arXiv subjects

Tobias Huber

Publications and source records attributed to Tobias Huber.

At least 73 records · Page 4Linked to original sources

arXiv2017

Hyper-entanglement of photons emitted by a quantum dot

Entanglement is a unique quantum mechanical attribute and a fundamental resource of quantum technologies. Entanglement can be achieved in various individual degrees of freedom, nonetheless some systems are able to create simultaneous entanglement in multiple degrees of freedom - hyper-entanglement. A hyper-entangled state of light represents a valuable tool capable of reducing the experimental requirements and resource overheads and it can improve the success rate of quantum information protocols. Here, we report on demonstration of polarization and time-bin hyper-entangled photons emitted from a single quantum dot. We achieved this result by applying resonant and coherent excitation on a quantum dot system with marginal fine structure splitting. Our results yield fidelities to the maximally entangled state of 0.81(6) and 0.87(4) in polarization and time-bin, respectively.

quant-ph↗

arXiv2016

Two-body non-leptonic heavy-to-heavy decays at NNLO in QCD factorization

We evaluate in the framework of QCD factorization the two-loop vertex corrections to the decays $\bar{B}_{(s)}\to D_{(s)}^{(\ast)+} \, L^-$ and $Λ_b \to Λ_c^+ \, L^-$, where $L$ is a light meson from the set $\{π,ρ,K^{(\ast)},a_1\}$. These decays are paradigms of the QCD factorization approach since only the colour-allowed tree amplitude contributes at leading power. Hence they are sensitive to the size of power corrections once their leading-power perturbative expansion is under control. Here we compute the two-loop ${\cal O}(α_s^2)$ correction to the leading-power hard scattering kernels, and give the results for the convoluted kernels almost completely analytically. Our newly computed contribution amounts to a positive shift of the magnitude of the tree amplitude by $\sim 2$\%. We then perform an extensive phenomenological analysis to NNLO in QCD factorization, using the most recent values for non-perturbative input parameters. Given the fact that the NNLO perturbative correction and updated values for form factors increase the theory prediction for branching ratios, while experimental central values have at the same time decreased, we reanalyze the role and potential size of power corrections by means of appropriately chosen ratios of decay channels.

hep-ph↗

arXiv2016

Time-bin Entanglement from Quantum Dots

The desire to have a source of single entangled photon pairs can be satisfied using single quantum dots as emitters. However, we are not bound to pursue only polarization entanglement, but can also exploit other degrees of freedom. In this chapter we focus on the time degree of freedom, to achieve so-called time-bin entanglement. This requires that we prepare the quantum dot coherently into the biexciton state and also build special interferometers for analysis. Finally this technique can be extended to achieve time-bin and polarization hyper-entanglement from a suitable quantum dot.

quant-ph↗

arXiv2016

Effects of photo-neutralization on the emission properties of quantum dots

In this paper we investigate the coherence properties of a quantum dot under two-photon resonant excitation in combination with an additional photo-neutralization laser. The photo-neutralization increases the efficiency of the excitation process and thus, the brightness of the source, by a factor of approximately 1.5 for biexciton-exciton pairs. This enhancement does not degrade the relevant coherences in the system; neither the single photon coherence time, nor the coherence of the excitation process.

quant-ph↗

arXiv2015

Optimal excitation conditions for indistinguishable photons from quantum dots

In this letter, we present a detailed, all optical study of the influence of different excitation schemes on the indistinguishability of single photons from a single InAs quantum dot. For this study, we measure the Hong-Ou-Mandel interference of consecutive photons from the spontaneous emission of an InAs quantum dot state under various excitation schemes and different excitation conditions and give a comparison.

quant-ph↗

arXiv2015

Flavour, Electroweak Symmetry Breaking and Dark Matter: state of the art and future prospects

With the discovery of the Higgs boson the Standard Model has become a complete and comprehensive theory, which has been verified with unparalleled precision and in principle might be valid at all scales. However, several reasons remain why we firmly believe that there should be physics beyond the Standard Model. Experiments such as the LHC, new $B$ factories, and earth- and space-based astro-particle experiments provide us with unique opportunities to discover a coherent framework for many of the long-standing puzzles of our field. Here we explore several significant interconnections between the physics of the Higgs boson, the physics of flavour, and the experimental clues we have about dark matter.

hep-ph↗

arXiv2015

Two-loop current-current operator contribution to the non-leptonic QCD penguin amplitude

The computation of direct CP asymmetries in charmless B decays at next-to-next-to-leading order (NNLO) in QCD is of interest to ascertain the short-distance contribution. Here we compute the two-loop penguin contractions of the current-current operators Q_{1,2} and provide a first estimate of NNLO CP asymmetries in penguin-dominated b -> s transitions.

hep-ph↗

arXiv2015

Inclusive B -> X_s l^+ l^-: Complete angular analysis and a thorough study of collinear photons

We investigate logarithmically enhanced electromagnetic corrections of all angular observables in inclusive B -> X_s l^+ l^-. We present analytical results, which are supplemented by a dedicated Monte Carlo study on the treatment of collinear photons in order to determine the size of the electromagnetic logarithms. We then give the Standard Model predictions of all observables, considering all available NNLO QCD, NLO QED and power corrections, and investigate their sensitivity to New Physics. Since the structure of the double differential decay rate is modified in the presence of QED corrections, we also propose new observables which vanish if only QCD corrections are taken into account. Moreover, we study the experimental sensitivity to these new observables at Belle II.

hep-ph↗

arXiv2015

Coherence and degree of time-bin entanglement from quantum dots

We report on the generation of time-bin entangled photon pairs from a semiconductor quantum dot via pulsed resonant biexciton generation. Based on theoretical modeling we optimized the duration of the excitation pulse to minimize the laser-induced dephasing and increase the biexciton-to-background single exciton occupation probability. This results in a high degree of entanglement with a concurrence of up to 0.78(6) and a 0.88(3) overlap with a maximally entangled state. Theoretical simulations also indicate a power dependent nature of the dephasing during the laser excitation that limits the coherence of the excitation process.

quant-ph↗

arXiv2015

Two-loop master integrals for non-leptonic heavy-to-heavy decays

We compute the two-loop master integrals for non-leptonic heavy-to-heavy decays analytically in a recently-proposed canonical basis. For this genuine two-loop, two-scale problem we first derive a basis for the master integrals that disentangles the kinematics from the space-time dimension in the differential equations, and subsequently solve the latter in terms of iterated integrals up to weight four. The solution constitutes another valuable example of the finding of a canonical basis for two-loop master integrals that have two different internal masses, and assumes a form that is ideally suited for a subsequent convolution with the light-cone distribution amplitude in the framework of QCD factorisation.

hep-ph↗

arXiv2015

The (Q_7,Q_{1,2}) contribution to B -> X_s gamma at O(alpha_s^2)

Interference between the photonic dipole operator Q_7 and the current-current operators Q_{1,2} gives one of the most important QCD corrections to the B -> X_s gamma decay rate. So far, the O(alpha_s^2) part of this correction has been known in the heavy charm quark limit only (m_c >> m_b/2). Here, we evaluate this part at m_c=0, and use both limits in an updated phenomenological study. Our prediction for the CP- and isospin-averaged branching ratio in the Standard Model reads B^SM_{s gamma} = (3.36 +_ 0.23) * 10^-4 for E_gamma > 1.6 GeV.

hep-ph↗

arXiv2014

Quantum non-Gaussian Depth of Single-Photon States

We introduce and experimentally explore the concept of quantum non-Gaussian depth of single-photon states with a positive Wigner function. The depth measures the robustness of a single-photon state against optical losses. The directly witnessed quantum non-Gaussianity withstands significant attenuation, exhibiting a depth of 18 dB, while the nonclassicality remains unchanged. Quantum non-Gaussian depth is an experimentally approachable quantity that is much more robust than the negativity of the Wigner function. Furthermore, we use it to reveal significant differences between otherwise strongly nonclassical single-photon sources.

quant-ph↗

arXiv2014

Non-leptonic B-decays at two-loops in QCD

I review the status of the calculation of two-loop QCD corrections to non-leptonic B-decays in the framework of QCD factorisation. In the case of heavy-to-light decays I will cover the leading penguin amplitudes a_4^u and a_4^c. For heavy-to-heavy transitions I will discuss the amplitude a_1(D^(*) pi). In both cases I will present some computational details, especially on how to obtain analytical results for the master integrals in a canonical basis, which in turn enables us to derive analytical expressions for almost all terms in the amplitudes.

hep-ph↗

arXiv2014

Master integrals for the two-loop penguin contribution in non-leptonic B-decays

We compute the master integrals that arise in the calculation of the leading penguin amplitudes in non-leptonic B-decays at two-loop order. The application of differential equations in a canonical basis enables us to give analytic results for all master integrals in terms of iterated integrals with rational weight functions. It is the first application of this method to the case of two different internal masses.

hep-ph↗

arXiv2014

Polarization entangled photons from quantum dots embedded in nanowires

We present a first measurement of photon polarization entanglement from the biexciton to ground state cascade of a single InAsP quantum dot embedded in an InP nanowire. We observe a fidelity of 0.76(2) to a reference maximally entangled state as well as a concurrence of 0.57(6).

quant-ph↗

arXiv2014

Efficiency vs. multi-photon contribution test for quantum dots

The development of linear quantum computing within integrated circuits demands high quality semiconductor single photon sources. In particular, for a reliable single photon source it is not sufficient to have a low multi-photon component, but also to possess high efficiency. We investigate the photon statistics of the emission from a single quantum dot with a method that is able to sensitively detect the trade-off between the efficiency and the multi-photon contribution. Our measurements show, that the light emitted from the quantum dot when it is resonantly excited possess a very low multi-photon content. Additionally, we demonstrated, for the first time, the non-Gaussian nature of the quantum state emitted from a single quantum dot.

quant-ph↗

arXiv2014

Time-bin entangled photons from a quantum dot

Long distance quantum communication is one of the prime goals in the field of quantum information science. With information encoded in the quantum state of photons, existing telecommunication fiber networks can be effectively used as a transport medium. To achieve this goal, a source of robust entangled single photon pairs is required. While time-bin entanglement offers the required robustness, currently used parametric down-conversion sources have limited performance due to multi-pair contributions. We report the realization of a source of single time-bin entangled photon pairs utilizing the biexciton-exciton cascade in a III/V self-assembled quantum dot. We analyzed the generated photon pairs by an inherently phase-stable interferometry technique, facilitating uninterrupted long integration times. We confirmed the entanglement by performing a quantum state tomography of the emitted photons, which yielded a fidelity of 0.69(3) and a concurrence of 0.41(6).

quant-ph↗

arXiv2013

The four-loop cusp anomalous dimension in N=4 super Yang-Mills and analytic integration techniques for Wilson line integrals

Correlation functions of Wilson lines are relevant for describing the infrared structure of scattering amplitudes. We develop a new method for evaluating a wide class of such Wilson line integrals, and apply it to the calculation of the velocity-dependent cusp anomalous dimension in maximally supersymmetric Yang-Mills theory. We compute the four-loop non-planar correction in a recently introduced scaling limit. Moreover, we derive the full planar four-loop result by means of an ansatz which is based on the structure of known analytic results. We determine the coefficients in this ansatz by making use of a relationship to massive scattering amplitudes. As a corollary, our analytical result confirms the four-loop value of the light-like cusp anomalous dimension. Finally, we use the available perturbative data, as well as insight from AdS/CFT, in order to extrapolate the leading order values at strong coupling. The latter agree within two per cent with the corresponding string theory result, over a wide range of parameters.

hep-th↗