On-chip spin-orbit locking of quantum emitters in 2D materials for chiral emission

Light carries both spin angular momentum (SAM) and orbital angular momentum (OAM), which can be used as potential degrees of freedom for quantum information processing. Quantum emitters are ideal candidates towards on-chip control and manipulation of the full SAM–OAM state space. Here, we show coupling of a spin-polarized quantum emitter in a monolayer$WSe2$with the whispering gallery mode of a$Si3N4$ring resonator. The cavity mode carries a transverse SAM of$σ<#comment/>=±<#comment/>1$in the evanescent regions, with the sign depending on the orbital power flow direction of the light. By tailoring the cavity–emitter interaction, we couple the intrinsic spin state of the quantum emitter to the SAM and propagation direction of the cavity mode, which leads to spin–orbit locking and subsequent chiral single-photon emission. Furthermore, by engineering how light is scattered from the WGM, we create a high-order Bessel beam which opens up the possibility to generate optical vortex carrying OAM states.

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Publication Date:
NSF-PAR ID:
10369918
Journal Name:
Optica
Volume:
9
Issue:
8
Page Range or eLocation-ID:
Article No. 953
ISSN:
2334-2536
Publisher:
Optical Society of America
1. We experimentally demonstrate the utilization of adaptive optics (AO) to mitigate intra-group power coupling among linearly polarized (LP) modes in a graded-index few-mode fiber (GI FMF). Generally, in this fiber, the coupling between degenerate modes inside a modal group tends to be stronger than between modes belonging to different groups. In our approach, the coupling inside the$LP11$group can be represented by a combination of orbital-angular-momentum (OAM) modes, such that reducing power coupling in OAM set tends to indicate the capability to reduce the coupling inside the$LP11$group. We employ two output OAM modes$l=+1$and$l=−<#comment/>1$as resultant linear combinations of degenerate$LP11a$and$LP11b$modes inside the$LP11$group of a$∼<#comment/>0.6-km$GI FMF. The power coupling is mitigated by shaping the amplitude and phase of the distorted OAM modes. Each OAM mode carries an independent 20-, 40-, or 100-Gbit/s quadrature-phase-shift-keying data stream. We measure the transmission matrix (TM) in the OAM basis within$LP11$group, which is a subset of the full LP TMmore »
2. We experimentally demonstrate simultaneous turbulence mitigation and channel demultiplexing in a 200 Gbit/s orbital-angular-momentum (OAM) multiplexed link by adaptive wavefront shaping and diffusing (WSD) the light beams. Different realizations of two emulated turbulence strengths (the Fried parameter$r0=0.4,1.0mm$) are mitigated. The experimental results show the following. (1) Crosstalk between OAM$l=+1$and$l=−<#comment/>1$modes can be reduced by$><#comment/>10.0$and$><#comment/>5.8dB$, respectively, under the weaker turbulence ($r0=1.0mm$); crosstalk is further improved by$><#comment/>17.7$and$><#comment/>19.4dB$, respectively, under most realizations in the stronger turbulence ($r0=0.4mm$). (2) The optical signal-to-noise ratio penalties for the bit error rate performance are measured to be$∼<#comment/>0.7$and$∼<#comment/>1.6dB$under weaker turbulence, while measured to be$∼<#comment/>3.2$and$∼<#comment/>1.8dB$under stronger turbulence for OAM$l=+1$and$l=−<#comment/>1$mode, respectively.
3. We study the relationship between the input phase delays and the output mode orders when using a pixel-array structure fed by multiple single-mode waveguides for tunable orbital-angular-momentum (OAM) beam generation. As an emitter of a free-space OAM beam, the designed structure introduces a transformation function that shapes and coherently combines multiple (e.g., four) equal-amplitude inputs, with the$k$th input carrying a phase delay of$(k−<#comment/>1)Δ<#comment/>φ<#comment/>$. The simulation results show that (1) the generated OAM order ℓ is dependent on the relative phase delay$Δ<#comment/>φ<#comment/>$; (2) the transformation function can be tailored by engineering the structure to support different tunable ranges (e.g., $l={−<#comment/>1},{−<#comment/>1,+1},{−<#comment/>1,0,+1}$, or${−<#comment/>2,−<#comment/>1,+1,+2}$); and (3) multiple independent coaxial OAM beams can be generated by simultaneously feeding the structure with multiple independent beams, such that each beam has its own$Δ<#comment/>φ<#comment/>$value for the four inputs. Moreover, there is a trade-off between the tunable range and the mode purity, bandwidth, and crosstalk, such that the increase of the tunable range leads to (a) decreased mode purity (from 91% to 75% formore »), (b) decreased 3 dB bandwidth of emission efficiency (from 285 nm for$l={−<#comment/>1}$to 122 nm for$l={−<#comment/>2,−<#comment/>1,+1,+2}$), and (c) increased crosstalk within the C-band (from$−<#comment/>23.7$to$−<#comment/>13.2dB$when the tunable range increases from 2 to 4).
4. Electro-optic quantum coherent interfaces map the amplitude and phase of a quantum signal directly to the phase or intensity of a probe beam. At terahertz frequencies, a fundamental challenge is not only to sense such weak signals (due to a weak coupling with a probe in the near-infrared) but also to resolve them in the time domain. Cavity confinement of both light fields can increase the interaction and achieve strong coupling. Using this approach, current realizations are limited to low microwave frequencies. Alternatively, in bulk crystals, electro-optic sampling was shown to reach quantum-level sensitivity of terahertz waves. Yet, the coupling strength was extremely weak. Here, we propose an on-chip architecture that concomitantly provides subcycle temporal resolution and an extreme sensitivity to sense terahertz intracavity fields below 20 V/m. We use guided femtosecond pulses in the near-infrared and a confinement of the terahertz wave to a volume of$VTHz∼<#comment/>10−<#comment/>9(λ<#comment/>THz/2)3$in combination with ultraperformant organic molecules ($r33=170pm/V$) and accomplish a record-high single-photon electro-optic coupling rate of, 10,000 times higher than in recent reports of sensing vacuum field fluctuations in bulk media. Via homodyne detection implemented directly on chip, the interaction results into an intensity modulation of the femtosecond pulses. The single-photon cooperativity is$C0=1.6×<#comment/>10−<#comment/>8$, and the multiphoton cooperativity is$C=0.002$at room temperature. We show$><#comment/>70dB$dynamic range in intensity at 500 ms integration under irradiation with a weak coherent terahertz field. Similar devices could be employed in future measurements of quantum states in the terahertz at the standard quantum limit, or for entanglement of subsystems on subcycle temporal scales, such as terahertz and near-infrared quantum bits.
5. In this Letter, the electron-blocking-layer (EBL)-free AlGaN ultraviolet (UV) light-emitting diodes (LEDs) using a strip-in-a-barrier structure have been proposed. The quantum barrier (QB) structures are systematically engineered by integrating a 1 nm intrinsic$AlxGa(1−<#comment/>x)N$strip into the middle of QBs. The resulted structures exhibit significantly reduced electron leakage and improved hole injection into the active region, thus generating higher carrier radiative recombination. Our study shows that the proposed structure improves radiative recombination by$∼<#comment/>220%<#comment/>$, reduces electron leakage by$∼<#comment/>11$times, and enhances optical power by$∼<#comment/>225%<#comment/>$at 60 mA current injection compared to a conventional AlGaN EBL LED structure. Moreover, the EBL-free strip-in-a-barrier UV LED records the maximum internal quantum efficiency (IQE) of$∼<#comment/>61.5%<#comment/>$which is$∼<#comment/>72%<#comment/>$higher, and IQE droop is$∼<#comment/>12.4%<#comment/>$, which is$∼<#comment/>333%<#comment/>$less compared to the conventional AlGaN EBL LED structure at$∼<#comment/>284.5nm$wavelength. Hence, the proposed EBL-free AlGaN LED is the potential solution to enhance the optical power and produce highly efficient UV emitters.