Research Interests

Graduate Research

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Quantum Movies

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Quantum Simulator and Computer Projects

For the most part, we do not directly perform calculations of quantum simulators or computers in the sense of creating or investigating algorithms, testing various protocols, etc. Our main interest is in studying the physics of the different parts of quantum simulator or computer platforms with a concentration on effects that are typically left out of the idealized studies. We also develop the physics of the components of different platforms so that quantitatively accurate interactions within a quantum simulator or computer can be predicted.

Below is a brief description of results in two recent publications. These investigations are good examples of our interests. The first highlights the role that recoil of atoms when a single photon interacts with an array can be substantially more problematic than expected. The second investigates the infidelity on a particular kind of gate due to many different experimental parameters.

Deepak A. Suresh and F. Robicheaux, “Photon-induced atom recoil in collectively interacting planar arrays,” Phys. Rev. A 103, 043722 (2021). PDF (655 kB) (data for figures at https://doi.org/10.4231/HHNZ-SP39)

In this paper, we studied how atoms in an array recoil due to the emission or absorption of a photon. This is an important question because an atom that recoils can have its center-of-mass motion entangle with internal degrees of freedom which leads to unwanted decoherence in the operation of quantum simulators or computers. This is not a simple question because a photon can distribute the recoil over many atoms. We also found cases where a single photon could lead to 1000X the expected recoil energy deposited into a single atom. Also, the interference between the incident and scattered photon field can lead to nontrivial patterns of energy deposition in the array.

The left image shows the electric field for a proposed cavity composed of atoms on a grid; the bright spots are the positions of the atoms which enhance the intensity in their neighborhood. The proposal did not account for the possible recoil of the atoms in the array. The right image shows the recoil energy for an example cavity. Note that the center atom gains approximately 1000 recoil energies before the photon is lost from the cavity. This high recoil results from the photon bouncing many times between the mirrors constructed from the atom arrays.

These images are for light perpendicularly incident on an 11X11 array of atoms. The left plot shows the probability for each atom in the array to be excited by the photon. The right plot shows the amount of recoil energy deposited into each atom per photon incident on that atom. Although each photon can only interact once with the array, many of the atoms gain more than 2 recoil energies. Also, there is a highly nontrivial pattern of energy deposition which roughly matches the pattern of excitation of the array.

F. Robicheaux, T.M. Graham, and M. Saffman, “Photon-recoil and laser-focusing limits to Rydberg gate fidelity,” Phys. Rev. A 103, 022424 (2021). PDF (642 kB) (data for figures at https://doi.org/10.4231/B7CM-VP26)

In this paper, we study several mechanisms that can decrease the fidelity of a two atom gate that uses the Rydberg-Rydberg interaction to entangle hyperfine states of a pair of atoms (see below). In particular, we quantitatively study effects that lead to infidelities from less than 0.0001 to 0.01. Examples of the processes we study include: photon kick from a pair of counter-propagating laser pulses, photon kick due to focussing of the light beam, residual kick from the Rydberg-Rydberg interaction, etc.

This image is a cartoon of the type of gate investigated in this paper. This is a gate that uses the Rydberg-Rydberg interaction between highly excited atoms to entangle the hyperfine states being used as qubits. By having many atoms in an array of optical traps, a quantum simulator or computer can be constructed with this being the main 2-qubit entangling gate.

Five Recent Publications

A. Trautmann, M. J. Mark, P. IlzhŲfer, H. Edri, A. El Arrach, J. G. Maloberti, C. H. Greene, F. Robicheaux, and F. Ferlaino, “Spectroscopy of Rydberg states in erbium using electromagnetically induced transparency,” Phys. Rev. Res. 3, 033165 (2021). PDF (1750 kB) (MQDT data at https://doi.org/10.4231/HK40-XM43)

F. Robicheaux, “Calculations of long range interactions for 87Sr Rydberg states,” J. Phys. B 52, 244001 (2019). PDF (489 kB)

F. Robicheaux and Shihua Huang, "Atom recoil during coherent light scattering from many atoms," Phys. Rev. A 99, 013410 (2019). PDF (603 kB)

F. Robicheaux, D.W. Booth, and M. Saffman, "Theory of long-range interactions for Rydberg states attached to hyperfine-split cores," Phys. Rev. A 97, 022508 (2018). PDF (678 kB)

M.T. Eiles, J. Perez-Rios, F. Robicheaux and C.H. Greene, "Ultracold molecular Rydberg physics in a high density environment," J. Phys. B 49, 114005 (2016). PDF (2010 kB)

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284 Physics Building (Office)
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Department of Physics
525 Northwestern Avenue
West Lafayette, IN 47907


Phyics Department

Purdue University

ALPHA Project