Theory of Cold Atoms @ Seoul National University

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About Our Group

Quantum many-body physics investigates the complex and highly entangled behavior of interacting (elementary or composite) particles at ultralow temperatures. Our group explores the intricate and unexpected manifestations of the resulting emergent phenomena when many quantum degrees of freedom cooperate, which go fundamentally beyond those expected from the simple single-particle picture familiar from textbook scenarios.

Selected Publications

"Photonic" Cat States from Strongly Interacting Matter Waves
Uwe R. Fischer and Myung-Kyun Kang
Phys. Rev. Lett. 115, 260404 (2015).
Consistent perturbative treatment of the subohmic spin-boson model yielding arbitrarily small $T_2/T_1$ decoherence time ratios
Kyung-Joo Noh and Uwe R. Fischer
Phys. Rev. B 90, 220302 (Rapid Communication) (2014).
Revealing Single-Trap Condensate Fragmentation by Measuring Density-Density Correlations after Time of Flight
Myung-Kyun Kang and Uwe R. Fischer
Phys. Rev. Lett. 113, 140404 (2014).
Ultrafast quantum random access memory utilizing single Rydberg atoms in a Bose-Einstein condensate
Kelly R. Patton and Uwe R. Fischer
Phys. Rev. Lett. 111, 240504 (2013).
Fragmented many-body ground states for scalar bosons in a single trap
Philipp Bader and Uwe R. Fischer
Phys. Rev. Lett. 103, 060402 (2009).
Vortex quantum creation and winding number scaling in a quenched spinor Bose gas
Michael Uhlmann, Ralf Schützhold, and Uwe R. Fischer
Phys. Rev. Lett. 99, 120407 (2007).
Sweeping from the superfluid to the Mott phase in the Bose-Hubbard model
Ralf Schützhold, Michael Uhlmann, Yan Xu, and Uwe R. Fischer
Phys. Rev. Lett. 97, 200601 (2006).
Stability of quasi-two-dimensional Bose-Einstein condensates with dominant dipole-dipole interactions
Uwe R. Fischer
Phys. Rev. A 73, 031602 (Rapid Communication) (2006).
Quantum simulation of cosmic inflation in two-component Bose-Einstein condensates
Uwe R. Fischer and Ralf Schützhold
Phys. Rev. A 70, 063615 (2004).
"Cosmological" quasiparticle production in harmonically trapped superfluid gases
Petr O. Fedichev and Uwe R. Fischer
Phys. Rev. A 69, 033602 (2004).
Gibbons-Hawking Effect in the Sonic de Sitter Space-Time of an Expanding Bose-Einstein-Condensed Gas
Petr O. Fedichev and Uwe R. Fischer
Phys. Rev. Lett. 91, 240407 (2003).
Vortex states of rapidly rotating dilute Bose-Einstein condensates
Uwe R. Fischer and Gordon Baym
Phys. Rev. Lett. 90, 140402 (2003).
Existence of Long-Range Order for Trapped Interacting Bosons
Uwe R. Fischer
Phys. Rev. Lett. 89, 280402 (2002).

Members

Professor, Principal Investigator

Postdocs

Oleksandr V. Marchukov
Self-Consistent Many-Body Physics
56-519

Graduate Students

최석영 (Seok-yeong Chä)
Analogue Quantum Cosmology
56-520
윤태웅 (Tae-Woong Youn)
Hybrid Quantum Gates
56-517
신성호 (Seongho Shin)
Topological Defects in Ultracold Quantum Gases
56-517
NRF Global PhD Fellowship Holder
박상신 (Sangshin Park)
Analogue Gravity
56-520
정환철 (Hwan Chul Jung)
Quantum Memories
56-517
배승리 (Seunglee Bae)
Many-Body Effects in Quantum Information Processing
56-517
박재균 (Jae-gyun Park)
Quantum Metrology
56-520

Alumni

Postdocs

Graduate Students

강명균 (Myung-Kyun Kang)
Measurement Theory of Quantum Many-Body States
BK Thesis Excellence Award 2016

Undergraduate Students

노경주 (Kyung-Joo Noh)
Theory of Open Quantum Systems, Quantum Decoherence, and Quantum Thermalization
Now at Yale University

Research Interests

Hybrid Quantum Systems

This is the study of a long-lived and rapidly accessible quantum memory unit, for which the operational Hilbert space is spanned by states involving the two macroscopically occupied hyperfine levels of a miscible binary atomic Bose-Einstein condensate and the Rydberg state of a single atom. Our group have shown that an arbitrary qubit state, initially prepared using a flux qubit, can be rapidly transferred to and from the trapped atomic ensemble in approximately 10 ns and with a large fidelity of 97%, via an effective two-photon process using an external laser for the transition to the Rydberg level. The achievable ultrafast transfer of quantum information enables a large number of storage and retrieval cycles from the highly controllable quantum optics setup of a dilute ultracold gas, even within the typically very short flux qubit lifetimes of the order of microseconds.
[Related Publications]
Kelly R. Patton and Uwe R. Fischer, Ultrafast quantum random access memory utilizing single Rydberg atoms in a Bose-Einstein condensate, Phys. Rev. Lett. 111, 024504 (2013).
Kelly R. Patton and Uwe R. Fischer, Transfer and storage of qubits in the presence of decoherence, EPL 102, 20001 (2013).
Kelly R. Patton and Uwe R. Fischer, Hybrid of superconducting quantum interference device and atomic Bose-Einstein condensate: An architecture for quantum information processing, Phys. Rev. A 87, 052303 (2013).

Fragmented Condensates of Interacting Bosons as a Many-body Phenomenon

We investigate whether the many-body ground states of bosons in a generalized two-mode model with localized inhomogeneous single-particle orbitals and anisotropic long-range interactions (e.g., dipole-dipole interactions) are coherent or fragmented. It is demonstrated that fragmentation can take place in a single trap for positive values of the interaction couplings, implying that the system is potentially stable. Furthermore, the degree of fragmentation is shown to be insensitive to small perturbations on the single-particle level.
[Related Publications]
Philipp Bader and Uwe R. Fischer, Fragmented many-body ground states for scalar bosons in a single trap, Phys. Rev. Lett. 103, 060402 (2009).
Uwe R. Fischer and Bo Xiong, Robustness of fragmented condensate many-body states for continuous distribution amplitudes in Fock space, Phys. Rev. A 88, 053602 (2013).
Myung-Kyun Kang and Uwe R. Fischer, Revealing Single-Trap Condensate Fragmentation by Measuring Density-Density Correlations after Time of Flight, Phys. Rev. Lett. 113, 140404 (2014).

Atoms in Optical Lattices as Quantum Simulators for New Phases of Matter

We consider the rapid quench of a one-dimensional strongly correlated supersolid to a localized density wave (checkerboard) phase, and calculate the first-order coherence signal following the quench. It is shown that unique coherence oscillations between the even and odd sublattice sites of the checkerboard are created by the quench, which are absent when the initial state is described by a Gutzwiller product state. This is a striking manifestation of the versatility of the far-from-equilbrium and nonperturbative collapse and revival phenomenon as a microscope for quantum correlations in complex many-body states. For the present example, this opens up the possibility to discriminate experimentally between mean-field and many-body origins of supersolidity.
[Related Publications]
Uwe R. Fischer and Bo Xiong, Identifying strongly correlated supersolid states on the optical lattice by quench-induced $\pi$-states, EPL 99, 66003 (2012).
Bo Xiong and Uwe R. Fischer, Interaction-induced coherence among polar bosons stored in triple-well potentials, Phys. Rev. A 88, 063608 (2013).
Uwe R. Fischer and Bo Xiong, Many-site coherence revivals in the extended Bose-Hubbard model and the Gutzwiller approximation, Phys. Rev. A 84, 063635 (2011).

Analogue Gravity and Quantum Field Theory of Bogoliubov Excitations

A variety of cosmologically motivated effective quasiparticle space-times can be produced in harmonically trapped superfluid Bose and Fermi gases. We have studied the analog of cosmological particle production in these effective space-times, induced by trapping potentials and coupling constants possessing an arbitrary time dependence. The WKB probabilities for phonon creation from the superfluid vacuum have been calculated, and an experimental procedure to detect quasiparticle production by measuring density-density correlation functions was proposed.
[Related Publications]
Petr O. Fedichev and Uwe R. Fischer, "Cosmological" quasiparticle production in harmonically trapped superfluid gases, Phys. Rev. A 69, 033602 (2004).
Uwe R. Fischer and Ralf Schützhold, Quantum simulation of cosmic inflation in two-component Bose-Einstein condensates, Phys. Rev. A 70, 063615 (2004).
Petr O. Fedichev and Uwe R. Fischer, Gibbons-Hawking Effect in the Sonic de Sitter Space-Time of an Expanding Bose-Einstein-Condensed Gas, Phys. Rev. Lett. 91, 240407 (2003).

Publications

2017

Phase-fluctuating condensates are fragmented: An experimental benchmark for self-consistent quantum many-body calculations
Oleksandr V. Marchukov and Uwe R. Fischer
arXiv:1701.06821v1 [cond-mat.quant-gas] (2017).

2016

Probing the Scale Invariance of the Inflationary Power Spectrum in Expanding Dipolar Condensates
Seok-Yeong Chä and Uwe R. Fischer
arXiv:1609.06155v1 [cond-mat.quant-gas] (2016).
How precisely can the speed of light and the metric of space-time be determined in principle?
Daniel Braun, Fabienne Schneiter and Uwe R. Fischer
arXiv:1502.04979v2 [quant-ph] (2016).
Amplification of the quantum superposition macroscopicity of a flux qubit by a magnetized Bose gas
T. J. Volkoff and Uwe R. Fischer
Phys. Rev. A 94, 042320 (2016).
Quantum sine-Gordon dynamics on analogue curved spacetime in a weakly imperfect scalar Bose gas
T. J. Volkoff and Uwe R. Fischer
Phys. Rev. D 94, 024051 (2016).

2015

"Photonic" Cat States from Strongly Interacting Matter Waves
Uwe R. Fischer and Myung-Kyun Kang
Phys. Rev. Lett. 115, 260404 (2015).
Condensate fragmentation as a sensitive measure of the quantum many-body behavior of bosons with long-range interactions
Uwe R. Fischer, Axel U. J. Lode, and Budhaditya Chatterjee
Phys. Rev. A 91, 063621 (2015).

2014

Consistent perturbative treatment of the subohmic spin-boson model yielding arbitrarily small $T_2/T_1$ decoherence time ratios
Kyung-Joo Noh and Uwe R. Fischer
Phys. Rev. B 90, 220302 (Rapid Communication) (2014).
Revealing Single-Trap Condensate Fragmentation by Measuring Density-Density Correlations after Time of Flight
Myung-Kyun Kang and Uwe R. Fischer
Phys. Rev. Lett. 113, 140404 (2014).
Universality of the Berezinskii–Kosterlitz–Thouless type of phase transition in the dipolar XY-model
A. Yu. Vasiliev, A. E. Tarkhov, L. I. Menshikov, P. O. Fedichev, and Uwe R. Fischer
New J. Phys. 16, 053011 (2014).
Truncated many-body dynamics of interacting bosons: A variational principle with error monitoring
Kang-Soo Lee and Uwe R. Fischer
Int. J. Mod. Phys. B 28, 1550021 (2014).

2013

Ultrafast quantum random access memory utilizing single Rydberg atoms in a Bose-Einstein condensate
Kelly R. Patton and Uwe R. Fischer
Phys. Rev. Lett. 111, 024504 (2013).
Robustness of fragmented condensate many-body states for continuous distribution amplitudes in Fock space
Uwe R. Fischer and Bo Xiong
Phys. Rev. A 88, 053602 (2013).
Transfer and storage of qubits in the presence of decoherence
Kelly R. Patton and Uwe R. Fischer
EPL 102, 20001 (2013).
Interaction-induced coherence among polar bosons stored in triple-well potentials
Bo Xiong and Uwe R. Fischer
Phys. Rev. A 88, 063608 (2013).
Stability of spherically trapped three-dimensional Bose-Einstein condensates against macroscopic fragmentation
Philipp Bader and Uwe R. Fischer
Phys. Rev. A 87, 023632 (2013).
Hybrid of superconducting quantum interference device and atomic Bose-Einstein condensate: An architecture for quantum information processing
Kelly R. Patton and Uwe R. Fischer
Phys. Rev. A 87, 052303 (2013).

2012

Verifying the observer dependence of quasiparticle counts in the analogue gravity of dilute ultracold quantum gases
Uwe R. Fischer
arXiv:1205.5548 [cond-mat.quant-gas] (2012).
Identifying strongly correlated supersolid states on the optical lattice by quench-induced $\pi$-states
Uwe R. Fischer and Bo Xiong
EPL 99, 66003 (2012).

2011

Many-site coherence revivals in the extended Bose-Hubbard model and the Gutzwiller approximation
Uwe R. Fischer and Bo Xiong
Phys. Rev. A 84, 063635 (2011).
Emergence of a new pair-coherent phase in many-body quenches of repulsive bosons
Uwe R. Fischer, Kang-Soo Lee, and Bo Xiong
Phys. Rev. A 84, 011604 (Rapid Communication) (2011).

2010

System size scaling of topological defect creation in a second-order dynamical quantum phase transition
Michael Uhlmann, Ralf Schützhold, and Uwe R. Fischer
New J. Phys. 12, 095020 (2010).
Interacting trapped bosons yield fragmented condensate states in low dimensions
Uwe R. Fischer and Philipp Bader
Phys. Rev. A 82, 013607 (2010).
Increased Cation Conductance in Human Erythrocytes Artificially Aged by Glycation
Yuliya V. Kucherenko, Shefalee K. Bhavsar, Valentin I. Grischenko, Uwe R. Fischer, Stephan M. Huber, and Florian Lang
J. Membrane Biol. 235, 177-189 (2010).
$O(N)$ symmetry-breaking quantum quench: Topological defects versus quasiparticles
Michael Uhlmann, Ralf Schützhold, and Uwe R. Fischer
Phys. Rev. D 81, 025017 (2010).

2009

Fragmented many-body ground states for scalar bosons in a single trap
Philipp Bader and Uwe R. Fischer
Phys. Rev. Lett. 103, 060402 (2009).

Before 2009

2008

Tunneling-induced damping of phase coherence revivals in deep optical lattices
Uwe R. Fischer and Ralf Schützhold
Phys. Rev. A 78, 061603 (Rapid Communication) (2008).
Effect of fluctuations on the superfluid-supersolid phase transition on the lattice
Ralf Schützhold, Michael Uhlmann, and Uwe R. Fischer
Phys. Rev. A 78, 033604 (2008).
Bogoliubov theory of quantum correlations in the time-dependent Bose-Hubbard model
Uwe R. Fischer, Ralf Schützhold, and Michael Uhlmann
Phys. Rev. A 77, 043615 (2008).
Coherent single atom shuttle between two Bose-Einstein condensates
Uwe R. Fischer, Christian Iniotakis, and Anna Posazhennikova
Phys. Rev. A 77, 031602 (Rapid Communication) (2008).

2007

Vortex quantum creation and winding number scaling in a quenched spinor Bose gas
Michael Uhlmann, Ralf Schützhold, and Uwe R. Fischer
Phys. Rev. Lett. 99, 120407 (2007).
Quantum top inside a Bose-Einstein-condensate Josephson junction
Ingrid Bausmerth, Uwe R. Fischer, and Anna Posazhennikova
Phys. Rev. A 75, 053605 (2007).
Dynamical Aspects of Analogue Gravity: The Backreaction of Quantum Fluctuations in Dilute Bose-Einstein Condensates
Uwe R. Fischer
Lect. Notes Phys. 718, 93-113 (2007).

2006

Global singularity-free solution of the Iordanskiĭ force problem
Markus Flaig and Uwe R. Fischer
Phys. Rev. B 74, 224503 (2006).
Sweeping from the superfluid to the Mott phase in the Bose-Hubbard model
Ralf Schützhold, Michael Uhlmann, Yan Xu, and Uwe R. Fischer
Phys. Rev. Lett. 97, 200601 (2006).
Mean-field expansion in Bose-Einstein condensates with finite-range interactions
Ralf Schützhold, Michael Uhlmann, Yan Xu, and Uwe R. Fischer
Int. J. Mod. Phys. B 20, 3555-3565 (2006).
Stability of quasi-two-dimensional Bose-Einstein condensates with dominant dipole-dipole interactions
Uwe R. Fischer
Phys. Rev. A 73, 031602 (Rapid Communication) (2006).

2005

Quantum backreaction in dilute Bose-Einstein condensates
Ralf Schützhold, Michael Uhlmann, Yan Xu, and Uwe R. Fischer
Phys. Rev. D 72, 105005 (2005).
Reply to Comment on "Dynamical role of anyonic excitation statistics in rapidly rotating Bose gases"
Uwe R. Fischer
Phys. Rev. Lett. 94, 208904 (2005).
Maximal length of trappped one-dimensional Bose-Einstein condensates
Uwe R. Fischer
J. Low Temp. Phys. 138, 723-728 (2005).

2004

Quantum simulation of cosmic inflation in two-component Bose-Einstein condensates
Uwe R. Fischer and Ralf Schützhold
Phys. Rev. A 70, 063615 (2004).
Dynamical role of anyonic excitation statistics in rapidly rotating Bose gases
Uwe R. Fischer
Phys. Rev. Lett. 93, 160403 (2004).
Quasiparticle universes in Bose-Einstein condensates
Uwe R. Fischer
Mod. Phys. Lett. A 19, 1789-1812 (2004).
"Cosmological" quasiparticle production in harmonically trapped superfluid gases
Petr O. Fedichev and Uwe R. Fischer
Phys. Rev. A 69, 033602 (2004).
Observer dependence for the phonon content of the sound field living on the effective curved space-time background of a Bose-Einstein condensate
Petr O. Fedichev and Uwe R. Fischer
Phys. Rev. D 69, 064021 (2004).
Vortex liquids and vortex quantum Hall states in trapped rotating Bose gases
Uwe R. Fischer, Petr O. Fedichev, and Alessio Recati
J. Phys. B: At. Mol. Opt. Phys. 37, S301-S310 (2004).

2003

Zero-temperature damping of Bose-Einstein condensate oscillations by vortex-antivortex pair creation
Petr O. Fedichev, Uwe R. Fischer, and Alessio Recati
Phys. Rev. A 68, 011602 (Rapid Communication) (2003).
Gibbons-Hawking Effect in the Sonic de Sitter Space-Time of an Expanding Bose-Einstein-Condensed Gas
Petr O. Fedichev and Uwe R. Fischer
Phys. Rev. Lett. 91, 240407 (2003).
Warped space-time for phonons moving in a perfect nonrelativistic fluid
Uwe R. Fischer and Matt Visser
Europhys. Lett. 62, 1-7 (2003).
On the space-time curvature experienced by quasiparticle excitations in the Painlevé-Gullstrand effective geometry
Uwe R. Fischer and Matt Visser
Ann. Phys. (N.Y.) 304, 22-39 (2003).
Vortex states of rapidly rotating dilute Bose-Einstein condensates
Uwe R. Fischer and Gordon Baym
Phys. Rev. Lett. 90, 140402 (2003).

Before 2003

Existence of Long-Range Order for Trapped Interacting Bosons
Uwe R. Fischer
Phys. Rev. Lett. 89, 280402 (2002).
Riemannian geometry of irrotational vortex acoustics
Uwe R. Fischer and Matt Visser
Phys. Rev. Lett. 88, 110201 (2002).
Electromagnetomotive force fields in noninertial reference frames and accelerated superconducting quantum interferometers
Uwe R. Fischer, Christoph Häußler, Jörg Oppenländer, and Nils Schopohl
Phys. Rev. B 64, 214509 (2001).
Short wavelength spectrum and Hamiltonian stability of vortex rings
Uwe R. Fischer and Nils Schopohl
Phys. Rev. E 64, 016306 (2001).
Specific heat of the Kelvin modes in low temperature superfluid turbulence
Uwe R. Fischer
Phys. Rev. B 63, 212504 (2001).
Hall state quantization in a rotating frame
Uwe R. Fischer and Nils Schopohl
Europhys. Lett. 54, 502-507 (2001).
Thermal quasi-equilibrium states across Landau horizons in the effective gravity of superfluids
Uwe R. Fischer and Grigori E. Volovik
Int. J. Mod. Phys. D 10, 57-88 (2001).
Tunnelling of topological line defects in strongly coupled superfluids
Uwe R. Fischer
Ann. Phys. (Leipzig) 9, 523-570 (2000).
Motion of Quantized Vortices as Elementary Objects
Uwe R. Fischer
Ann. Phys. (N.Y.) 278, 62-85 (1999).
On the theory of vortex quantum tunnelling in the dense Bose superfluid helium II
Uwe R. Fischer
Physica B 255, 41-54 (1998).
Geometric Laws of Vortex Quantum Tunneling
Uwe R. Fischer
Phys. Rev. B 58, 105-108 (1998).
Massive Charged Strings in the Description of Vortex Ring Quantum Nucleation
Uwe R. Fischer
J. Low Temp. Phys. 110, 39-44 (1998).
Transition probabilities for a Rydberg atom in the field of a gravitational wave
Uwe R. Fischer
Class. Quantum Grav. 11, 463-474 (1994).