arXiv subjects

Lukas Novotny

Publications and source records attributed to Lukas Novotny.

At least 19 recordsLinked to original sources

arXiv2026

Single-atom detection with a quantum-controlled mechanical oscillator

Using supersonic expansion, we create a time-gated, directional beam of Xe atoms with a narrow momentum distribution and detect their collisions with a levitated nanosphere cooled to its quantum ground state. We observe individual momentum kicks below 50 keV/c with 96% confidence and distinguish directional momentum transfer from the atomic beam against the background of thermal collisions. Our experiments constitute a first step toward the exploration of distance-dependent short-range interactions between atoms and levitated systems, as well as toward the use of levitated platforms for impulsive force sensing in previously unexplored parameter regimes.

quant-ph↗

arXiv2026

Shot-to-shot noise cancellation for parametric oscillators

Powerful approaches to squeeze the motional state of a harmonic oscillator rely on the stepwise modulation of its resonance frequency. Such protocols can be limited by forces that vary slowly between experimental runs but are constant during a single experimental shot. Such shot-to-shot noise gives rise to a spread in experimental outcomes that masks the uncertainty intrinsic to quantum theory. Taking inspiration from spin-echo protocols, we propose a decoupling technique that, under ideal conditions, perfectly cancels shot-to-shot force noise in squeezing experiments based on parametric modulation. We implement the protocol using an optically levitated nanoparticle, where shot-to-shot force noise arises from slowly varying stray fields acting on the charge carried by the particle. Using our oscillator-echo protocol, we demonstrate shot-to-shot noise suppression to the measurement-backaction limit.

quant-ph↗

arXiv2026

Nanomechanical sensor resolving impulsive forces below its zero-point fluctuations

The sensitivity of a mechanical transducer is ultimately limited by its inherent quantum fluctuations. Here, we use an optically levitated nanoparticle to measure impulsive forces smaller than the particle's zero-point momentum uncertainty. Our approach relies on reversibly squeezing the levitated particle's center-of-mass motion to coherently amplify the perturbation. We demonstrate resolving single impulsive-force kicks as small as 6.9 keV/c, a value 0.6 dB below the sensor's zero-point value.

quant-ph↗

arXiv2025

Shot-to-shot displacement noise in state-expansion protocols with inverted potentials

Optically levitated nanoparticles are promising candidates for the generation of macroscopic quantum states of mechanical motion. Protocols to generate such states expose the particle to a succession of different potentials. Limited reproducibility of the alignment of these potentials across experimental realizations introduces additional noise. Here, we experimentally investigate and model how such shot-to-shot noise limits the coherence length of a levitated nanoparticle during a state-expansion protocol using a dark, inverted electrical potential. We identify electric stray fields and mechanical instabilities as major sources of shot-to-shot fluctuations. We discuss the resulting experimental requirements for state expansion protocols exploiting inverted potentials.

quant-ph↗

arXiv2025

Electrically driven plasmon-polaritonic bistability in Dirac electron tunneling transistors

Bistability-two distinct stable states under identical parameter-is not only a fundamental physical concept but also of importance in practical applications. While plasmon-polaritonic bistability representing history-dependent stable states within plasmonic systems has been theoretically predicted, it has yet to be demonstrated experimentally due to challenges in realizing suitable nonlinearity at feasible electric-field strengths. Here, we report the experimental observation of electrically driven plasmon-polaritonic bistability in graphene/hexagonal-boron-nitride/graphene tunneling transistors, achieved through momentum-conserving resonant tunneling of Dirac electrons. Using a small twist angle between graphene layers, we engineered devices exhibiting both electronic and plasmon-polaritonic bistability. This bistable plasmonic behavior can be precisely tuned through load resistance and electrostatic gating. Our findings open new pathways for exploring nonlinear optical and electronic phenomena in van der Waals heterostructures and mark a significant advance in nanoplasmonics, with potential applications in optical memory, sensing, and optoelectronic switching.

cond-mat.mes-hall↗

arXiv2025

Atomically-resolved exciton emission from single defects in MoS$_2$

Understanding how atomic defects shape the nanoscale optical properties of two-dimensional (2D) semiconductors is essential for advancing quantum technologies and optoelectronics. Using scanning tunneling spectroscopy (STS) and luminescence (STML), we correlate the atomic structure and optical fingerprints of individual defects in monolayer MoS$_2$. A bilayer of hexagonal boron nitride (hBN) effectively decouples MoS$_2$ from the graphene substrate, increasing its band gap and extending the defect charge state lifetime. This enables the observation of sharp STML emission lines from MoS$_2$ excitons and trions exhibiting nanoscale sensitivity to local potential fluctuations. We identify the optical signatures of common point defects in MoS$_2$: sulfur vacancies (Vac$_\text{S}^-$), oxygen substitutions (O$_\text{S}$), and negatively charged carbon-hydrogen complexes (CH$_\text{S}^-$). While Vac$_\text{S}^-$ and O$_\text{S}$ only suppress pristine excitonic emission, CH$_\text{S}^-$ generate defect-bound exciton complexes ($A^-X$) about 200\,meV below the MoS$_2$ exciton. Sub-nanometer-resolved STML maps reveal large spectral shifts near charged defects, concurrent with the local band bending expected for band-to-defect optical transitions. These results establish an atomically precise correlation between structure, electronic states, and optical response, enabling deterministic engineering of quantum emitters in 2D materials.

cond-mat.mtrl-sci↗

arXiv2025

Magnetic Chiral Light

We present a result derived from the optical chirality continuity equation that shows the existence of a source term describing optical chirality generation through the interactions of the magnetic induction field with a source current, without contributions from the electric field. This framework is validated through a metasurface-based methodology. Using a lossless, all-dielectric nanoparticle array, we engineer an in-plane rotating electric field that generates out-of-plane optical magnetism. This array exhibits a far-field circular dichroism of 0.47 and a high-quality factor on the order of 10^6. The presented findings demonstrate the feasibility of inducing chiral optical responses from a magnetic source. This work establishes a new paradigm for structured photonic media, offering insights into the design of nanophotonic devices that exploit optical magnetism for chiral light-matter interactions.

physics.optics↗

arXiv2025

Trap-to-trap free falls with an optically levitated nanoparticle

We perform free-fall experiments with a charge-neutral, optically levitated nanoparticle. This is achieved using an optical tweezer that can be rapidly toggled on and off and vertically displaced, enabling the particle to be released and recaptured after each free fall. The particle is insensitive to electric fields due to its charge neutrality and, during free evolution, is not subject to photon recoil heating. We achieve free-fall durations of up to 0.25 ms and observe a nearly two hundred-fold increase in the particle's position uncertainty at recapture. The current limit on the free-fall time arises from the performance of the initial cooling step. By implementing linear feedback techniques and reducing the background pressure, we expect to perform millisecond-scale free-fall experiments in ultra-high vacuum, opening new opportunities for generating large delocalizations of levitated objects.

quant-ph↗

arXiv2025

All-electrical near-field injection of excitons in a van der Waals antiferromagnet

Van der Waals materials have become a promising building block for future electronics and photonics. The two-dimensional magnet CrSBr came into the spotlight of solid state research due to its intriguing combination of antiferromagnetic order, strong light-matter coupling and unusual quasi-1D electronic bandstructure. This study reports the electrical excitation of excitons in CrSBr layers from cryogenic temperatures up to room temperature. By exploiting the energy transfer via tunneling electrons in a graphene tunnel junction strongly bound excitons are excited in proximate CrSBr layers. This facilitates electrically-excited emission from CrSBr crystals ranging in thickness from a bilayer up to 250 nm, in which the strong linear polarization of the electroluminescence confirms the excitonic origin. For thicker layers, clear evidence for the electrically excited emission from self-hybridized exciton polaritons is observed, highlighting the strong coupling between optical excitations and confined photon modes in CrSBr. These results pave the way for future applications in spintronic and optical readout of magnetic properties.

cond-mat.mes-hall↗

arXiv2024

High-purity quantum optomechanics at room temperature

Exploiting quantum effects of mechanical motion, such as backaction evading measurements or squeezing, requires preparation of the oscillator in a high-purity state. The largest state purities in optomechanics to date have relied on cryogenic cooling, combined with coupling to electromagnetic resonators driven with a coherent radiation field. In this work, we cool the mega-hertz-frequency librational mode of an optically levitated silica nanoparticle from room temperature to its quantum ground state. Cooling is realized by coherent scattering into a Fabry-Perot cavity. We use sideband thermometry to infer a phonon population of 0.04 quanta under optimal conditions, corresponding to a state purity of 92%. The purity reached by our room-temperature experiment exceeds the performance offered by mechanically clamped oscillators in a cryogenic environment. Our work establishes a platform for high-purity quantum optomechanics at room temperature.

quant-ph↗

arXiv2024

Motional entanglement of remote optically levitated nanoparticles

We show how to entangle the motion of optically levitated nanoparticles in distant optical tweezers. The scheme consists in coupling the inelastically scattered light of each particle into transmission lines and directing it towards the other particle. The interference between this light and the background field introduces an effective coupling between the two particles while simultaneously reducing the effect of recoil heating. We analyze the system dynamics, showing that both transient and conditional entanglement between remote particles can be achieved under realistic experimental conditions.

quant-ph↗

arXiv2024

Quantum Delocalization of a Levitated Nanoparticle

Every massive particle behaves like a wave, according to quantum physics. Yet, this characteristic wave nature has only been observed in double-slit experiments with microscopic systems, such as atoms and molecules. The key aspect is that the wavefunction describing the motion of these systems extends coherently over a distance comparable to the slit separation, much larger than the size of the system itself. Preparing these states of more massive and complex objects remains an outstanding challenge. While the motion of solid-state oscillators can now be controlled at the level of single quanta, their coherence length remains comparable to the zero-point motion, limited to subatomic distances. Here, we prepare a delocalized state of a levitating solid-state nanosphere with coherence length exceeding the zero-point motion. We first cool its motion to the ground state. Then, by modulating the stiffness of the confinement potential, we achieve more than a threefold increment of the initial coherence length with minimal added noise. Optical levitation gives us the necessary control over the confinement that other mechanical platforms lack. Our work is a stepping stone towards the generation of delocalization scales comparable to the object size, a crucial regime for macroscopic quantum experiments, and towards quantum-enhanced force sensing with levitated particles.

quant-ph↗

arXiv2024

Radiation damping of a Rayleigh scatterer illuminated by a plane wave

We investigate the radiation damping experienced by a dielectric spherical particle when it is illuminated by an electromagnetic plane wave within the Rayleigh regime. We derive the equivalent electric dipole of the moving particle and subsequently calculate the electromagnetic force acting on it from two different approaches. In the first approach, we calculate the force from the integration of stress tensor and field momentum. In the second one, we calculate the force directly from the integration of the force density. Our derivations reveal that the damping coefficient is equal to $6P_{scat}/mc^2$ along the propagation direction, whereas it is $P_{scat}/mc^2$ along perpendicular directions. Here, $P_{scat}$ denotes the power scattered by the particle, and $mc^2$ represents the particle's mass energy. The radiation damping derived in this study sets upper limits on the quality factor of optically levitated objects and ensures the existence of a steady-state solution of the particle's dynamics.

physics.optics↗

arXiv2024

Feedback cooling a levitated nanoparticle's libration to below 100 phonons

Macroscopic rotors are interesting model systems to test quantum theory and for quantum sensing. A promising approach for bringing these systems to the quantum regime is to combine sensitive detection with feedback cooling to reduce the thermal occupation of the mechanics. Here, we implement a backward-scattering scheme to efficiently detect all three libration modes of an optically levitated nanoparticle. We demonstrate parametric feedback cooling of all three libration degrees of freedom to below 16~mK, with one of the modes reaching the temperature of 1.3~mK, corresponding to a mean phonon number of 84. Finally, we characterize the backward-scattering scheme by determining its measurement efficiency to be 0.5\%.

quant-ph↗

arXiv2023

State Expansion of a Levitated Nanoparticle in a Dark Harmonic Potential

Levitated nanoparticles in vacuum are prime candidates for generating macroscopic quantum superposition states of massive objects. Most protocols for preparing these states necessitate coherent expansion beyond the scale of the zero-point motion to produce sufficiently delocalized and pure phase-space distributions. Here, we spatially expand and subsequently recontract the thermal state of a levitated nanoparticle by modifying the stiffness of the trap holding the particle. We achieve state-expansion factors of 25 in standard deviation for a particle initially feedback-cooled to a center-of-mass thermal state of \SI{155}{\milli\kelvin}. Our method relies on a hybrid scheme combining an optical trap, for cooling and measuring the particle's motion, with a Paul trap for expanding its state. Consequently, state expansion occurs devoid of measurement backaction from photon recoil, making this approach suitable for coherent wavefunction expansion in future experiments.

quant-ph↗

arXiv2023

Hybrid Paul-optical trap with large optical access for levitated optomechanics

We present a hybrid trapping platform that allows us to levitate a charged nanoparticle in high vacuum using either optical fields, radio-frequency fields, or a combination thereof. Our hybrid approach combines an optical dipole trap with a linear Paul trap while maintaining a large numerical aperture (0.77 NA). We detail a controlled transfer procedure that allows us to use the Paul trap as a safety net to recover particles lost from the optical trap at high vacuum. The presented hybrid platform adds to the toolbox of levitodynamics and represents an important step towards fully controllable dark potentials, providing control in the absence of decoherence due to photon recoil.

quant-ph↗

arXiv2023

Spinning a levitated mechanical oscillator far into the deep-strong coupling regime

The field of levitodynamics has made substantial advancements in manipulating the translational and rotational degrees of freedom of levitated nanoparticles. Notably, rotational degrees of freedom can now be cooled to millikelvin temperatures and driven into GHz rotational speeds. However, in the case of cylindrically symmetric nanorotors, only the rotations around their short axes have been effectively manipulated, while the possibility to control rotation around the longer axis has remained a notable gap in the field. Here, we extend the rotational control toolbox by engineering an optically levitated nanodumbbell in vacuum into controlled spinning around its long axis with spinning rates exceeding 1 GHz. This fast spinning introduces deep-strong coupling between the nanodumbell's libration modes, such that the coupling rate $g$ exceeds the bare libration frequencies $Ω_0$ by two orders of magnitude with $g/Ω_0=724\pm 33$. Our control over the long-axis rotation opens the door to study the physics of deep-strong coupled mechanical oscillators and to observe macroscopic rotational quantum interference effects, thus laying a solid foundation for future applications in quantum technologies. Additionally, we find that our system offers great potential as a nanoscopic gyroscope with competitive sensitivity.

physics.optics↗

arXiv2023

Cavity-mediated long-range interactions in levitated optomechanics

The ability to engineer cavity-mediated interactions has emerged as a powerful tool for the generation of non-local correlations and the investigation of non-equilibrium phenomena in many-body systems. Levitated optomechanical systems have recently entered the multi-particle regime, with promise for using arrays of massive strongly coupled oscillators for exploring complex interacting systems and sensing. Here, by combining advances in multi-particle optical levitation and cavity-based quantum control, we demonstrate, for the first time, programmable cavity-mediated interactions between nanoparticles in vacuum. The interaction is mediated by photons scattered by spatially separated particles in a cavity, resulting in strong coupling ($G_\text{zz}/Ω_\text{z} = 0.238\pm0.005$) that does not decay with distance within the cavity mode volume. We investigate the scaling of the interaction strength with cavity detuning and inter-particle separation, and demonstrate the tunability of interactions between different mechanical modes. Our work paves the way towards exploring many-body effects in nanoparticle arrays with programmable cavity-mediated interactions, generating entanglement of motion, and using interacting particle arrays for optomechanical sensing.

quant-ph↗