Thermal noise and optomechanical features in the emission of a membrane-coupled compound cavity laser diode

We demonstrate the use of a compound optical cavity as linear displacement detector, by measuring the thermal motion of a silicon nitride suspended membrane acting as the external mirror of a near-infrared Littrow laser diode. Fluctuations in the laser optical power induced by the membrane vibrations are collected by a photodiode integrated within the laser, and then measured with a spectrum analyzer. The dynamics of the membrane driven by a piezoelectric actuator is investigated as a function of air pressure and actuator displacement in a homodyne configuration. The high Q-factor ($\sim 3.4\cdot 10^4$ at $8.3 \cdot 10^{-3}$ mbar) of the fundamental mechanical mode at $\sim 73$ kHz guarantees a detection sensitivity high enough for direct measurement of thermal motion at room temperature ($\sim 87$ pm RMS). The compound cavity system here introduced can be employed as a table-top, cost-effective linear displacement detector for cavity optomechanics. Furthermore, thanks to the strong optical nonlinearities of the laser compound cavity, these systems open new perspectives in the study of non-Markovian quantum properties at the mesoscale

Stretching graphene using polymeric micro-muscles

The control of strain in two-dimensional materials opens exciting perspectives for the engineering of their electronic properties. While this expectation has been validated by artificial-lattice studies, it remains elusive in the case of atomic lattices. Remarkable results were obtained on nanobubbles and nano-wrinkles, or using scanning probes; microscale strain devices were implemented exploiting deformable substrates or external loads. These devices lack, however, the flexibility required to fully control and investigate arbitrary strain profiles. Here, we demonstrate a novel approach making it possible to induce strain in graphene using polymeric micrometric artificial muscles (MAMs) that contract in a controllable and reversible way under an electronic stimulus. Our method exploits the mechanical response of poly-methyl-methacrylate (PMMA) to electron-beam irradiation. Inhomogeneous anisotropic strain and out-of-plane deformation are demonstrated and studied by Raman, scanning-electron and atomic-force microscopy. These can all be easily combined with the present device architecture. The flexibility of the present method opens new opportunities for the investigation of strain and nanomechanics in two-dimensional materials

Anisotropic straining of graphene using micropatterned SiN membranes

We use micro-Raman spectroscopy to study strain profiles in graphene monolayers suspended over SiN membranes micropatterned with holes of non-circular geometry. We show that a uniform differential pressure load $\Delta P$ over elliptical regions of free-standing graphene yields measurable deviations from hydrostatic strain conventionally observed in radially-symmetric microbubbles. The top hydrostatic strain $\bar{\varepsilon}$ we observe is estimated to be $\approx0.7\%$ for $\Delta P = 1\,{\rm bar}$ in graphene clamped to elliptical SiN holes with axis $40$ and $20\,{\rm \mu m}$. In the same configuration, we report a $G_\pm$ splitting of $10\,{\rm cm^{-1}}$ which is in good agreement with the calculated anisotropy $\Delta\varepsilon \approx 0.6\%$ for our device geometry. Our results are consistent with the most recent reports on the Gr\"uneisen parameters. Perspectives for the achievement of arbitrary strain configurations by designing suitable SiN holes and boundary clamping conditions are discussed.Comment: 8 pages, 6 figure (including SI

NNLO Logarithmic Expansions and High Precision Determinations of the QCD background at the LHC: The case of the Z resonance

New methods of solutions of the DGLAP equation and their implementation through NNLO in QCD are briefly reviewed. We organize the perturbative expansion that describes in $x$-space the evolved parton distributions in terms of scale invariant functions, which are determined recursively, and logarithms of the ratio of the running couplings at the initial and final evolution scales. Resummed solutions are constructed within the same approach and involve logarithms of more complex functions, which are given in the non-singlet case. Differences in the evolution schemes are shown to be numerically sizeable and intrinsic to perturbation theory. We illustrate these points in the case of Drell-Yan lepton pair production near the Z resonance, analysis that can be extended to searches of extra $Z^{\prime}$. We show that the reduction of the NNLO cross section compared to the NLO prediction may be attributed to the NNLO evolution.Comment: 5 pages, 2 figures. Talk given at QCD@work 2007, Martina Franca, Italy, 16-20 June 2007. To be published in the American Institute of Physics (AIP) conference proceeding

Liquid Biopsy in Rare Cancers: Lessons from Hemangiopericytoma

Hemangiopericytoma (HPT) is a rare mesenchymal tumor of fibroblastic type and for its rarity is poorly studied. The most common sites of metastatic disease in patients with intracranial HPT are the bone, liver, and lung, suggestive for an hematogenous dissemination; for this reason, we investigated, for the first time, the presence of circulating tumor cells (CTCs) in hemangiopericytoma patient by CellSearch® and SceenCell® devices. Peripheral blood samples were drawn and processed by CellSearch, an EpCAM-dependent device, and ScreenCell®, a device size based. We found nontypical CTCs by CellSearch system and the immunofluorescence analysis performed on CTCs isolate by ScreenCell demonstrated the presence of single CTCs and CTC clusters. The molecular characterization of single CTCs and CTC clusters, using antibodies directed against EpCAM, CD34, cytokeratins (8, 18, and 19), and CD45, showed a great heterogeneity in CTC clusters. We believe that the present study may open a new scenario in the rare tumors: the introduction of the liquid biopsy and the molecular characterization of circulating tumor cells could lead to personalized targeted treatments and also for rare tumors

Naso-Ethmoidal Phosphaturic Mesenchymal Tumor: A Rare Tumor Site for an Uncommon Paraneoplastic Syndrome

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A Nanocryotron Ripple Counter Integrated with a Superconducting Nanowire Single-Photon Detector for Megapixel Arrays

Decreasing the number of cables that bring heat into the cryocooler is a critical issue for all cryoelectronic devices. Especially, arrays of superconducting nanowire single-photon detectors (SNSPDs) could require more than $10^6$ readout lines. Performing signal processing operations at low temperatures could be a solution. Nanocryotrons, superconducting nanowire three-terminal devices, are good candidates for integrating sensing and electronics on the same technological platform as SNSPDs in photon-counting applications. In this work, we demonstrated that it is possible to read out, process, encode, and store the output of SNSPDs using exclusively superconducting nanowires. In particular, we present the design and development of a nanocryotron ripple counter that detects input voltage spikes and converts the number of pulses to an $N$-digit value. The counting base can be tuned from 2 to higher values, enabling higher maximum counts without enlarging the circuit. As a proof-of-principle, we first experimentally demonstrated the building block of the counter, an integer-$N$ frequency divider with $N$ ranging from 2 to 5. Then, we demonstrated photon-counting operations at 405\,nm and 1550\,nm by coupling an SNSPD with a 2-digit nanocryotron counter partially integrated on-chip. The 2-digit counter operated in either base 2 or base 3 with a bit error rate lower than $2 \times 10^{-4}$ and a maximum count rate of $45 \times 10^6\,$s$^{-1}$. We simulated circuit architectures for integrated readout of the counter state, and we evaluated the capabilities of reading out an SNSPD megapixel array that would collect up to $10^{12}$ counts per second. The results of this work, combined with our recent publications on a nanocryotron shift register and logic gates, pave the way for the development of nanocryotron processors, from which multiple superconducting platforms may benefit

A Nanocryotron Memory and Logic Family

The development of superconducting electronics based on nanocryotrons has been limited so far to few-device circuits, in part due to the lack of standard and robust logic cells. Here, we introduce and experimentally demonstrate designs for a set of nanocryotron-based building blocks that can be configured and combined to implement memory and logic functions. The devices were fabricated by patterning a single superconducting layer of niobium nitride and measured in liquid helium on a wide range of operating points. The tests show $10^{-4}$ bit error rates with above $20\,\%$ margins up to $50\,$MHz and the possibility of operating under the effect of a perpendicular $36\,$mT magnetic field, with $30\,\%$ margins at $10\,$MHz. Additionally, we designed and measured an equivalent delay flip-flop made of two memory cells to show the possibility of combining multiple building blocks to make larger circuits. These blocks may constitute a solid foundation for the development of nanocryotron logic circuits and finite-state machines with potential applications in the integrated processing and control of superconducting nanowire single-photon detectors.Comment: Submitted for publication in the Applied Physics Letters special issue "Advances in Superconducting Logic", 8 pages, 5 figure