Joint Seminar on Quantum Information and Technologies
2012/2013 | 2013/2014 | 2014/2015 | 2015/2016 | 2016/2017 | 2017/2018 | 2018/2019 | 2019/2020 | 2020/2021 | 2021/2022 | 2022/2023 | 2023/2024 | 2024/2025 | YouTube channel
until 2023/2024 Quantum Information Seminar | YouTube channel
2023-09-25 (Monday)
room 1.40, Pasteura 5 at 14:15 
Michael Raymer (University of Oregon)Quantum Telescopy: Interferometric Imaging using Shared Quantum Entanglement [Distinguished Lectures on Complex Systems and Quantum Physics series]
Quantum entanglement-based imaging promises significantlyincreased resolution by extending the spatial separation of opticalcollection apertures used in very-long-baseline interferometry forastronomy and geodesy. We report a table-top entanglement-basedinterferometric imaging technique that utilizes two entangled fieldmodes serving as a phase reference between two apertures. The spatialdistribution of a simulated thermal light source is determined byinterfering light collected at each aperture with one of the entangledfields and performing joint measurements. This experiment demonstratesthe ability of entanglement to implement interferometric imaging. SeeBrown, Matthew R., Markus Allgaier, Valérian Thiel, John Monnier,Michael G. Raymer, and Brian J. Smith. "Interferometric imaging usingshared quantum entanglement." arXiv preprint arXiv:2212.07395
2023-07-19 (Wednesday)
room B0.14, Pasteura 5 at 11:15
Ray-Kuang Lee (National Tsing Hua University, Taiwan)Experimental Realization of Optical Cat States with Single-Photon-Added Squeezed States
In this talk, I will first illustrate the implementation of our machine-learning (ML) enhanced quantum state tomography (QST) for continuous variables, through the experimentally measured data generated from squeezed vacuum states [1], as an example of quantum machine learning [2, 3]. Then, this ML-enhanced QST is also applied to the heralding single photon source, which has the second order correlation function, g2 < 0.04 [4]. Instead of ‘‘Schrodinger kitten’’ state generated by subtracting one photon from a squeezed vacuum beam, we report the first experimental realization of optical cat states by adding one photon to a squeezed vacuum state [5]. A variety of unique applications in linear optical quantum computing and quantum metrology will also be addressed [6].
[1] Hsien-Yi Hsieh, et al., "Extract the Degradation Information in Squeezed States with Machine Learning," Phys. Rev. Lett. 128, 073604 (2022).
[2] Hsien-Yi Hsieh, et al., "Direct parameter estimations from machine-learning enhanced quantum state tomography," Special Issue "Quantum Optimization & Machine Learning"; Symmetry 14, 874 (2022).
[3] Alexey Melnikov, Mohammad Kordzanganeh, Alexander Alodjants, and RKL," Quantum Machine Learning: from physics to software engineering," Adv. in Phys. X (Review Article) 8, 2165452 (2023).
[4] Yi-Ru, et al., "Machine-learning enhanced quantum state tomography for the heralding single photon source," (in preparation, 2023).
[5] Yi-Ru, et al., "Experimental Realization of Optical Cat States with Single-Photon-Added Squeezed States," arXiv: 2306.13011 (2023).
[6] Yuhang Zhao, et al., "Frequency-dependent squeezed vacuum source for broadband quantum noise reduction in advanced gravitational-wave detectors," Phys. Rev. Lett. 124, 171101 (2020); Editors' Suggestion; Featured in Physics.
[1] Hsien-Yi Hsieh, et al., "Extract the Degradation Information in Squeezed States with Machine Learning," Phys. Rev. Lett. 128, 073604 (2022).
[2] Hsien-Yi Hsieh, et al., "Direct parameter estimations from machine-learning enhanced quantum state tomography," Special Issue "Quantum Optimization & Machine Learning"; Symmetry 14, 874 (2022).
[3] Alexey Melnikov, Mohammad Kordzanganeh, Alexander Alodjants, and RKL," Quantum Machine Learning: from physics to software engineering," Adv. in Phys. X (Review Article) 8, 2165452 (2023).
[4] Yi-Ru, et al., "Machine-learning enhanced quantum state tomography for the heralding single photon source," (in preparation, 2023).
[5] Yi-Ru, et al., "Experimental Realization of Optical Cat States with Single-Photon-Added Squeezed States," arXiv: 2306.13011 (2023).
[6] Yuhang Zhao, et al., "Frequency-dependent squeezed vacuum source for broadband quantum noise reduction in advanced gravitational-wave detectors," Phys. Rev. Lett. 124, 171101 (2020); Editors' Suggestion; Featured in Physics.
2023-07-11 (Tuesday)
room 1.02, Pasteura 5 at 11:15
Gabriel Santamaria Botello (University of Colorado Boulder)Photonics for low-noise microwave-to-THz detection: Techniques and applications
Recently, there has been an increased interest in platforms that coherently convert photons from the microwave to the optical domain. This has been mainly motivated by the advent of quantum information technologies because room-temperature photonic links could transfer quantum states between cryogenic superconducting microwave circuits over long distances. While several approaches are under investigation to this end, there is a second potential application of efficient photonic upconverters that is often overlooked: Low-noise detection of weak signals at microwave, millimeter-wave, and THz frequencies by using photodetectors with an upconverter as an intermediary. Even at room temperature, this technique could one day surpass the noise performance of cryogenic low-noise amplifiers (LNAs) and mixers at microwave/THz frequencies, enabling applications in areas such as radio astronomy, space instrumentation, earth observation, etc.
In this talk we will briefly introduce electro-optic modulators based on high-Q lithium niobate whispering-gallery mode resonators serving as upconverters in both lab setups, and photonic integrated circuit platforms. Then, we will discuss coherent Rydberg-atom electrometers exploiting electromagnetically induced transparency (EIT) and Autler-Townes (AT) splitting effects to optically detect microwave signals. By acknowledging that most practical microwave engineering applications would require coupling of these atomic receivers to a microwave port rather than free-space, we engineered high-Q field-enhancing microwave cavities. However, a trade-off is found between field enhancement and thermal noise introduced by the cavity due to its physical temperature. This leads to an optimal coupling strength or impedance mismatch that minimizes total noise, analogous to the optimal noise reflection coefficient of the first-stage transistor in an LNA. We will overview the theory behind these findings as well as the preliminary experimental results we have obtained along with a few unexpected challenges. Finally, perspectives will be given on other possible RF and microwave engineering applications currently getting the attention of funding agencies.
In this talk we will briefly introduce electro-optic modulators based on high-Q lithium niobate whispering-gallery mode resonators serving as upconverters in both lab setups, and photonic integrated circuit platforms. Then, we will discuss coherent Rydberg-atom electrometers exploiting electromagnetically induced transparency (EIT) and Autler-Townes (AT) splitting effects to optically detect microwave signals. By acknowledging that most practical microwave engineering applications would require coupling of these atomic receivers to a microwave port rather than free-space, we engineered high-Q field-enhancing microwave cavities. However, a trade-off is found between field enhancement and thermal noise introduced by the cavity due to its physical temperature. This leads to an optimal coupling strength or impedance mismatch that minimizes total noise, analogous to the optimal noise reflection coefficient of the first-stage transistor in an LNA. We will overview the theory behind these findings as well as the preliminary experimental results we have obtained along with a few unexpected challenges. Finally, perspectives will be given on other possible RF and microwave engineering applications currently getting the attention of funding agencies.
2023-07-06 (Thursday)
room 2.23, Pasteura 5 at 11:15
Nir Davidson (Dept. of Physics of Complex Systems, Weizmann Institute of Science, Rehovot, Israel)Simulating XY spins with coupled lasers
We investigate phase locking of large arrays of coupled lasers in a modified degenerate cavity. We show that the minimal loss lasing solution is mapped onto the ground state of an XY spin Hamiltonian when all the laser intensities are uniform. We study the probability to obtain this ground state for various coupling schemes, system parameters and topological constrains. We demonstrate the effects of quenched disorder, Crowd Synchrony, Artificial Gauge Fields and non-Hermitian Physics. Finally, we use our system to solve related problems such as phase retrieval, imaging through scattering medium, many-body mode interactions, and more.
2023-06-29 (Thursday)
room 1.03, Pasteura 5 at 11:15
Peter Groszkowski (University of Chicago)Adventures in Quantum Information Science: non-Markovian Noise Modeling, Enhancing Ramsey-based Quantum Metrology with Spin Amplification, and Modeling of Superconducting Circuits with scqubits
In this talk I will give an overview of a few recent projects related to various topics in quantum information.Driven quantum systems subject to non-Markovian noise are typically difficult to model even if the noise is classical. In the first part of my talk, I will present a systematic method based on a generalized cumulant expansion for deriving a time-local master equation for such systems [1]. I will outline some key features of such a master equation, and show that it can lead to dynamics that is much more accurate than a more standard method that is often used for modeling the effects of correlated noise.In the second part, I will explore how dissipative dynamics of ensembles of two-level systems can be used to enhance Ramsey-based quantum metrology approaches that are limited by detection noise [2]. In particular I will explore how a collective spin decay, an effect that is usually seen as a nuisance because it limits spin-squeezing protocols, can allow a system with extremely imperfect detection to approach the standard-quantum-limit (SQL) within a factor of about (approximately) 2.Finally, I will briefly discuss scqubits: an open-source Python package for simulating and analyzing superconducting circuits [3]. I will outline its core functionality, features, as well as limitations.
[1] PG, A Seif, J Koch, AA Clerk, Quantum 7, 972 (2023)[2] M Koppenhöfer, PG, H-K Lau, AA Clerk, PRX Quantum 3 (3), 030330 (2022)[3] PG, J Koch, Quantum 5, 583 (2021)
[1] PG, A Seif, J Koch, AA Clerk, Quantum 7, 972 (2023)[2] M Koppenhöfer, PG, H-K Lau, AA Clerk, PRX Quantum 3 (3), 030330 (2022)[3] PG, J Koch, Quantum 5, 583 (2021)
2023-06-15 (Thursday)
room 1.02, Pasteura 5 at 11:15
Filip Rozpędek (University of Chicago)All-photonic multiplexed quantum repeaters based on concatenated bosonic and discrete-variable quantum codes
Long distance quantum communication will require the use of quantum repeaters to overcome the exponential attenuation of signal with distance. One class of such repeaters utilizes quantum errorcorrection to overcome losses in the communication channel. Here we propose a novel strategy of using the bosonic Gottesman-Kitaev-Preskill (GKP) code in a two-way repeater architecture withmultiplexing. The crucial feature of the GKP code that we make use of is the fact that GKP qubits easily admit deterministic two-qubit gates, hence allowing for multiplexing without the need forgenerating large cluster states as required in previous all-photonic architectures based on discretevariable codes. Moreover, alleviating the need for such clique-clusters entails that we are no longerlimited to extraction of at most one end-to-end entangled pair from a single protocol run. In fact,thanks to the availability of the analog information generated during the measurements of the GKPqubits, we can design better entanglement swapping procedures in which we connect links based ontheir estimated quality. This enables us to use all the multiplexed links so that large number of linksfrom a single protocol run can contribute to the generation of the end-to-end entanglement. We findthat our architecture allows for high-rate end-to-end entanglement generation and is resilient toimperfections arising from finite squeezing in the GKP state preparation and homodyne detectioninefficiency. In particular we show that long-distance quantum communication over more than 1000km is possible even with less than 13 dB of GKP squeezing. We also quantify the number of GKPqubits needed for the implementation of our scheme and find that for good hardware parametersour scheme requires around 103−104 GKP qubits per repeater per protocol run.This work is available on arxiv at arXiv:2303.14923
2023-06-05 (Monday)
room 1.02, Pasteura 5 at 10:00
Dayou Yang (Ulm University)New opportunities for sensing via continuous measurement
The continuous monitoring of driven-dissipative quantum optical systems provides key strategies for the implementation of quantum metrology, with prominent examples ranging from the gravitational wave detectors to the emergent driven-dissipative many-body sensors. Fundamental theoretical questions about the ultimate performance of such a class of sensors remain open—for example, can they achieve quantum-enhanced precision scaling without squeezed input; how to perform the optimal measurement to approach their ultimate precision? In this talk, I will present our recent efforts to answer these questions. In the first part I will introduce dissipative criticality as a resource for nonclassical precision scaling for continuously monitored sensors, by establishing universal scaling laws of the quantum Fisher information in terms of the critical exponents of generic dissipative critical points. In the second part I will present a general continuous measurement strategy to retrieve the full quantum Fisher information of the nonclassical, temporally correlated fields emitted by generic open quantum sensors, thereby to achieve their fundamental precision limit.
2023-06-01 (Thursday)
room 1.02, Pasteura 5 at 11:15
Marcin Kotowski (CFT PAN)Extremal jumps of circuit complexity of unitary evolutions generated by random Hamiltonians
We investigate circuit complexity of unitaries generated by time evolution of randomly chosen strongly interacting Hamiltonians in finite dimensional Hilbert spaces. Specifically, we focus on two ensembles of random generators -- the so called Gaussian Unitary Ensemble (GUE) and the ensemble of diagonal Gaussian matrices conjugated by Haar random unitary transformations. In both scenarios we prove that the complexity of exp(−itH) exhibits a surprising behaviour -- with high probability it reaches the maximal allowed value on the same time scale as needed to escape the neighborhood of the identity consisting of unitaries with trivial (zero) complexity. We furthermore observe similar behaviour for quantum states originating from time evolutions generated by above ensembles and for diagonal unitaries generated from the ensemble of diagonal Gaussian Hamiltonians. To establish these results we rely heavily on structural properties of the above ensembles (such as unitary invariance) and concentration of measure techniques. This gives us a much finer control over the time evolution of complexity compared to techniques previously employed in this context: high-degree moments and frame potentials.
2023-05-25 (Thursday)
room 1.02, Pasteura 5 at 11:15
Michał Oszmaniec (CFT PAN)Pretty good simulation of all quantum measurements by projective measurements in finite-dimensional quantum systems
In quantum theory general measurements are described by so-called Positive Operator-Valued Measures (POVMs). In this work we show that in d-dimensional quantum systems an application of depolarizing noise with constant (independent of d) visibility parameter makes any POVM simulable by a randomized implementation of projective measurements that do not require any auxiliary systems to be realized.This result significantly limits the asymptotic advantage that POVMs can offer over projective measurements in various information-processing tasks, including state discrimination, shadow tomography or quantum metrology. We also apply our findings to questions originating from quantum foundations. First, we asymptotically improve the range of parameters for which Werner and isotropic states have local models for generalized measurements (by factors of d and log(d) respectively). Second, we give asymptotically tight (in terms of dimension) bounds on critical visibility for which all POVMs are jointly measurable. On the technical side we use recent advances in POVM simulation, the solution to the celebrated Kadison-Singer problem, and a method of approximate implementation of a class of "nearly rank one" POVMs by a convex combination of projective measurements, which we call dimension-deficient Naimark extension theorem.The talk will be based on upcoming joint work with Michał Kotowski (MIM UW)
2023-05-18 (Thursday)