Bulletin of the American Physical Society
54th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 68, Number 7
Monday–Friday, June 5–9, 2023; Spokane, Washington
Session E10: Open Quantum Systems |
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Chair: Zhifan Zhou, University of Maryland Room: 207 |
Tuesday, June 6, 2023 2:00PM - 2:12PM |
E10.00001: Quantum-to-Classical transition enabled by quadrature PT-symmetry Jianming Wen, Yanhua Zhai, Wencong Wang, Dongmei Liu, Xiaoshun Jiang, Saeid Vashahri Ghamsari Quantum Langevin noise makes experimental realization of genuine quantum-optical parity-time (PT) symmetry in a gain-loss-coupled open system elusive. Here, we challenge this puzzle by exploiting twin beams produced from a nonlinear parametric process, one undergoing phase-sensitive linear quantum amplification (PSA) and the other engaging balanced loss merely. Unlike all previous studies involving phase-insensitive amplification (PIA), our PSA-loss scheme allows one quadrature pair to experience PT symmetry, a unique quantum effect without any classical counterpart. Such symmetry showcases many radical noise behaviors beyond conventional quantum squeezing and inaccessible to any PIA-based platform. Importantly, it is the only non-Hermitian system hitherto that enables the emergence of non-Hermiticity-induced quantum-to-classical transition for the same quantum observable when crossing exceptional point. Utilizing this quadrature-PT structure, we have further studied its potential in quantum sensing by exploring the quantum Cramer-Rao bound or Fisher information. Besides, the proposed quadrature PT symmetry also sheds new light on protecting continuous-variable (CV) qubits from decoherence in lossy transmission, a long-standing conundrum for various CV-based quantum technologies. |
Tuesday, June 6, 2023 2:12PM - 2:24PM |
E10.00002: Quantum Back-action Limits in Dispersively Measured Bose-Einstein Condensates Emine Altuntas, Ian B Spielman Most quantum technologies simultaneously require quantum limited measurements and feedback control to establish and maintain quantum coherence and entanglement, with applications ranging from quantum state preparation to quantum error correction. Large-scale applications of these capabilities hinge on understanding system-reservoir dynamics of many-body quantum systems, whose Hilbert space grows exponentially with system size. Ultracold atoms are an ideal platform for understanding the system-reservoir dynamics of many-body systems. In this talk, I will present the characterization of measurement back-action in atomic Bose-Einstein condensates, weakly interacting with a far-from resonant, i.e., dispersively interacting, laser beam. We theoretically describe this process using a quantum trajectories approach where the environment measures the scattered light and I will present our measurement model based on an ideal photodetection mechanism. Next, I will discuss our experimental quantification of the resulting wavefunction change with two observations: the contrast of a Ramsey interferometer [1] and the deposited energy [2]. These results are necessary precursors for achieving true quantum back-action limited measurements of quantum gases and open the door to quantum feedback control of ultracold atoms. [1] E. Altuntas and I. B. Spielman, arXiv preprint arXiv:2209.04400 (2022). [2] E. Altuntas and I. B. Spielman, arXiv preprint arXiv:2212.03431 (2022). |
Tuesday, June 6, 2023 2:24PM - 2:36PM |
E10.00003: A phonon laser in the quantum regime Tanja Behrle, Thanh Long Nguyen, Florentin Reiter, David Baur, Brennan de Neeve, Martin Stadler, Matteo Marinelli, Francesco Lancellotti, Susanne F Yelin, Jonathan Home We demonstrate a trapped-ion system with two competing dissipation channels, implemented independently on two ion species co-trapped in a Paul trap. By controlling coherent spin-oscillator couplings and optical pumping rates we explore the phase diagram of this system, which exhibits a regime analogous to that of a (phonon) laser but operates close to the quantum ground state with an average phonon number of below ten. We demonstrate phase locking of the oscillator to an additional resonant drive, and also observe the phase diffusion of the resulting state under dissipation by reconstructing the quantum state from a measurement of the characteristic function. |
Tuesday, June 6, 2023 2:36PM - 2:48PM |
E10.00004: Dissipative Spin Squeezing via Strong Symmetries in Collective Multilevel Systems Jeremy T Young, Edwin Chaparro, Asier Piñeiro Orioli, James K Thompson, Ana Maria Rey In many-body quantum systems, the environment tends to destroy quantum entanglement via dissipation. However, it is also possible to instead harness the effect of the environment as a resource to prepare useful quantum entanglement. In this talk, I will discuss how driven-dissipative cavities coupled to a collective ensemble of multilevel atoms can dynamically generate metrologically useful spin-squeezed states. In contrast to other dissipative approaches, we do not rely on complex engineered dissipation or input states, nor do we require tuning the system to a critical point. Instead, we utilize a strong symmetry, a special type of symmetry which can occur in open quantum systems and emerges naturally in collective multilevel systems. I will demonstrate how this symmetry allows for the generation of spin-squeezed states via emergent one-axis twisting dynamics and discuss how our approach provides dramatic advantages over comparable dissipative and coherent approaches for implementation in state-of-the-art optical clocks. |
Tuesday, June 6, 2023 2:48PM - 3:00PM |
E10.00005: Dissipative Generation of Spin Squeezing with Multilevel Atoms: Beyond the Bad Cavity Limit Edwin Chaparro, Jeremy T Young, Diego Barberena, Asier Piñeiro Orioli, James K Thomson, Ana M Rey We study a protocol for the dissipative generation of spin squeezing with multilevel atoms in an optical cavity via photon-mediated interactions. We demonstrate that for a broad regime of cavity parameters that go beyond the bad cavity limit, it is possible to generate robust spin squeezing in the full multilevel system and transfer it to the ground state manifold by turning off the drive with no additional pulses. We show that there is minimal deterioration of the squeezing due to the system's strong symmetry, a particular type of symmetry that can emerge in open quantum systems. We verify these capabilities via dissipative phase space methods which use Monte Carlo sampling and stochastic noise to properly capture the build up of quantum correlations in dissipative systems. These methods allow us to explore the parameter regimes where analytical approaches break down under conditions that are relevant to current cavity-QED experiments and are useful for the next generation of atomic clocks. |
Tuesday, June 6, 2023 3:00PM - 3:12PM |
E10.00006: Describing Local Decoherence of Spin Ensembles using a Fokker-Planck Equation in a Bosonic Mode Andrew K Forbes, Philip D Blocher, Ivan H Deutsch Many protocols seek to prepare nonclassical states of spin ensembles through an atom-light interface. When uniformly coupled, and evolving under unitary dynamics, this is simply described by the collective spin in the symmetric subspace. However, optical pumping, in which spins flip their orientation and scatter a photon into the environment, breaks this symmetry as the scattered photon will carry information about the location of the spin into the environment. This results in local decoherence (LD), which is typically inefficient to describe for large ensembles of atoms. In this work we develop a formalism that represents LD for a large number of spins using a Wigner function on a bosonic mode by making use of the Holstein-Primakoff approximation. The dynamics of the bosonic mode can be described using a Fokker-Planck equation at zero temperature. We use this formalism to study the combined effect of Hamiltonian evolution, local and collective decoherence, and measurement backaction for preparing nonclassical spin states for quantum metrology. |
Tuesday, June 6, 2023 3:12PM - 3:24PM |
E10.00007: Observation of exceptional points and skin effect in a 2D non-Hermitian topological band Entong ZHAO, Chengdong HE, Ka Kwan Pak, Yujun Liu, Peng Ren, Gyu-Boong Jo The open quantum system, which can be effectively described by a non-Hermitian Hamiltonian, often shows a spectral singularity known as exceptional points. Recently, the concept of non-Hermitian has also been generalized to the lattice system in which the exceptional points are created in the band structure in momentum space and many intriguing phenomena have been theoretically explored. In this talk, we report the realization of a 2D non-Hermitian topological band in an optical Raman lattice with tunable dissipation for ultracold fermions. Within this platform, we observe the emergence and shift of the exceptional points in our 2D topological band when the spin-dependent dissipation increases. With momentum-dependent Rabi spectroscopy, the band gap information can be reconstructed from the time evolution of spin texture. The reconstructed spectral topology in the complex energy plane further indicates the existence of skin effect in our optical Raman lattice system. It is expected that this platform would allow us to further expand the possibilities to explore the unique phenomena in non-Hermitian lattice systems. |
Tuesday, June 6, 2023 3:24PM - 3:36PM |
E10.00008: Non-Hermitian Absorption Spectroscopy Kai Li, Yong Xu While non-Hermitian Hamiltonians have been experimentally realized in cold atom systems, it remains an outstanding open question of how to experimentally measure their complex energy spectra in momentum space for a realistic system with boundaries. The existence of non-Hermitian skin effects may make the question even more difficult to address given the fact that energy spectra for a system with open boundaries are dramatically different from those in momentum space; the fact may even lead to the notion that momentum-space band structures are not experimentally accessible for a system with open boundaries. Here, we generalize the widely used radio-frequency spectroscopy to measure both real and imaginary parts of complex energy spectra of a non-Hermitian quantum system for either bosonic or fermionic atoms. By weakly coupling the energy levels of a non-Hermitian system to auxiliary energy levels, we theoretically derive a formula showing that the decay of atoms on the auxiliary energy levels reflects the real and imaginary parts of energy spectra in momentum space. We further prove that measurement outcomes are independent of boundary conditions in the thermodynamic limit, providing strong evidence that the energy spectrum in momentum space is experimentally measurable. We finally apply our non-Hermitian absorption spectroscopy protocol to the Hatano-Nelson model and non-Hermitian Weyl semimetals to demonstrate its feasibility. |
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