arXiv subjects

Lewis R. B. Picard

Publications and source records attributed to Lewis R. B. Picard.

14 recordsLinked to original sources

arXiv2026

Shor's algorithm is possible with as few as 10,000 reconfigurable atomic qubits

Quantum computers have the potential to perform computational tasks beyond the reach of classical machines. A prominent example is Shor's algorithm for integer factorization and discrete logarithms, which is of both fundamental importance and practical relevance to cryptography. However, due to the high overhead of quantum error correction, optimized resource estimates for cryptographically relevant instances of Shor's algorithm require millions of physical qubits. Here, by leveraging advances in high-rate quantum error-correcting codes, efficient logical instruction sets, and circuit design, we show that Shor's algorithm can be executed at cryptographically relevant scales with as few as 10,000 reconfigurable atomic qubits. Increasing the number of physical qubits improves time efficiency by enabling greater parallelism; under plausible assumptions, the runtime for discrete logarithms on the P-256 elliptic curve could be just a few days for a system with 26,000 physical qubits, while the runtime for factoring RSA-2048 integers is one to two orders of magnitude longer. Recent neutral-atom experiments have demonstrated universal fault-tolerant operations below the error-correction threshold, computation on arrays of hundreds of qubits, and trapping arrays with more than 6,000 highly coherent qubits. Although substantial engineering challenges remain, our theoretical analysis indicates that an appropriately designed neutral-atom architecture could support quantum computation at cryptographically relevant scales. More broadly, these results highlight the capability of neutral atoms for fault-tolerant quantum computing with wide-ranging scientific and technological applications.

quant-ph↗

arXiv2026

Gate-based Readout and Cooling of Neutral Atoms

Neutral atom arrays have seen tremendous progress in quantum simulation, quantum metrology, and fault-tolerant quantum computing. However, hardware constraints such as atom loss and heating remain significant challenges. In this work, we introduce a comprehensive ancilla-based toolbox for optical tweezer experiments that utilizes high-fidelity Rydberg entangling gates and ancilla atoms to mitigate these physical limitations. First, we demonstrate repeated ancilla-based atom readout, achieving improved detection fidelity over multiple rounds with minimal perturbation to data atoms. Second, leveraging the quantized motional states in tweezer-trapped strontium atoms, we transduce quantum information from the electronic to the motional manifold. This enables us to perform mid-circuit ancilla-based atom loss detection in a coherence-preserving fashion. Finally, we demonstrate algorithmic cooling, a circuit-based sequence that deterministically cools data atoms by transferring their motional entropy to the electronic states of ancilla atoms. We observe a marked reduction in the atomic temperature of data atoms. These tools offer a pathway to continuous operation in tweezer clocks and complement recent developments in continuous reloading experiments.

quant-ph↗

arXiv2026

Experimental observation of conformal field theory spectra

Conformal field theories (CFTs) feature prominently in high-energy physics, statistical mechanics, and condensed matter. For example, CFTs govern emergent universal properties of systems tuned to quantum phase transitions, including their entanglement, correlations, and low-energy excitation spectra. Much of the rich structure predicted by CFTs nevertheless remains unobserved in experiment. Here we directly observe the energy excitation spectra of emergent CFTs at quantum phase transitions -- recovering universal energy ratios characteristic of the underlying field theories. Specifically, we develop and implement a modulation technique to resolve a Rydberg chain's finite-size spectra, variably tuned to quantum phase transitions described by either Ising or tricritical Ising CFTs. We also employ local control to distinguish parities of excitations under reflection and, in the tricritical Ising chain, to induce transitions between distinct CFT spectra associated with changing boundary conditions. By utilizing a variant of the modulation technique, we furthermore study the dynamical structure factor of the critical system, which is closely related to the correlation of an underlying Ising conformal field. Our work not only probes the emergence of CFT features in a quantum simulator, but also provides a technique for diagnosing a priori unknown universality classes in future experiments.

quant-ph↗

arXiv2025

A three-dimensional acousto-optic deflector

Acousto-optic deflectors (AODs) are widely used across physics, microscopy, neuroscience, and laser engineering, providing fast, precise, and non-mechanical control of light. While conventional AODs naturally support multiplexing in one and two dimensions, no analogous device has existed for three-dimensional control, leaving a critical gap in rapid focus tuning and 3D beam shaping. Here we demonstrate a three-dimensional AOD system capable of multiplexed axial and lateral beam control with high speed and large dynamic range. We achieve this by combining a double-pass AOD with a diffraction grating in the Littrow configuration to realize a compact frequency-tunable lens with multiplexing capability. Our device enables axial scanning over more than twenty Rayleigh ranges with switching rates up to 100 kHz, while simultaneous multi-tone driving produces arbitrary multi-focal beam profiles. By integrating the axial module with lateral deflection, we generate reconfigurable 3D optical patterns. This approach establishes a broadly applicable platform for multiplexed 3D beam control, with potential applications from high-resolution microscopy and laser processing to scalable neutral-atom quantum technologies.

physics.optics↗

arXiv2024

Sub-millisecond Entanglement and iSWAP Gate between Molecular Qubits

Quantum computation (QC) and simulation rely on long-lived qubits with controllable interactions. Early work in quantum computing made use of molecules because of their readily available intramolecular nuclear spin coupling and chemical shifts, along with mature nuclear magnetic resonance techniques. Subsequently, the pursuit of many physical platforms has flourished. Trapped polar molecules have been proposed as a promising quantum computing platform, offering scalability and single-particle addressability while still leveraging inherent complexity and strong couplings of molecules. Recent progress in the single quantum state preparation and coherence of the hyperfine-rotational states of individually trapped molecules allows them to serve as promising qubits, with intermolecular dipolar interactions creating entanglement. However, universal two-qubit gates have not been demonstrated with molecules. Here, we harness intrinsic molecular resources to implement a two-qubit iSWAP gate using individually trapped $X^{1}Σ^{+}$ NaCs molecules. We characterize the innate dipolar interaction between rotational states and control its strength by tuning the polarization of the traps. By allowing the molecules to interact for 664 $μ$s at a distance of 1.9 $μ$m, we create a maximally entangled Bell state with a fidelity of 94(3)\%, following postselection to remove trials with empty traps. Using motion-rotation coupling, we measure residual excitation of the lowest few motional states along the axial trapping direction and find them to be the primary source of decoherence. Finally, we identify two non-interacting hyperfine states within the ground rotational level in which we encode a qubit. The interaction is toggled by transferring between interacting and non-interacting states to realize an iSWAP gate. We verify the gate performance by measuring its logical truth table.

physics.atom-ph↗

arXiv2024

Site-selective preparation and multi-state readout of molecules in optical tweezers

Polar molecules are a quantum resource with rich internal structure that can be coherently controlled. The structure, however, also makes the state preparation and measurement (SPAM) of molecules challenging. We advance the SPAM of individual molecules assembled from constituent atoms trapped in optical tweezer arrays. Sites without NaCs molecules are eliminated using high-fidelity Cs atom detection, increasing the peak molecule filling fraction of the array threefold. We site-selectively initialize the array in a rotational qubit subspace that is insensitive to differential AC Stark shifts from the optical tweezer. Lastly, we detect multiple rotational states per experimental cycle by imaging atoms after sequential state-selective dissociations. These demonstrations extend the SPAM capabilities of molecules for quantum information, simulation, and metrology.

physics.atom-ph↗

arXiv2023

Extended rotational coherence of polar molecules in an elliptically polarized trap

We demonstrate long rotational coherence of individual polar molecules in the motional ground state of an optical trap. In the present, previously unexplored regime, the rotational eigenstates of molecules are dominantly quantized by trapping light rather than static fields, and the main source of decoherence is differential light shift. In an optical tweezer array of NaCs molecules, we achieve a three-orders-of-magnitude reduction in differential light shift by changing the trap's polarization from linear to a specific "magic" ellipticity. With spin-echo pulses, we measure a rotational coherence time of 62(3) ms (one pulse) and 250(40) ms (up to 72 pulses), surpassing the projected duration of resonant dipole-dipole entangling gates by orders of magnitude.

physics.atom-ph↗

arXiv2023

High resolution photoassociation spectroscopy of the excited $c^3Σ_{1}^+$ potential of $^{23}$Na$^{133}$Cs

We report on photoassociation spectroscopy probing the $c^3Σ_{1}^+$ potential of the bi-alkali NaCs molecule, identifying eleven vibrational lines between $v' = 0$ and $v' = 25$ of the excited $c^3Σ_{1}^+$ potential, and resolving their rotational and hyperfine structure. The observed lines are assigned by fitting to an effective Hamiltonian model of the excited state structure with rotational and hyperfine constants as free parameters. We discuss unexpected broadening of select vibrational lines, and its possible link to strong spin-orbit coupling of the $c^3Σ_{1}^+$ potential with the nearby $b^3Π_1$ and $B^1Π_1$ manifolds. Finally we report use of the $v' = 22$ line as an intermediate state for two-photon transfer of weakly bound Feshbach molecules to the rovibrational ground state of the $X^1Σ^+$ manifold.

physics.atom-ph↗

arXiv2022

Enriching the quantum toolbox of ultracold molecules with Rydberg atoms

We describe a quantum information architecture consisting of a hybrid array of optically-trapped molecules and atoms. This design leverages the large transition dipole moments of Rydberg atoms to mediate fast, high-fidelity gates between qubits encoded in coherent molecular degrees of freedom. Error channels of detuning, decay, pulse area noise, and leakage to other molecular states are discussed. The molecule-Rydberg interaction can also be used to enable nondestructive molecule detection and rotational state readout. We consider a specific near-term implementation of this scheme using NaCs molecules and Cs Rydberg atoms, showing that it is possible to implement 300~ns gates with a potential fidelity of $> 99.9\%$.

physics.atom-ph↗

arXiv2021

An optical tweezer array of ground-state polar molecules

Fully internal and motional state controlled and individually manipulable polar molecules are desirable for many quantum science applications leveraging the rich state space and intrinsic interactions of molecules. While prior efforts at assembling molecules from their constituent atoms individually trapped in optical tweezers achieved such a goal for exactly one molecule, here we extend the technique to an array of five molecules, unlocking the ability to study molecular interactions. We detail the technical challenges and solutions inherent in scaling this system up. With parallel preparation and control of multiple molecules in hand, this platform now serves as a starting point to harness the vast resources and long-range dipolar interactions of molecules.

physics.atom-ph↗

arXiv2021

Assembly of a rovibrational ground state molecule in an optical tweezer

We demonstrate the coherent creation of a single NaCs molecule in its rotational, vibrational, and electronic (rovibronic) ground state in an optical tweezer. Starting with a weakly bound Feshbach molecule, we locate a two-photon transition via the $|{c^3Σ,v'=26}\rangle$ excited state and drive coherent Rabi oscillations between the Feshbach state and a single hyperfine level of the NaCs rovibronic ground state $|{X^1Σ,v''=0,N''=0}\rangle$ with a binding energy of $D_0 = h \times 147038.30(2)$ GHz. We measure a lifetime of $3.4\pm1.6$ s for the rovibronic ground-state molecule, which possesses a large molecule-frame dipole moment of 4.6 Debye and occupies predominantly the motional ground state. These long-lived, fully quantum-state-controlled individual dipolar molecules provide a key resource for molecule-based quantum simulation and information processing.

physics.atom-ph↗

arXiv2020

Coherent optical creation of a single molecule

We report coherent association of atoms into a single weakly bound NaCs molecule in an optical tweezer through an optical Raman transition. The Raman technique uses a deeply bound electronic excited intermediate state to achieve a large transition dipole moment while reducing photon scattering. Starting from two atoms in their relative motional ground state, we achieve an optical transfer efficiency of 69%. The molecules have a binding energy of 770.2MHz at 8.83(2)G. This technique does not rely on Feshbach resonances or narrow excited-state lines and may allow a wide range of molecular species to be assembled atom-by-atom.

physics.atom-ph↗

arXiv2020

Forming a single molecule by magnetoassociation in an optical tweezer

We demonstrate the formation of a single NaCs molecule in an optical tweezer by magnetoassociation through an s-wave Feshbach resonance at 864.11(5)G. Starting from single atoms cooled to their motional ground states, we achieve conversion efficiencies of 47(1)%, and measure a molecular lifetime of 4.7(7)ms. By construction, the single molecules are predominantly (77(5)%) in the center-of-mass motional ground state of the tweezer. Furthermore, we produce a single p-wave molecule near 807G by first preparing one of the atoms with one quantum of motional excitation. Our creation of a single weakly bound molecule in a designated internal state in the motional ground state of an optical tweezer is a crucial step towards coherent control of single molecules in optical tweezer arrays.

physics.atom-ph↗

arXiv2019

Deep Learning-Assisted Classification of Site-Resolved Quantum Gas Microscope Images

We present a novel method for the analysis of quantum gas microscope images, which uses deep learning to improve the fidelity with which lattice sites can be classified as occupied or unoccupied. Our method is especially suited to addressing the case of imaging without continuous cooling, in which the accuracy of existing threshold-based reconstruction methods is limited by atom motion and low photon counts. We devise two neural network architectures which are both able to improve upon the fidelity of threshold-based methods, following training on large data sets of simulated images. We evaluate these methods on simulations of a free-space erbium quantum gas microscope, and a noncooled ytterbium microscope in which atoms are pinned in a deep lattice during imaging. In some conditions we see reductions of up to a factor of two in the reconstruction error rate, representing a significant step forward in our efforts to implement high fidelity noncooled site-resolved imaging.

cond-mat.quant-gas↗