10 research outputs found
Robust kHz-linewidth distributed Bragg reflector laser with optoelectronic feedback
We demonstrate a combination of optical and electronic feedback that
significantly narrows the linewidth of distributed Bragg reflector lasers
(DBRs). We use optical feedback from a long external fiber path to reduce the
high-frequency noise of the laser. An electro-optic modulator placed inside the
optical feedback path allows us to apply electronic feedback to the laser
frequency with very large bandwidth, enabling robust and stable locking to a
reference cavity that suppresses low-frequency components of laser noise. The
combination of optical and electronic feedback allows us to significantly lower
the frequency noise power spectral density of the laser across all frequencies
and narrow its linewidth from a free-running value of 1.1 MHz to a stabilized
value of 1.9 kHz, limited by the detection system resolution. This approach
enables the construction of robust lasers with sub-kHz linewidth based on DBRs
across a broad range of wavelengths.Comment: 5 pages, 3 figure
Near-Unitary Spin Squeezing in Yb
Spin squeezing can improve atomic precision measurements beyond the standard
quantum limit (SQL), and unitary spin squeezing is essential for improving
atomic clocks. We report substantial and nearly unitary spin squeezing in
Yb, an optical lattice clock atom. The collective nuclear spin of atoms is squeezed by cavity feedback, using light detuned from the
system's resonances to attain unitarity. The observed precision gain over the
SQL is limited by state readout to 6.5(4) dB, while the generated states offer
a gain of 12.9(6) dB, limited by the curvature of the Bloch sphere. Using a
squeezed state within 30% of unitarity, we demonstrate an interferometer that
improves the averaging time over the SQL by a factor of 3.7(2). In the future,
the squeezing can be simply transferred onto the optical clock transition of
Yb.Comment: 5 pages, 4 figure
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Highly efficient transfection of human induced pluripotent stem cells using magnetic nanoparticles.
PurposeThe delivery of transgenes into human induced pluripotent stem cell (hiPSC)-derived cardiomyocytes (hiPSC-CMs) represents an important tool in cardiac regeneration with potential for clinical applications. Gene transfection is more difficult, however, for hiPSCs and hiPSC-CMs than for somatic cells. Despite improvements in transfection and transduction, the efficiency, cytotoxicity, safety, and cost of these methods remain unsatisfactory. The objective of this study is to examine gene transfection in hiPSCs and hiPSC-CMs using magnetic nanoparticles (NPs).MethodsMagnetic NPs are unique transfection reagents that form complexes with nucleic acids by ionic interaction. The particles, loaded with nucleic acids, can be guided by a magnetic field to allow their concentration onto the surface of the cell membrane. Subsequent uptake of the loaded particles by the cells allows for high efficiency transfection of the cells with nucleic acids. We developed a new method using magnetic NPs to transfect hiPSCs and hiPSC-CMs. HiPSCs and hiPSC-CMs were cultured and analyzed using confocal microscopy, flow cytometry, and patch clamp recordings to quantify the transfection efficiency and cellular function.ResultsWe compared the transfection efficiency of hiPSCs with that of human embryonic kidney (HEK 293) cells. We observed that the average efficiency in hiPSCs was 43%±2% compared to 62%±4% in HEK 293 cells. Further analysis of the transfected hiPSCs showed that the differentiation of hiPSCs to hiPSC-CMs was not altered by NPs. Finally, robust transfection of hiPSC-CMs with an efficiency of 18%±2% was obtained.ConclusionThe difficult-to-transfect hiPSCs and hiPSC-CMs were efficiently transfected using magnetic NPs. Our study offers a novel approach for transfection of hiPSCs and hiPSC-CMs without the need for viral vector generation
High-Velocity Saturation in Graphene Encapsulated by Hexagonal Boron Nitride
We
measure drift velocity in monolayer graphene encapsulated by
hexagonal boron nitride (hBN), probing its dependence on carrier density
and temperature. Due to the high mobility (>5 × 10<sup>4</sup> cm<sup>2</sup>/V/s) of our samples, the drift velocity begins to
saturate at low electric fields (∼0.1 V/μm) at room temperature.
Comparing results to a canonical drift velocity model, we extract
room-temperature electron saturation velocities ranging from 6 ×
10<sup>7</sup> cm/s at a low carrier density of 8 × 10<sup>11</sup> cm<sup>–2</sup> to 2.7 × 10<sup>7</sup> cm/s at a higher
density of 4.4 × 10<sup>12</sup> cm<sup>–2</sup>. Such
drift velocities are much higher than those in silicon (∼10<sup>7</sup> cm/s) and in graphene on SiO<sub>2</sub>, likely due to reduced
carrier scattering with surface optical phonons whose energy in hBN
(>100 meV) is higher than that in other substrates
Highly efficient transfection of human induced pluripotent stem cells using magnetic nanoparticles
The delivery of transgenes into human induced pluripotent stem cell (hiPSC)-derived cardiomyocytes (hi PSC-C Ms) represents an important tool in cardiac regeneration with potential for clinical applications. Gene transfection is more difficult, however, for hiPSCs and hi PSC-CMs than for somatic cells. Despite improvements in transfection and transduction, the efficiency, cytotoxicity, safety, and cost of these methods remain unsatisfactory. The objective of this study is to examine gene transfection in hiPSCs and hiPSC-CMs using magnetic nanoparticles (NPs). Methods: Magnetic NPs are unique transfection reagents that form complexes with nucleic acids by ionic interaction. The particles, loaded with nucleic acids, can be guided by a magnetic field to allow their concentration onto the surface of the cell membrane. Subsequent uptake of the loaded particles by the cells allows for high efficiency transfection of the cells with nucleic acids. We developed a new method using magnetic NPs to transfect hiPSCs and hiPSC-CMs. HiPSCs and hiPSC-CMs were cultured and analyzed using confbcal microscopy, flow cytometry, and patch clamp recordings to quantify the transfection efficiency and cellular function. Results: We compared the transfection efficiency of hiPSCs with that of human embryonic kidney (HEK 293) cells. We observed that the average efficiency in hi PSCs was 43%+/- 2% compared to 62%+/- 4% in HEK 293 cells. Further analysis of the transfected hiPSCs showed that the differentiation of hiPSCs to hi PSC-CMs was not altered by NPs. Finally, robust transfection of hi PSC-CMs with an efficiency of I8%+/- 2% was obtained. Conclusion: The difficult-to-transfect hiPSCs and hiPSC-CMs were efficiently transfected using magnetic NPs. Our study offers a novel approach for transfection of hiPSCs and hiPSCCMs without the need for viral vector generation
Hexagonal boron nitride as a low-loss dielectric for superconducting quantum circuits and qubits
Dielectrics with low loss at microwave frequencies are imperative for
high-coherence solid-state quantum computing platforms. We study the dielectric
loss of hexagonal boron nitride (hBN) thin films in the microwave regime by
measuring the quality factor of parallel-plate capacitors (PPCs) made of
NbSe-hBN-NbSe heterostructures integrated into superconducting
circuits. The extracted microwave loss tangent of hBN is bounded to be at most
in the mid-10 range in the low temperature, single-photon regime. We
integrate hBN PPCs with aluminum Josephson junctions to realize transmon qubits
with coherence times reaching 25 s, consistent with the hBN loss tangent
inferred from resonator measurements. The hBN PPC reduces the qubit feature
size by approximately two-orders of magnitude compared to conventional
all-aluminum coplanar transmons. Our results establish hBN as a promising
dielectric for building high-coherence quantum circuits with substantially
reduced footprint and, with a high energy participation that helps to reduce
unwanted qubit cross-talk