Variational simulation of Schwinger's Hamiltonian with polarization qubits

O. V. Borzenkova, G. I. Struchalin, A. S. Kardashin, V. V. Krasnikov, N. N. Skryabin, S. S. Straupe, S. P. Kulik, and J. D. Biamonte

Applied Physics Letters, 119, 144002 (2021)

The numerical emulation of quantum physics and quantum chemistry often involves an intractable number of degrees of freedom and admits no known approximation in the general form. In practice, representing quantum-mechanical states using available numerical methods becomes exponentially more challenging with increasing system size. Recently, quantum algorithms implemented as variational models have been proposed to accelerate such simulations. Here, we study the effect of noise on the quantum phase transition in the Schwinger model within a variational framework. The experiments are built using a free space optical scheme to realize a pair of polarization qubits and enable any two-qubit state to be experimentally prepared up to machine tolerance. We specifically exploit the possibility to engineer noise and decoherence for polarization qubits to explore the limits of variational algorithms for noisy intermediate-scale quantum architectures in identifying and quantifying quantum phase transitions with noisy qubits. We find that despite the presence of noise, one can detect the phase transition of the Schwinger Hamiltonian even for a two-qubit system using variational quantum algorithms.

Single-walled carbon nanotube membranes as non-reflective substrates for nanophotonic applications

Denis M Zhigunov, Daniil A Shilkin, Natalia G Kokareva, Vladimir O Bessonov, Sergey A Dyakov, Dmitry A Chermoshentsev, Aram A Mkrtchyan, Yury G Gladush, Andrey A Fedyanin and Albert G Nasibulin

IOP Science "Nanotechnology", 32, 095206 (2021)

We demonstrate that single-walled carbon nanotube (SWCNT) membranes can be successfully utilized as nanometer-thick substrates for enhanced visualization and facilitated study of individual nanoparticles. As model objects, we transfer optically resonant 200 nm silicon nanoparticles onto pristine and ethanol-densified SWCNT membranes by the femtosecond laser printing method. We image nanoparticles by scanning electron and bright-field optical microscopy, and characterize by linear and Raman scattering spectroscopy. The use of a pristine SWCNT membrane allows to achieve an order-of-magnitude enhancement of the optical contrast of the nanoparticle bright field image over the results shown in the case of the glass substrate use. The observed optical contrast enhancement is in agreement with the spectrophotometric measurements showing an extremely low specular reflectance of the pristine membrane (≤0.1%). Owing to the high transparency, negligibly small reflectance and thickness, SWCNT membranes offer a variety of perspective applications in nanophotonics, bioimaging and synchrotron radiation studies.

Experimental Estimation of Quantum State Properties from Classical Shadows

G.I. Struchalin, Ya. A. Zagorovskii, E.V. Kovlakov, S.S. Straupe, and S.P. Kulik

PRX Quantum, 2, 010307 (2021)

Full quantum tomography of high-dimensional quantum systems is experimentally infeasible due to the exponential scaling of the number of required measurements on the number of qubits in the system. However, several ideas have been proposed recently for predicting the limited number of features for these states, or estimating the expectation values of operators, without the need for full state reconstruction. These ideas go under the general name of shadow tomography. Here, we provide an experimental demonstration of property estimation based on classical shadows proposed in Huang et al. [Nat. Phys. 16, 1050 (2020)] and study its performance in a quantum-optical experiment with high-dimensional spatial states of photons. We show by means of experimental data how this procedure outperforms conventional state reconstruction in fidelity estimation from a limited number of measurements.

Linear optical circuits characterization by means of thermal field correlation measurement

K. G. Katamadze, G. V. Avosopiants, A. V. Romanova, Yu. I. Bogdanov and S. P. Kulik

Laser Physics Letters, 19, 075201 (2021)

We present a novel technique for linear optical circuits characterization, based on thermal field correlation measurements. Unlike the other known methods for multichannel interferometers measurements, proposed technique is robust to the input and output phase fluctuations and does not require any single-photon sources and detectors. This method has been tested in a numerical experiment and has proven to be effective even in the presence of noise.
Effect of pyrolysis on microstructures made of various photoresists by two-photon polymerization: comparative study

M. I. Sharipova, T. G. Baluyan, K. A. Abrashitova, G. E. Kulagin, A. K. Petrov, A. S. Chizhov, T. B. Shatalova, D. Chubich, D. A. Kolymagin, A. G. Vitukhnovsky, V. O. Bessonov, and A. A. Fedyanin

Optical Materials Express, 11, 371-384 (2021)

Two-photon laser polymerization (TPP) is a state-of-the-art technology that allows for the submicron-resolution printing of freeform 3D objects to be harnessed in various applications, including physics, biology, medicine, and materials science. The TPP is based on using photosensitive polymeric materials that impose restrictions on the minimum feature size and limit the functionality of printed structures within the capabilities of polymers. One of the promising yet insufficiently studied methods for overcoming these limitations is pyrolysis–high-temperature annealing of polymer objects in an inert atmosphere. It may allow both to decrease the size of the objects and modify their chemical composition. Here, we compare the effect of pyrolysis on solid objects being tens of micrometers in size printed by TPP from three commercially available photoresists: IP-Dip, OrmoComp, and SZ2080. For the annealing temperatures of 450°C and 690°C in an argon atmosphere, we assessed the changes in size, chemical composition, and adhesion to the silicon wafer substrate. Our data may be promising for developing pyrolysis as a standard post-processing method for structures created via TPP technology.