arXiv subjects

Adarsh S. Prasad

Publications and source records attributed to Adarsh S. Prasad.

6 recordsLinked to original sources

arXiv2025

Properties of quantum emitters in different hBN sample types particularly suited for nanophotonic integration

Single photon emitters in two-dimensional (2D) hexagonal boron nitride (hBN) are promising solid-state quantum emitters for photonic applications and quantum networks. Despite their favorable properties, much is still unknown about their characteristics and their atomic origin. We focus on two different kinds of hBN samples that particularly lend themselves for integration with nanophotonic devices, multilayer nanoflakes produced by liquid phase exfoliation (LPE) and a layer-engineered sample from hBN grown by chemical vapour deposition (CVD). We investigate their inherent defects and fit their emission properties to computationally simulated optical properties of likely carbon-related defects. Thereby we compare and elucidate the properties in different sample types particularly suited for photonic quantum networks and narrow down the origin of emitters found in these samples. Our work is thus an important step towards harnessing the full potential of single photon emitters in hBN.

quant-ph↗

arXiv2021

Unraveling two-photon entanglement via the squeezing spectrum of light traveling through nanofiber-coupled atoms

We observe that a weak guided light field transmitted through an ensemble of atoms coupled to an optical nanofiber exhibits quadrature squeezing. From the measured squeezing spectrum we gain direct access to the phase and amplitude of the energy-time entangled part of the two-photon wavefunction which arises from the strongly correlated transport of photons through the ensemble. For small atomic ensembles we observe a spectrum close to the lineshape of the atomic transition, while sidebands are observed for sufficiently large ensembles, in agreement with our theoretical predictions. Furthermore, we vary the detuning of the probe light with respect to the atomic resonance and infer the phase of the entangled two-photon wavefunction. From the amplitude and the phase of the spectrum, we reconstruct the real- and imaginary part of the time-domain wavefunction. Our characterization of the entangled two-photon component constitutes a diagnostic tool for quantum optics devices.

quant-ph↗

arXiv2021

Thermal tuning of a fiber-integrated Fabry-Pérot cavity

Here, we present the thermal tuning capability of an alignment-free fiber-integrated Fabry-Pérot cavity.The two mirrors are made of fiber Bragg gratings that can be individually temperature stabilized and tuned. We show the temperature tuning of the resonance wavelength of the cavity without any degradation of the finesse and the tuning of the individual stop bands of the fiber Bragg gratings. This not only permits for the cavity's finesse to be optimized post-fabrication but also makes this cavity applicable as a narrowband filter with a FWHM spectral width of 0.07 (0.02) pm and a suppression of more than -15 dB that can be wavelength tuned. Further, in the field of quantum optics, where strong light-matter interactions are desirable, quantum emitters can be coupled to such a cavity and the cavity effect can be reversibly omitted and re-established. This is particularly useful when working with solid-state quantum emitters where such a reference measurement is often not possible once an emitter has been permanently deposited inside a cavity.

physics.ins-det↗

arXiv2019

Correlating photons using the collective nonlinear response of atoms weakly coupled to an optical mode

Photons in a nonlinear medium can repel or attract each other, resulting in a strongly correlated quantum many-body system. Typically, such strongly correlated states of light arise from the extreme nonlinearity granted by quantum emitters that are strongly coupled to a photonic mode. However, in these approaches, unavoidable dissipation, like photon loss, blurs nonlinear quantum effects. Here, we generate strongly correlated photon states using only weak coupling and taking advantage of dissipation. We launch light through an ensemble of non-interacting waveguide-coupled atoms, which induce correlations between simultaneously arriving photons through collectively enhanced nonlinear interactions. These correlated photons then experience less dissipation than the uncorrelated ones. Depending on the number of atoms, we experimentally observe strong photon bunching or anti-bunching of the transmitted light. This realization of a collectively enhanced nonlinearity may turn out transformational for quantum information science and opens new avenues for generating nonclassical light, covering frequencies from the microwave to the X-ray regime.

quant-ph↗

arXiv2015

Complete temporal characterization of a single photon

Precise information about the temporal mode of optical states is crucial for optimizing their interaction efficiency between themselves and/or with matter in various quantum communication devices. Here we propose and experimentally demonstrate a method of determining both the real and imaginary components of a single photon's temporal density matrix by measuring the autocorrelation function of the photocurrent from a balanced homodyne detector at multiple local oscillator frequencies. We test our method on single photons heralded from biphotons generated via four-wave mixing in an atomic vapor and obtain excellent agreement with theoretical predictions for several settings.

quant-ph↗

arXiv2013

Distillation of the two-mode squeezed state

We experimentally demonstrate entanglement distillation of the two mode squeezed state. Applying the annihilation operator to both modes, we increase the fraction of the two-photon component in the state, resulting in the increase of both squeezing and entanglement by about 50%.

quant-ph↗