We report the observation of long-range dynamical protection and coherent transport of two-qubit entangled states across discrete 1D lattice chains on a 156-qubit superconducting quantum processor (ibm_marrakesh). By combining an affine geometric phase gradient with periodic CPMG dynamical decoupling and Hermitian conjugate frame unwinding, we suppress continuous dephasing, spatial wavepacket dispersion, and accumulative cross-resonance errors. The protocol achieves an unmitigated Bell state fidelity of 97.92% +/- 0.10% across 512 physical SWAP gates (1,536 native two-qubit hardware operations) and maintains an unmitigated fidelity of 97.93% +/- 0.22% (Tr(rho^2) = 0.9591) through 1,024 physical SWAPs (3,072 native pulses), contrasting with bare unmitigated transport decay (F < 1%). We demonstrate spatial transport scaling across up to 101 contiguous transmons (89.06% fidelity across 198 SWAPs), confirm the attractor basin geometry under continuous 3D Bloch sphere parameter sweeps (theta in [0, 2pi]), and validate sensitivity to intentional single-qubit phase and bit-flip defect injections.
We report the observation of long-range dynamical protection and coherent transport of two-qubit entangled states across discrete 1D lattice chains on a 156-qubit superconducting quantum processor (ibm_marrakesh). By combining an affine geometric phase gradient with periodic CPMG dynamical decoupling and Hermitian conjugate frame unwinding, we suppress continuous dephasing, spatial wavepacket dispersion, and accumulative cross-resonance errors. The protocol achieves an unmitigated Bell state fidelity of 97.92% +/- 0.10% across 512 physical SWAP gates (1,536 native two-qubit hardware operations) and maintains an unmitigated fidelity of 97.93% +/- 0.22% (Tr(rho^2) = 0.9591) through 1,024 physical SWAPs (3,072 native pulses), contrasting with bare unmitigated transport decay (F < 1%). We demonstrate spatial transport scaling across up to 101 contiguous transmons (89.06% fidelity across 198 SWAPs), confirm the attractor basin geometry under continuous 3D Bloch sphere parameter sweeps (theta in [0, 2pi]), and validate sensitivity to intentional single-qubit phase and bit-flip defect injections.
Abstract Scaling quantum information processing on planar, nearest-neighbor superconducting transmon architectures requires the coherent distribution of entangled states across extensive multi-qubit distances. Standard SWAP routing networks suffer from rapid, exponential fidelity decay driven by spatial wavepacket dispersion, coherent cross-resonance drive errors, and environmental dephasing. In this work, we propose and numerically validate a Dual-Anchor Floquet Cavity protocol capable of shuttling entangled Bell pairs across macroscopic 1D transmon chains with theoretical zero-dispersion unitary closure (U_cycle = I). By combining an affine geometric phase gradient with synchronized Y ⊗ Y boundary echo reflections and Hermitian conjugate spatial unwinding, the protocol eliminates intermediate odd-cycle micro-motion lag, establishing a strictly invariant attractor limit cycle. Using Matrix Product State (MPS) simulations bounded at entanglement bond dimension χ = 2, we verify exact 100.00% target singlet fidelity, 1.0000 state purity, and maximal non-locality (S = 2.8284) across 17, 102, and 1,002 transmon sites through circuit depths exceeding 31,000. Furthermore, under open-system Lindbladian noise models (T₁ = 150 µs, T₂ = 100 µs, and 0.4% two-qubit depolarizing rate), the architecture exhibits intrinsic dynamical decoupling, with exponential Zero-Noise Extrapolation (ZNE) recovering near-unity fidelity across 720 native entangling operations. This work provides an exact theoretical parameterization and simulation foundation for future experimental implementation on physical superconducting quantum processors. **Acknowledgements** The author acknowledges Gemini (Google) for interactive conceptual dialogue, mathematical derivation scaffolding, and numerical simulation workflow validation.
We report the multi-system physical benchmarking of non-equilibrium quantum hydrodynamic transport, extreme-depth variational circuits, and three-dimensional biomolecular tensor fields across three commercial 156-qubit IBM Heron superconducting transmon processors: ibm_fez, ibm_marrakesh, and ibm_kingston. Utilizing Qiskit 2.x and native two-qubit Controlled-Z (CZ) pulse primitives with tunable couplers, we execute fourteen consecutive production workloads spanning circuit depths up to 547 gate cycles, on-chip transmon registrations up to 100 active physical qubits (Project APEX-HYDRO, Job dateauqhcrkc73du2gr0; 840 native CZ gates), and full-chip macroscopic entanglement across all 156 transmon sites. In our landmark 100-qubit hydrodynamic benchmark on ibm_kingston, we physically measure non-equilibrium wavepacket spreading on a connected heavy-hexagonal transmon subgraph, observing Kardar-Parisi-Zhang (KPZ) superdiffusive transport with dynamical critical exponent z = 1.52 ± 0.04 in the integrable 1D regime (lambda=0), crossing over to conventional diffusion (z = 1.98 ± 0.05) upon introducing heavy-hex transverse cross-couplers (lambda=0.5). We prove that classical Matrix Product State (MPS) simulations truncate at quench time t* ≈ 2.12 hbar/J for bond dimensions chi <= 128, demonstrating an operational quantum advantage boundary on superconducting silicon. Concurrently, we achieve sustained variational coherence across 29 entangling layers (435 native CZ gates, Depth 547) in 1.12 seconds on-chip (Job dat840jojkfs738qag4g), and simulate 3D anisotropic stress tensors derived from AlphaFold3 biomolecular coordinates across 64 qubits on ibm_fez. All 14 production workloads completed with a 100.0% execution reliability, establishing quantitative design rules for utility-scale superconducting quantum simulation.
Quantum processors based on superconducting circuitry have reached the scale of hundreds of qubits and demonstrated computational capabilities that challenge state-of-the-art classical methods for carefully designed problems. Despite these advances, fundamental questions persist over how to best improve and scale the computational power of this emerging technology. Most transmon-based quantum processors encode information in two-level systems, or qubits, leaving the rich multilevel structure of the transmon largely unexploited. In this thesis, we demonstrate how the capabilities of these devices can be meaningfully extended by harnessing this intrinsic multilevel structure to encode qudits — d-level quantum systems that access a larger and more connected Hilbert space than their qubit counterparts. We begin by demonstrating universal single-qudit operation before turning to microwave-activated entanglement to realize scalable two-qudit gates. We present a high-fidelity, fully entangling two-qutrit CZ gate based on a novel tunable cross-Kerr mechanism. We further explore two-qudit gates that selectively entangle subspaces of the full Hilbert space via two-photon multipartite Raman transitions, employing these operations to generate large entangled states across a transmon array. To address the noisy nature of near-term qudit computation, we introduce and characterize error suppression techniques for qudit circuits, including dynamical decoupling and quantum error mitigation. We then synthesize these directions by exploring simulations of quantum systems that have innate multilevel interactions and are therefore well tailored to qudit operation. First we investigate digital quantum simulations of collective neutrino oscillations and the spin-1 truncated Abelian Higgs model, finding error mitigation methods critical for improving circuit performance. Finally, out of equilibrium --- or Floquet --- spin-1 systems are realized using an array of 15 superconducting qutrits to probe a novel Z3 discrete time crystalline (DTC) phase of matter with intrinsically chiral interactions. This DTC result demonstrates that native qudit hardware provides powerful access to non-equilibrium phases rooted in higher discrete symmetries, opening a route to a broader landscape of dynamical orders beyond the Z2 Ising paradigm.
Precise control of multi-qubit architectures remains a critical bottleneck in superconducting quantum processors. In this work, we investigate the synthesis of high-fidelity quantum operations and state transfer protocols within an extended superconducting linear chain, scaling from three to seven sites. Using Floquet theory, we model the periodic drive as a train of delta-like pulses, mapping the quantum control problem onto quasi-energy resonance conditions. Combining the Baker-Campbell-Hausdorff expansion with Floquet spectral decomposition, we analytically identify optimal driving parameters, refined via the Covariance Matrix Adaptation Evolution Strategy (CMA-ES). In the three-qubit architecture, this enables high-fidelity synthesis of the iSWAP gate. Extending to a seven-site chain, we implement periodic trains of finite-width Gaussian pulses to activate distinct double-excitation transport channels with ultra-short gate durations t_gate (~170 ns). This achieves a clear scale separation from energy-relaxation times (T1) typical of fixed-frequency transmon devices with tunable couplers, such as IBM Quantum hardware. Finally, we benchmark stability under realistic imperfections, revealing a heightened sensitivity to static parameter disorder at the sub-percent level (eta ~ 10^-3) driven by spectral crowding, and discuss how closed-loop topologies could mitigate this constraint. This framework bridges time-periodic control theory and practical quantum gate engineering.
The scalability of Noisy Intermediate-Scale Quantum (NISQ) devices is currently constrained by material defects, specifically Two-Level Systems (TLS) that induce resonant decoherence in superconducting qubits. This study presents a comprehensive experimental analysis using the IBM Quantum ibm_fez processor to demonstrate "Software-Defined Hardware" optimization. By employing a novel "Instruction-Level Calibration Injection" technique, we bypass standard compiler constraints to inject continuous off-resonant AC Stark drives (Nshots=4096). Methodology The experiment utilizes a Floquet engineering approach to perform pulse-level Hamiltonian engineering. We implement custom instruction-level calibrations to apply continuous off-resonant AC Stark drives, effectively modifying the qubit frequency to avoid resonant interactions with defect states. Key Findings The application of this protocol yielded three primary results: Spectral Decoupling: Successfully restored Ramsey fringes in a defect-limited qubit (Q150), achieving a coherence time of T2∗≈6.36μs. Protocol Benchmarking: The "Stark Rescue" protocol demonstrated a statistical advantage over standard CPMG dynamical decoupling. It extended coherence time by 11.3% (T2Stark=8.17μs vs. T2CPMG=7.34μs; p=0.042, Bootstrap t-test). Topological Simulation: Digital simulation of a topological domain wall under engineered correlated noise revealed a sigmoidal stability threshold (SSE≈0.0008), significantly outperforming standard exponential models (SSE≈0.0085). Conclusion These results confirm that pulse-level Hamiltonian engineering can effectively reclaim compromised hardware resources on current NISQ platforms. Keywords NISQ, Superconducting Qubits, Two-Level Systems (TLS), Floquet Engineering, AC Stark Effect, IBM Quantum, Dynamical Decoupling, Quantum Control.
Multilevel qudit systems are increasingly being explored as alternatives to traditional qubit systems due to their denser information storage and processing potential. However, qudits are more susceptible to decoherence than qubits due to increased loss channels, noise sensitivity, and crosstalk. To address these challenges, we develop protocols for dynamical decoupling (DD) of qudit systems based on the Heisenberg-Weyl group. We implement and experimentally verify these DD protocols on a superconducting transmon processor that supports qudit operation based on qutrits (d=3) and ququarts (d=4). Specifically, we demonstrate single-qudit DD sequences to decouple qutrits and ququarts from system-bath-induced decoherence. We also introduce two-qudit DD sequences designed to suppress the detrimental cross-Kerr couplings between coupled qudits. This allows us to demonstrate a significant improvement in the fidelity of time-evolved qutrit Bell states. Our results highlight the utility of leveraging DD to enable scalable qudit-based quantum computing.