Quantum Material’s Dynamics Remotely Controlled, Bridging Simulator and Computer Worlds
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Scientists are increasingly focused on harnessing quantum mechanics to design and control novel materials. Andrei Vrajitoarea from New York University, Gabrielle Roberts from the University of Chicago, and Kaden R. A. Hazzard from Rice University, alongside Jonathan Simon and David I. Schuster et al., demonstrate a significant step towards this goal by merging the strengths of analog quantum simulators and digital quantum computers. Their research details the embedding of digital control within the analog evolution of a synthetic quantum material, specifically a Bose-Hubbard circuit, allowing for Hamiltonian-level control and the creation of previously inaccessible strongly-correlated states. This hybrid approach not only guides the system into novel phases of matter, exhibiting both solid and fluid characteristics, but also enhances coherence through many-body echo techniques, ultimately illustrating a pathway for improved sensing and materials characterisation via entanglement between quantum computers and quantum matter. Entangling Bose-Hubbard circuits and qubits for hybrid quantum control Scientists have demonstrated a quantum-controlled synthetic material by entangling a Bose-Hubbard circuit with an ancilla qubit. This breakthrough merges the strengths of analog quantum simulators and digital quantum computers, paving the way for new capabilities in state preparation, characterization, and dynamical control of many-body systems. The research details a novel approach to Hamiltonian-level control, where the lattice potential landscape of a Bose-Hubbard circuit is directly manipulated through entanglement with a single qubit. This allows for dynamics under a superposition of different lattice configurations, guiding the system towards previously inaccessible strongly-correlated states. Specifically, the work successfully orders photons into superpositions of solid and fluid eigenstates, effectively creating a “photonic transistor” where quantum logic is embedded within the analog dynamics of a many-body system. By leveraging hybrid control modalities, researchers adiabatically introduced disorder to localize photons into a highly-entangled state resembling a cat state, and subsequently enhanced its coherence using a many-body echo technique. This innovative combination of techniques allows for the creation of unconventional quantum states where distinct phases of matter coexist. The platform utilizes a 1D Bose-Hubbard model implemented in a circuit of strongly interacting microwave photons confined to a lattice of coupled superconducting qubits. The system’s dynamics are governed by a Hamiltonian incorporating tunneling, on-site interactions, and site-dependent energy modulations controlled by the ancilla qubit. This precise control enables the creation of superpositions of solid (Mott insulator) and fluid eigenstates, entangled with the ancilla, and facilitates the exploration of long-range correlated states. Furthermore, the study introduces a many-body Ramsey interferometry technique to probe the coherence of these entangled states and an echo protocol to mitigate the effects of low-frequency phase noise. These advancements illustrate the potential for interfacing quantum computers with quantum matter, opening new avenues for sensing, materials characterization, and ultimately, achieving quantum advantage in complex computational tasks. Hamiltonian formulation and lattice potential modulation A 1D Bose-Hubbard model forms the foundation of this work, describing the coherent propagation of microwave photons within a lattice of coupled superconducting qubits. The Hamiltonian governing the system’s dynamics is expressed as HBH/ħ= J X ⟨i,j⟩ a† iaj + U 2X i ni (ni −1) + X i [ω0 + δi(t)]ni, where J represents the nearest-neighbor tunneling rate and U denotes the strength of local interactions. The operator a† i creates a microwave photon on site i, possessing an energy of ω0 +δi, and ħ is the reduced Planck’s constant. This superconducting circuit platform allows for precise control over the system’s parameters and photon dynamics. Researchers implemented a technique to entangle the lattice potential landscape with an ancilla qubit, enabling Hamiltonian-level quantum control of the many-body system. This was achieved by modulating the energy at each lattice site, δi(t), with qubit control, effectively creating a superposition of different lattice configurations dependent on the ancilla’s state. Consequently, the system evolved under these entangled configurations, realizing a photonic transistor where quantum logic is embedded within the analog dynamics of the many-body system. Following state preparation, the team adiabatically introduced site-resolved disorder to localize the photons into a highly-entangled N00N state, also known as a cat state. Ramsey measurements performed on the ancilla qubit were then used to assess the impact of the lattice geometry on the resulting many-body states. To further enhance coherence, a many-body echo technique was employed, decoupling the evolution of the entangled states from low-frequency phase noise. This protocol leverages the hybrid analog-digital control to suppress dephasing and maintain the integrity of the quantum information. The experimental setup utilizes a platform consisting of seven superconducting qubits, designated Q0 through Q6, configured to simulate the Bose-Hubbard model. Classical control signals modulate the energy δj at each site, while quantum control is applied via the ancilla qubit to manipulate the lattice potential and induce the desired dynamics. This precise control over both classical and quantum parameters is central to achieving the observed superposition of solid and fluid eigenstates. Collective phase shifts confirm N00N state assembly and adiabaticity criteria Fringe frequency enhancement of 5x was achieved through collective enhancement of the acquired phase, ∆φ = (N −1)δ∆t. This measurement was performed on lattices containing both N = 5 and N = 7 qubits, demonstrating a clear collective shift of (N −1)δ in the many-body Ramsey fringe frequency in response to applied lattice perturbation. The observation of this shift serves as a definitive signature of assembling the entangled N00N state. Adiabatic ramp rates were identified by monitoring the Fourier spectrum of the ancilla Ramsey fringes as a function of ramp duration, tramp. Driving the lattice site at ωd ≈3.6J induced a two-phonon process, inverting the population of free fermion eigenstates and enabling a multi-qubit SWAP operation. This process simultaneously exchanged photons between the highest frequency qubits (Q2, Q3) and the lowest frequency qubits (Q5, Q6), while leaving the solid state unaffected. The resulting many-body Rabi experiment confirmed a cyclic transition from the product state to the entangled cat state, demonstrating the successful implementation of the ancilla-conditioned SWAP operation. Coherent photon entanglement via digitally-guided analogue material evolution Scientists have successfully merged digital quantum control with the analog evolution of a synthetic quantum material, creating a hybrid platform with potential for advanced applications. This integration was achieved by entangling a Bose-Hubbard circuit’s lattice potential with an ancilla qubit, inducing dynamics under a superposition of lattice configurations and guiding the system towards novel strongly-correlated states exhibiting coexisting phases of matter. The resulting system allows for the creation of superpositions of solid and fluid eigenstates of photons, demonstrating a new method for manipulating many-body systems. This work demonstrates the ability to control and characterize complex quantum states by leveraging the strengths of both analog and digital quantum systems. Specifically, researchers adiabatically introduced disorder to localize photons into an entangled state and subsequently enhanced its coherence using a many-body echo technique. Error rates of 5.4% and 4.7% were measured for five- and seven-qubit entangled states, closely matching the limits imposed by single-qubit decoherence. The authors acknowledge that these error rates are currently constrained by the coherence of individual qubits within the system. Future research may focus on expanding the control register to improve the sensitivity and dynamic range of many-body sensors by embedding quantum Fourier transforms into the entangling dynamics. Further generalizations of the echo-based dynamical decoupling scheme, combined with multi-qubit operations, could lead to new quantum signal processing algorithms. This approach also offers a pathway to measure the entanglement spectrum of many-body states using Ramsey spectroscopy with a single control qubit, ultimately demonstrating a powerful synergy between analog quantum materials and small quantum computers for efficient materials characterization and sensing. 👉 More information 🗞 Quantum-controlled synthetic materials 🧠 ArXiv: https://arxiv.org/abs/2602.06108 Tags: