By viewing a character in a text as a particle that can occupy one of a finite collection of states (the letter “A”, the letter “T”, the number “7”, …) one can interpret samples of natural language as observations of a one-dimensional system of interacting particles.  I’ll review some of the engineering developments that led to the state-of-the-art large language models in use today and argue that the mathematical structures at work behind the scenes are consistent with this physical view and sheds a little light, not just on how LLMs work, but how human language itself might work.
 

As the ability to control electromagnetic fields through engineered photonic structures grows, so does our need for field mapping techniques with subwavelength resolution. Here, we use a scanning diamond nanocrystal to investigate the interplay between the emission of room-temperature nitrogen-vacancy (NV) centers and a proximal topological waveguide. The NV photoluminescence serves as a local, spectrally broad light source to characterize the waveguide response, both in terms of its wavelength bandwidth as well as the correspondence between light injection site and directionality of wave propagation. Further, we find that near-field coupling between the emitters and the waveguide chiral modes influences the ellipticity of the NV photoluminescence, hence allowing us to reveal nanostructured light fields with a spatial resolution defined by the nanoparticle size. Our results pave the route to exploiting color centers as photonic sensors, an approach that also promises opportunities in the development of on-chip devices integrating single-photon emitters and quantum optics.

A Zoom Seminar at the Department of Chemistry at Lehman College and the Department of Physics at Queens College

You are invited to a Zoom meeting.
When: Oct 30, 2024 12:00 PM Eastern Time (US and Canada)

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https://us06web.zoom.us/meeting/register/tZEpdOqrrjIqE9NIRUSU3N3IA04w99SvB6bs

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When electrons are injected through chiral molecules, the resulting current may become spin polarized. This effect, known as the chirality-induced spin-selectivity (CISS) effect,  has been suggested to emerge due to the interplay between spin–orbit interactions and the chirality within the molecule. However, such explanations require unrealistically large values for the molecular spin–orbit interaction without any physical justification. Put simply, to date, the physical origin of  the CISS effect is unknown.

I will present the “spinterface mechanism” for the CISS effect, based on the interplay between spin–orbit interactions in the electrode, the chirality of the molecule (which induces a solenoid field), and spin-transfer torque at the molecule–electrode interface. I will show the remarkable agreement between the spinterface theory and various experimental results, and will describe a set of “smoking gun” experiments for differentiating these mechanisms from other theoretical explanations. Finally, we will describe a spinterface mechanism for the CISS effect in photo-excited electrons scattered off a layer of chiral molecules.

[1] S. Alwan & Y. Dubi, Spinterface Origin for the Chirality-Induced Spin-Selectivity Effect, J. Am. Chem. Soc. 143, 35, 14235–14241 (2021)
[2] Y. Dubi, Spinterface chirality-induced spin selectivity effect in bio-molecules, Chem. Sci., 13, 10878-1088 (2022).
[3] C. Yang, Y. Li, S. Zhou, Y. Guo, C. Jia, Z. Liu, K. N. Houk, Y. Dubi & X Guo, Real-time monitoring of reaction stereochemistry through single-molecule observations of chirality-induced spin selectivity, Nature Chemistry 15, 972–979 (2023)
[4] Seif Alwan, Subhajit Sarkar, Amos Sharoni, Yonatan Dubi, Temperature-dependence of the CISS effect from measurements in Chiral molecular intercalation super-lattices, J. Chem. Phys. 159, 014106 (2023).
[5] S. Alwan, A. Sharoni &  Y.  Dubi, Role of Electrode Polarization in the Electron Transport Chirality-Induced Spin-Selectivity Effect, J. Phys. Chem. C 128, 15, 6438–6445 (2024).

It is realized that by interfacing BCS superconductors and semiconductors with strong spin--orbit coupling it is possible to create a system that can host exotic states of matter. Hence epitaxial superconductors and semiconductors have emerged as an attractive materials system with atomically sharp interfaces and broad flexibility in device fabrications incorporating Josephson junctions.  We place our Al-InAs Josephson junction into circuit quantum electrodynamics to directly probe the Andreev bound states. We probe the microwave photons from a superconducting resonator that are coupled to the junction. These measurements reveal a coupling interaction between the resonator and the Andreev bound states, enabling the mapping of isolated individual Andreev bound states characterized by near-unity transparency and a substantial induced superconducting gap. Exploration of the gate parameter space illustrates the evolution of Andreev bound states with gate voltage, revealing the mapping of multiple Andreev bound states.
 

During the noisy intermediate-scale quantum (NISQ) era, quantum computational approaches refined to overcome the challenge of limited quantum resources are highly valuable. However, the accuracy of the molecular properties predicted by most of the quantum computations nowadays is still far off (not within chemical accuracy) compared to their corresponding experimental data. Here, we propose a promising qubit-efficient quantum computational approach to calculate the harmonic vibrational frequencies of a large set of neutral closed-shell diatomic molecules with results in great agreement with their experimental data [1,2]. We attribute the great performance of the proposed method to three factors: (i) a better description of the Hamiltonian by introducing the Daubechies wavelets molecular orbitals, (ii) incorporating the electron correlation effect into the molecular orbitals via the exchange functional, (iii) a suitable selection of active space based on an energy criterion of a first-order pair energy in the theory of independent electron pair approximation. Remarkably, our proposed approach significantly reduces the number of qubits required for the 43 diatomic molecules from 20 to 60 with the use of the traditional cc-pVDZ basis set and the frozen core approximation to only 2 to 12, but with similar accuracy for the obtained results [2]. This verifies that the harmonic vibrational frequencies of molecules could be calculated accurately by quantum computation in the NISQ era [2,3]. Our benchmark investigation provides a critical assessment on the power of quantum computation of molecular properties and insights on further improvements.

References:

• 1]. C.-L. Hong, T. Tsai, J.-P. Chou et al., P.-J. Chen, P.-K. Tsai, Y.-C. Chen, E.-J. Kuo, D. Srolovitz, A. Hu, Y.-C. Cheng, and H.-S. Goan*, “Accurate and efficient quantum computations of molecular properties using Daubechies wavelet molecular orbitals: a benchmark study against experimental data”, PRX Quantum 3, 020360 (2022).
• 2]. S.-K. Chou, J.-P. Chou, A. Hu, Y.-C. Cheng*, and H.-S. Goan*, “Accurate Harmonic Vibrational Frequencies for Diatomic Molecules via Quantum Computing”, Physical Review Research 5, 043216 (2023)
• 3]. C.-T. Chu, S.-K. Chou, and H.-S. Goan*, “Demonstration of quantum computation of molecular properties in agreement with experimental data on NISQ devices,” in preparation (2024).