peronnin’s remarks point to a dual benefit. First, more accurate simulations of P450 could enable medicinal chemists to predict how candidate drugs will be metabolised, reducing late‑stage failures. Second, a deeper understanding of FeMoco could inform the design of catalysts that mimic biological nitrogen fixation, potentially lowering the energy cost of ammonia production.
The company’s leadership team, advised by Nobel‑prize‑winning scientists, has already demonstrated that cat‑qubit technology can cut hardware requirements for large‑scale quantum computers by up to 200 times compared with competing approaches. The 27‑fold reduction in qubits required for these two molecules is a concrete illustration of that promise.
The Ground State Energy Breakthrough for Key Chemicals
Ground‑state energy calculations are central to quantum chemistry because they determine a molecule’s stability, reactivity, and response to external stimuli. Accurate ground‑state energies are essential for predicting reaction pathways, binding affinities, and spectroscopic signatures. The resource‑estimation study shows that, with cat qubits, Alice & Bob can compute these energies for P450 and FeMoco within a timeframe that is competitive with classical methods, while maintaining error rates that would be unacceptable for conventional qubit architectures.
The study also highlights the scalability of the approach. By keeping logical error rates and run times constant, the authors argue that the same methodology can be applied to larger biomolecules and more complex catalytic systems. The implication is that a fault‑tolerant quantum computer built on cat qubits could become a practical tool for chemists within the next five years, a horizon that aligns with Alice & Bob’s own forecast for when early fault‑tolerant devices will surpass classical supercomputers on chemical simulation tasks.
The company’s recent report, which accompanies the blog post, lays out a roadmap for achieving these milestones. It details the engineering challenges that remain, such as scaling up the number of physical qubits while maintaining coherence, and outlines the milestones required for a commercially viable quantum platform.
Alice & Bob’s announcement marks a significant stride toward the long‑sought goal of fault‑tolerant quantum computing. By demonstrating that cat qubits can reduce the physical qubit count for two of the most demanding chemical simulations by a factor of 27, the company provides a concrete pathway to practical quantum chemistry. If the company can translate these theoretical savings into a working machine, the ripple effects could transform drug discovery, reduce the carbon footprint of fertilizer production, and usher in a new era where quantum computers routinely tackle problems that lie beyond the reach of classical supercomputers.
