Cornelius Hempel

Last Name

Hempel

First Name

Cornelius

ORCID

0000-0002-4053-722X

Organisational unit

03892 - Home, Jonathan / Home, Jonathan

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Publications 1 - 6 of 6

Laser-Written Waveguide Array Optimized for Individual Control of Trapped Ion Qubits in a Chain
Timpu, Flavia; Matt, Roland; Piacentini, Simone; et al. (2022)
OSA Technical Digest ~ European Conference on Optical Communication (ECOC) 2022
We design and fabricate a waveguide array with custom mode size and pitch. We measure crosstalk values below -45 dB within the array and Gaussian emission profiles. This device enhances the performance of parallel addressing of individual ions compared to state-of-the-art methods using beam deflectors.
Direct observation of geometric-phase interference in dynamics around a conical intersection
Valahu, Christophe H.; Olaya-Agudelo, Vanessa Carolina; MacDonell, Ryan J.; et al. (2023)
Nature Chemistry
Conical intersections are ubiquitous in chemistry and physics, often governing processes such as light harvesting, vision, photocatalysis and chemical reactivity. They act as funnels between electronic states of molecules, allowing rapid and efficient relaxation during chemical dynamics. In addition, when a reaction path encircles a conical intersection, the molecular wavefunction experiences a geometric phase, which can affect the outcome of the reaction through quantum-mechanical interference. Past experiments have measured indirect signatures of geometric phases in scattering patterns and spectroscopic observables, but there has been no direct observation of the underlying wavepacket interference. Here we experimentally observe geometric-phase interference in the dynamics of a wavepacket travelling around an engineered conical intersection in a programmable trapped-ion quantum simulator. To achieve this, we develop a technique to reconstruct the two-dimensional wavepacket densities of a trapped ion. Experiments agree with the theoretical model, demonstrating the ability of analogue quantum simulators—such as those realized using trapped ions—to accurately describe nuclear quantum effects. [Figure not available: see fulltext.].
Experimental Quantum Simulation of Chemical Dynamics
Navickas, Tomas; MacDonell, Ryan J.; Valahu, Christophe H.; et al. (2025)
Journal of the American Chemical Society
Accurate simulation of dynamic processes in molecules and reactions is among the most challenging problems in quantum chemistry. Quantum computers promise efficient chemical simulation, but the existing quantum algorithms require many logical qubits and gates, placing practical applications beyond existing technology. Here, we carry out the first quantum simulations of chemical dynamics by employing a more hardware-efficient encoding scheme that uses both qubits and bosonic degrees of freedom. Our trapped-ion device accurately simulates the dynamics of nonadiabatic chemical processes, which are among the most difficult problems in computational chemistry because they involve strong coupling between electronic and nuclear motions. We demonstrate the programmability and versatility of our approach by simulating the dynamics of three different molecules, as well as open-system dynamics in the condensed phase, all with the same quantum resources. Our approach requires orders of magnitude fewer resources than equivalent qubit-only quantum simulations, demonstrating the potential of using hybrid encoding schemes to accelerate quantum simulations of complex chemical processes, which could have applications in fields ranging from energy conversion and storage to biology and drug design.
Active stabilization of laser diode injection using a polarization-spectroscopy technique
Milanovic, Luka; Ferrero, Greg; Oswald, Robin; et al. (2025)
Review of Scientific Instruments
Laser diode injection-locking is a commonly used method to amplify laser light, while preserving its spectral properties. Fluctuations in the environmental conditions can cause injection-locking to fail, especially when operating with low seed powers or with a swept seed frequency. We present a method inspired by the Hänsch-Couillaud scheme to monitor and actively stabilize the conditions required for injection-locking a laser diode. Using only a few optical components, our scheme can run continuously in the background and is modulation-free. We demonstrate its efficacy by showing its robustness to large fluctuations in diode temperature, seed frequency and power, effectively extending the reliable operating range and stability over time.
Two qubits for the price of one ion
Hempel, Cornelius (2022)
Nature Physics
Predicting molecular vibronic spectra using time-domain analog quantum simulation
MacDonell, Ryan J.; Navickas, Tomas; Wohlers-Reichel, Tim F.; et al. (2023)
Chemical Science
Spectroscopy is one of the most accurate probes of the molecular world. However, predicting molecular spectra accurately is computationally difficult because of the presence of entanglement between electronic and nuclear degrees of freedom. Although quantum computers promise to reduce this computational cost, existing quantum approaches rely on combining signals from individual eigenstates, an approach whose cost grows exponentially with molecule size. Here, we introduce a method for scalable analog quantum simulation of molecular spectroscopy: by performing simulations in the time domain, the number of required measurements depends on the desired spectral range and resolution, not molecular size. Our approach can treat more complicated molecular models than previous ones, requires fewer approximations, and can be extended to open quantum systems with minimal overhead. We present a direct mapping of the underlying problem of time-domain simulation of molecular spectra to the degrees of freedom and control fields available in a trapped-ion quantum simulator. We experimentally demonstrate our algorithm on a trapped-ion device, exploiting both intrinsic electronic and motional degrees of freedom, showing excellent quantitative agreement for a single-mode vibronic photoelectron spectrum of SO₂.

Publications 1 - 6 of 6

Cornelius Hempel

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