IBM and Rutgers Control Quantum Chaos Across 100 Qubits

Researchers from Rutgers University, IBM Quantum, and collaborating academic institutions have demonstrated real-time quantum feedback control across 100 qubits on a 156-qubit IBM Quantum Heron superconducting processor (ibm_fez), according to Quantum Computing Report. The study, published in Nature Physics, implements adaptive quantum circuits that interleave entangling gates with mid-circuit measurements and resets, providing experimental validation of non-unitary dynamics considered critical for scalable quantum error correction.

What the Experiment Showed

The experiment executed nearly 5,000 two-qubit entangling gates and nearly 5,000 mid-circuit measurement-based resets across 100 linearly connected qubits. By stochastically pitting information-scrambling operations, described as a quantum analog of the classically chaotic Bernoulli map, against local resets that push qubits toward the zero state, the team observed and characterized a dynamical control-induced phase transition (CIPT) between a chaotic volume-law phase and a controlled, unentangled phase.

According to the reported parameters, the system moved through four regimes depending on the control rate (p): a chaotic volume-law phase at low control rates (0 ≤ p < 0.3) with extensive entanglement and a positive Lyapunov exponent; a chaotic area-law phase (0.3 < p < 0.5) with subextensive entanglement; a critical point near p ≈ 0.5, measured at p_c = 0.495(1) with critical exponents ν = 1.05(2), z = 2.08(1), and β = 1.05(2); and a controlled phase at higher control rates (0.5 < p ≤ 1.0) where the system locks into an unentangled fixed state.

Confirming Genuine Quantum Behavior

To distinguish true coherent quantum dynamics from classical noise, the researchers measured the variance of shot-to-shot quantum fluctuations across 10,000 shots per circuit configuration. Comparing the experimental distributions against classical dephasing Markov models using Kullback-Leibler divergence confirmed that the processor sampled a genuine quantum random process rather than purely incoherent stochastic noise.

Quantum Computing Report describes the study as one of the largest experimental realizations of real-time feedback and non-unitary adaptive circuits to date, validating theoretical matrix product state models and statistical mechanics mappings on physical hardware. The peer-reviewed study appears in Nature Physics, with additional detail available in an institutional report from Rutgers Today and a technical preprint on arXiv.