Quantum state decoherence and thermal relaxation remain critical bottlenecks in Near-Intermediate Scale Quantum (NISQ) architectures. This paper introduces a co-designed 5-qubit pentagonal hardware topology integrated with an ultra-fast active FPGA feedback loop (< 50 ns) to suppress phase-kickback and environmental thermal degradation. Experimental field verification was conducted on the IBM Quantum platform using the 156-qubit ibm_fez physical processor (Job ID: d9ku512br2fc73e7t730). Under an unmitigated physical delay of 125,000 dt (~562.5 us), the proposed 5-qubit core maintained a state fidelity of 84% (860/1024 shots) in the dominant target state (|00001>). The architecture demonstrates that tight topology loop-backs combined with sub-microsecond feedback pipelines provide robust thermal stabilization without incurring massive error-correction pulse overheads.
Quantum state decoherence and thermal relaxation remain critical bottlenecks in Near-Intermediate Scale Quantum (NISQ) architectures. This paper introduces a co-designed 5-qubit pentagonal hardware topology integrated with an ultra-fast active FPGA feedback loop (< 50 ns) to suppress phase-kickback and environmental thermal degradation. Experimental field verification was conducted on the IBM Quantum platform using the 156-qubit ibm_fez physical processor (Job ID: d9ku512br2fc73e7t730). Under an unmitigated physical delay of 125,000 dt (~562.5 us), the proposed 5-qubit core maintained a state fidelity of 84% (860/1024 shots) in the dominant target state (|00001>). The architecture demonstrates that tight topology loop-backs combined with sub-microsecond feedback pipelines provide robust thermal stabilization without incurring massive error-correction pulse overheads.
This work demonstrates real-time predictive classical-quantum feedback control on the IBM Kingston superconducting quantum processor, characterizing the hardware latency bottleneck of dynamic Hamiltonian shaping. Decoherence in quantum systems is traditionally viewed as a technical obstacle arising from environmental noise; this paper interprets decoherence as the coupling of a localized system to a dissipative, high-entropy environmental field. An ancilla-based modular sensor architecture is introduced to facilitate real-time error syndrome extraction without collapsing the target state. A software-defined controller, implemented via a quantized Variational Autoencoder-Feed-Forward Network (VAE-FFN) pipeline and optimized via empirical threshold calibration under strict 4-bit latency constraints, provides predictive Hamiltonian control to stabilize the system boundary. The integration of a 3D volumetric topological complex outlines a geometric architecture designed to mitigate spatial error cascades. Through temporal delay sweeps, empirical telemetry demonstrates that the volumetric lattice achieves localized containment of non-commuting phase defects, dynamically exploiting coherent Larmor precession to constrain spatial error propagation. Furthermore, rigorous statistical repetition mapping reveals a critical Noisy Intermediate-Scale Quantum (NISQ) latency bottleneck. The empirical data establishes that the temporal cost of classical-quantum feed-forward routing incurs a marginal macroscopic fidelity reduction (-1.01%). Crucially, this study reframes this differential not as a systemic regression, but as an explicit architectural trade-off: prioritizing rigorous variance suppression and operational stability over unmitigated peak fidelity. By establishing a highly predictable, predictively controlled baseline, this framework explores practical control strategies consistent with Approximate Quantum Error Correction (AQEC) approaches, bounding the operational consequences of the Eastin-Knill constraint within an addressable temporal control protocol.
Abstract: The scalability of Noisy Intermediate-Scale Quantum (NISQ) devices remains fundamentally limited by stochastic decoherence, which traditional passive shielding and resource-heavy quantum error correction (QEC) struggle to overcome. Here, we propose a paradigm shift from passive noise mitigation to active internal phase stabilization. By integrating the Lie-algebraic renormalization (LA-ODR) framework with a dynamic model of temporal susceptibility (χ_τ), we derive a nonlinear control law for quantum coherence. We demonstrate that decoherence can be treated as a deterministic dynamical process governed by the feedback equation dχ_τ / dt = −α · Γ_τ · χ_τ + λ · (1 − χ_τ). Our numerical simulations confirm the formation of metastable coherence plateaus, where the effective qubit lifetime is extended significantly beyond the standard Lindbladian limit (e.g., from 100 µs to 1.5 ms in transmon-based models). We further specify a hardware-ready Temporal Phase-Locked Loop (TPLL) architecture, proving that with control latencies below 500 ns, active synchronization of the temporal metric becomes feasible on modern FPGA-based controllers. This framework provides a path toward fault-tolerant quantum computing by enabling fidelity-by-design at the physical layer, potentially providing a substantial reduction in QEC overhead by maintaining high physical fidelity prior to logical encoding. Keywords nonlinear phase stabilization; temporal susceptibility χτ; Lie-observable-dependent renormalization (LA-ODR); fixed-point Lindbladian; quantum decoherence; active feedback control; temporal phase-locked loop (TPLL); NISQ devices; superconducting qubits; cold atom arrays
Quantum decoherence, thermal bath fluctuations, parasitic inter-qubit cross-talk, and heavy-tailed dynamical shocks represent the fundamental physical barriers to scaling fault-tolerant quantum computing registers. Traditional mitigation strategies focus entirely on passive external isolation or massive physical-to-logical qubit overheads, which fail under non-Markovian noise regimes or substrate aging. This paper presents a definitive, internal architectural solution: an Active Error-Suppressing Topological Quantum Core governed by Realized Active Integrated Information (Φ_TAI) metrics. By injecting real-time thermodynamic feedback loops into a highly integrated, 3D cross-coupled quantum network, we mathematically throttle environmental dephasing. We validate this framework through a multi-stage credibility gauntlet, testing the system against:1. Non-Markovian 1/f colored noise (Stabilizing a QFI survival floor of 0.8277 through 100 cycles).2. Severe thermal ramps (Preserving a room-temperature quantum coherence of 0.6741 at 300 K).3. Intense capacitive cross-talk (χ = 0.80, achieving an over 77% drop in error to 0.2066).4. Compound heavy-tailed non-Gaussian dynamical shocks (Retaining a peak QFI floor of 0.9054). Furthermore, we outline the structural translation of this architecture into industry-standard Qiskit compiler layouts, expanding realized circuit integration from a fragile 0.2308 to an unassailable 2.6585. This layout natively insulates quantum phase data without logical qubit overheads, opening an asset-level path toward manufacturing ambient-temperature quantum hardware.
Abstract: Scalable fault-tolerant quantum computing confronts two fundamental physical bottlenecks: the cryogenic thermodynamic limit of dilution refrigeration, and the real-time decoding backlog in surface-code quantum error correction. While Google Quantum AI's 105-qubit Willow processor achieves physical gate error rates comfortably below the fault-tolerant threshold (Λ=p/pth<1), monolithic scaling beyond thousands of physical qubits precipitates catastrophic thermal saturation at the millikelvin stage. Furthermore, as error syndrome extraction cycles proceed at microsecond intervals, conventional classical decoders face an exponential decoding backlog that destroys quantum error suppression. This treatise establishes an integrated, physical-layer quantum architecture resolving these limits through three co-designed modules: (1) PHOENIX_BRIDGE, an optomechanical cavity interconnect executing high-fidelity coherent microwave-to-telecom photon transduction (λ=1550nm) for inter-cryostat distributed entanglement; (2) the Adaptive Phonon-Gate, a dynamic acoustic metamaterial bandgap modulator that directs non-equilibrium ballistic phonons away from Josephson junctions toward intermediate thermal sinks, attenuating quasiparticle poisoning and reducing 15mK heat dissipation by 85%; and (3) an AlphaQubit-driven real-time cryogenic decoding pipeline mapped to near-cryogenic (4K) FPGA/ASIC hardware, delivering sub-microsecond (750ns) syndrome decoding to strictly eliminate decoding backlog drift (dtdB≤0). We derive the underlying system Hamiltonians, acoustic phonon dispersion relations, non-equilibrium heat transport equations, and real-time queuing proofs, establishing a rigorous blueprint for scalable, multi-cryostat quantum computational infrastructure.
Abstract: The scalability of Noisy Intermediate-Scale Quantum (NISQ) devices remains fundamentally limited by decoherence, which conventional dynamical decoupling and quantum error correction only partially mitigate. This paper presents a transition from passive noise suppression to active dynamical stabilization through controlled modulation of the effective state-space metric. Within the Lie-algebraic observable-dependent renormalization (LA-ODR) framework, we introduce the Temporal Phase-Locked Loop (TPLL) — an active feedback controller that drives the temporal susceptibility χ_τ toward the globally stable fixed point χ_τ* = λ_nat/(λ_ctrl + λ_nat) via the Kyiv–Ohnishi hybrid flow: dχ_τ/dt = −α·Γ₀·(χ_τ)^(β+1) − λ_ctrl·χ_τ + λ_nat·(1−χ_τ). Numerical simulations demonstrate the emergence of metastable coherence plateaus extending coherence times from ~100 µs to ~1.5 ms under realistic hardware benchmarks (FPGA latency Δt < 500 ns). Three operationally distinct zones are characterized by χ_τ thresholds, and two experimentally distinguishable signatures — Phase Inertia and Avalanche Collapse — are predicted. The TPLL is compared with dynamical decoupling, quantum error correction, and discrete time crystals, establishing complementarity rather than competition. The mathematical foundations rest on four global stability theorems via Lyapunov analysis and Chiba renormalization-group flow. Index Terms: Quantum coherence; decoherence control; temporal susceptibility; LA-ODR; Temporal Phase-Locked Loop (TPLL); Kyiv–Ohnishi flow; NISQ devices; open quantum systems; Lyapunov stability; Lie algebra; FPGA quantum control; nonlinear dynamics.
As superconducting and silicon-spin quantum processors scale from hundreds to thousands of physical qubits, the interconnect bottleneck between room-temperature classical electronics and mK cryogenic quantum processors poses a critical physical and architectural barrier. Low-latency control loops—essential for Quantum Error Correction (QED), fast reset protocols, and adaptive quantum algorithms—are strictly constrained by thermal load budgets, speed-of-light signal latency across thermal stages, and the bandwidth limits of coax lines. This paper presents a detailed architectural framework for next-generation quantum-classical interfaces. We investigate the transition from traditional, room-temperature arbitrary waveform generators (AWGs) connected via coaxial lines to co-integrated, cryo-CMOS, and single-flux-quantum (SFQ) digital-to-analog and digital signal processing control layers operating directly at the 4 K and 20 mK stages. We evaluate thermal transport, power dissipation, signal attenuation, and physical routing constraints, proposing a heterogeneous hybrid-control topology that satisfies latency budgets below 100 ns while remaining within the tight thermal limits of modern dilution refrigerators.