Quantum Information

I will talk about the applicability of a new kind of gas sensor based on Rydberg excitations. From a gas mixture the molecule in question is excited to a Rydberg state. By succeeding collisions with all other gas components this molecule ionizes and the emerging electrons can be measured as a current. I will show Doppler-free spectra for the A <- X transition, an estimate of the excitation efficiency dependent on the used laser powers, the applied charge-extraction voltage as well as the overall gas pressure and a first Stark map of NO Rydberg states recorded with cw excitation.

Electric field sensors based on warm vapors of Rydberg atoms have distinguishing features that offer new application possibilities. A single sensor can operate over a wide spectrum of frequencies, from DC to THz, with a consistent instantaneous baseband bandwidth of approximately 10MHz. The sensor head containing the vapor is highly transparent and can be made small relative to the electric field wavelengths, enabling accurate measurements with sub-wavelength spatial resolution. Presently Rydberg sensors rely on the spectroscopic method of electromagnetically induced transparency (EIT) for preparing and probing the atoms, and though simple and effective, this places limits on the sensitivity and instantaneous bandwidth of the sensor. I will discuss these limitations and the optimal EIT parameter regime considering presently available laser technology, and show performance of a promising new prototype vertical external cavity surface emitting laser (VECSEL). Finally, I will present results on recent demonstrations, such as a Rydberg-based spectrum analyzer with sensitivity of -145dBm/Hz and dynamic range >80 dB.

The strong interaction of optically excited Rydberg atoms with external fields has made them promising for the detection of radio frequency (RF) electric fields with high sensitivity. Such Rydberg-atom based sensors offer advantages over conventional metal antennas in RF transparency and self-calibration, enabled by all-dielectric construction and extremely well-known atomic properties. In this talk, we describe recent advances in the sensing of low amplitude RF electric fields and the timing of sub-microsecond RF pulses using room temperature Cesium vapour cells. We examine their transient response to RF pulses with durations ranging from 10 μs to 50 ns, identifying the dependence of atomic time scales on Rabi frequencies and dephasing mechanisms. We present a method for extracting the arrival time of RF pulses in a typical two-photon setup using a matched filter tailored to the atomic response, achieving a field sensitivity down to ~240 nV cm-1 Hz-1/2 and a timing precision of ~30 ns. On the other hand, practical operation at room temperature results in the self-calibration and sensitivity of this setup being limited by residual Doppler broadening. We therefore develop a novel sub-Doppler approach using a colinear three-photon scheme, which extends the self-calibrated Autler-Townes regime to significantly weaker RF electric fields. With this setup, we achieve a ~200 kHz spectral linewidth of the Rydberg atoms’ electromagnetically induced transparency within a room temperature vapour cell. The results demonstrate the potential of Rydberg atombased sensors for use in test and measurement, communications, and radar applications. "

"Neutral atoms have emerged as a competitive platform for digital quantum simulations and computing. In this talk, we discuss recent results on the design of time-optimal two- and three-qubit gates for neutral atoms, where entangling gates are implemented via the strong and long-range interactions provided by highly excited Rydberg states. We combine numerical and semi-analytical quantum optimal control techniques to obtain theoretically laser pulses that are “smooth”, time-optimal and “global” -- that is, they do not require individual addressability of the atoms. This technique improves upon current implementations of the controlled-Z (CZ) and the three-qubit C2Z gates with just a limited set of variational parameters, demonstrating the potential of quantum optimal control techniques for advancing quantum computing with Rydberg atoms."

"Neutral atom quantum computers with Rydberg mediated entangling gates are rapidly advancing as a leading platform for quantum information processing. I will present recent results running quantum algorithms for preparation of multi-qubit GHZ states, phase estimation, and hybrid quantum/classical optimization. Future fault tolerant quantum processors will require large numbers of qubits, high fidelity gates, and error correcting protocols. Work in progress towards fault tolerance including preparation of arrays of more than 1000 atoms, mid-circuit measurements, and multi-qubit gates will be presented"

"Rydberg atoms in arrays of optical tweezers offer a new perspective for the quantum simulation of many body systems. In this talk, I will give a brief overview about this platform and describe our efforts to control Rydberg interactions to explore different types of Hamiltonians. Through recent experimental results, I will illustrate the implementation of the Ising [1] and XXZ [2] Hamiltonians to study quantum magnetism. Finally, I will show our first steps to scale up the atom numbers in our platform by using a cryogenic environment [3]. References: [1] P. Scholl et al., Nature 595, 233 (2021). [2] P. Scholl et al., PRX Quantum 3, 020303 (2022). [3] K.N. Schymik et al., Phys. Rev. Applied 16, 034013 (2021)."

We will discuss the recent advances involving programmable, coherent manipulation of quantum many-body systems using neutral atom arrays excited into Rydberg states, allowing the control over 200 qubits in two dimensions. These systems can be used for realization and probing of exotic quantum phases of matter and exploration of their non-equilibrium dynamics. Recent advances involving the realization and probing of quantum spin liquid states - the exotic topological states of matter have thus far evaded direct experimental detection and the observation of quantum speedup for solving optimization problems will be described. In addition, the realization of novel quantum processing architecture based on dynamically reconfigurable entanglement and the steps towards quantum error correction will be discussed. Finally, we will discuss prospects for using these techniques for realization of large-scale quantum processors.

Atoms separated by distances comparable to or less than the wavelength of a photon for a dipole allowed transition can manifest collective effects. These effects can be apparent in the radiative lifetime of an excited state, how the atoms recoil when a photon is emitted, the transmission/reflectivity of an atomic cloud, etc. This talk will describe some of these processes and the theoretical machinery used to model them. This work is supported by the National Science Foundation under Award No. 2109987-PHY.

"133Cs as a low-frequency RF field sensor Seth T. Rittenhouse,1 Seth Meiselman,2 Vanessa Ortiz,1 and Geoffrey A. Cranch2 1Department of Physics, the United States Naval Academy, Annapolis, MD 21402, USA 2Optical Sciences Division, U. S. Naval Research Laboratory, Washington, DC 20375, USA Do to the extreme sensitivity of Rydberg systems to external fields, there has been a great deal of interest in using them as high precision quantum mechanical sensors. However, for intermediate principle quantum numbers (n ∼ 20 − 40), using the AC Stark effect to measure the intensity ofan RF field is limited to amplitudes on the order of ERF ∼ 1 V/cm. In this poster we examine the feasibility of using 133Cs as a high precision, low frequency (10-100 MHz) RF field sensor. We propose using a DC field offset to increase the field sensitivity of the AC Stark spectrum to the intensity of the RF field. The presence of the DC offset field leads to sideband states with Rabbi frequencies that are highly sensitive to RF field intensity. Using electromagnetically induced transpareny, our initial theoretical modeling indicates that this approach might be used to create a RF field sensor with sub-millivolt per centimeter accuracy."

Naomy Duarte Gomes1, Barbara da Fonseca Magnani1, Jorge Douglas Massayuki Kondo2, Luis Gustavo Marcassa1 1 Instituto de Fısica de Sao Carlos, Universidade de Sao Paulo 2 Departamento de Fısica, Universidade Federal de Santa Catarina In this work, we investigate the narrowing of the electromagnetically induced transparency (EIT) profile in a three-level ladder of rubidium atoms at room temperature using a Rydberg state and a Laguerre-Gaussian mode laser. The Gaussian probe field couples the 5S1/2 → 5P3/2 states. The control field, which can be in either Gaussian or Laguerre-Gaussian (LG) modes, couples the 5P3/2 → 44D state. The EIT spectrum is measured with the polarization spectroscopy (PS) technique, resulting in a dispersive signal. The dispersive PS EIT linewidth is 20% narrower for the LG mode than for a Gaussian mode, due to the donut spatial distribution of the LG mode used. We have implemented a probe transmission model using a simplified Lindblad master equation, which allows us to calculate the PS signal and reproduces well the experimental results. The use of the PS signal eliminates the need to fit a curve when measuring EIT linewidths while still providing subnatural widths. Narrowing the transmission profile is of great interest to measure effects such as atomic collisions and mi-crowave fields. *This work is supported by grants 2016/21311-2, 2019/10971-0 and 2021/06371-7, Sao Paulo Research Foundation (FAPESP) and grant 142410/2019-5, Brazilian National Council for Scientific and Technological Development (CNPq). It is also supported by grant (W911NF2110211) from the US Army.

In cold and ultracold mixtures of atoms and molecules, Rydberg interactions with surrounding atoms or molecules may, under certain conditions, lead to the formation of special long-range Rydberg molecules [1,2,3]. These exotic molecules provide an excellent toolkit for manipulation and control of interatomic and atom-molecule interactions, with applications in ultracold chemistry, quantum information processing and many-body quantum physics. In this talk, we will discuss ultralong-range polyatomic Rydberg molecules formed when a heteronuclear diatomic molecule is bound to a Rydberg atom [3,4]. The binding mechanism appears due to anisotropic scattering of the Rydberg electron from the permanent electric dipole moment of the polar molecule. We propose an experimentally realizable scheme to produce these triatomic ultralong-range Rydberg molecules in ultracold RbCs traps, which might use the excitation of cesium or rubidium [5]. By exploiting the Rydberg electron-molecule anisotropic dipole interaction, we induce a near resonant coupling of the non-zero quantum defect Rydberg levels with the RbCs molecule in an excited rotational level. This coupling enhances the binding of the triatomic ultralong-range Rydberg molecule and produces favorable Franck-Condon factors. References [1] C. H. Greene, A. S. Dickinson, and H. R. Sadeghpour, Phys. Rev. Lett. 85, 2458 (2000). [2] S. T. Rittenhouse and H. R. Sadeghpour, Phys. Rev. Lett. 104, 243002 (2010). [3] V. Bendkowsky, B. Butscher, J. Nipper, J. P. Shaffer, R. Löw, and T. Pfau, Nature 458, 1005 (2009). [4] R. González-Férez, H. R. Sadeghpour, and P. Schmelcher, New J. Phys. 17, 013021 (2015). [5] R. González-Férez, S.T. Rittenhouse, P. Schmelcher and H.R. Sadeghpour, J. Phys. B 53, 074002 (2020)."