


2018-01-23
NOSLEN SUAREZ
NOSLEN SUAREZ

2018-02-22
VALERIA RODRÍGUEZ-FAJARDO
VALERIA RODRÍGUEZ-FAJARDO

2018-02-26
BENJAMIN WOLTER
BENJAMIN WOLTER

2018-03-19
JOANNA ZIELINSKA
JOANNA ZIELINSKA

2018-03-23
QUAN LIU
QUAN LIU

2018-03-28
LARA LAPARRA
LARA LAPARRA

2018-04-03
GUILLAUME CORDIER
GUILLAUME CORDIER

2018-05-22
KEVIN SCHÄDLER
KEVIN SCHÄDLER

2018-06-14
MIRIAM MARCHENA
MIRIAM MARCHENA

2018-06-19
CARLOS ABELLAN
CARLOS ABELLAN

2018-07-02
LUKAS NEUMEIER
LUKAS NEUMEIER

2018-07-24
SHAHRZAD PARSA
SHAHRZAD PARSA

2018-07-25
PAU FARRERA
PAU FARRERA

2018-07-31
BARBARA BUADES
BARBARA BUADES

2018-09-06
SIMON COOP
SIMON COOP

2018-09-13
NICOLAS MARING
NICOLAS MARING

2018-09-19
IVAN SUPIC
IVAN SUPIC

2018-10-02
ANIELLO LAMPO
ANIELLO LAMPO

2018-10-10
CÉSAR CABRERA
CÉSAR CABRERA

2018-10-11
FLORIAN CURCHOD
FLORIAN CURCHOD

2018-10-18
JOSEP CANALS
JOSEP CANALS

2018-10-19
ROLAND TERBORG
ROLAND TERBORG

2018-10-22
KAVITHA KALAVOOR
KAVITHA KALAVOOR

2018-10-24
MIGUEL MIRELES
MIGUEL MIRELES

2018-10-26
KYRA BORGMAN
KYRA BORGMAN

2018-10-30
JOSE M. GARCIA-GUIRADO
JOSE M. GARCIA-GUIRADO

2018-11-12
JIL SCHWENDER
JIL SCHWENDER

2018-12-10
JOSÉ RAMÓN MARTÍNEZ
JOSÉ RAMÓN MARTÍNEZ

2018-12-12
LIJUN MENG
LIJUN MENG

2018-12-17
NICOLÁS MORELL
NICOLÁS MORELL

2018-12-18
JUNXIONG WEI
JUNXIONG WEI
Quantum Liquid Droplets in a mixture of Bose-Einstein Condensates


CESAR CABRERA
October 10th, 2018
CÉSAR CABRERA
Ultracold Quantum Gases
ICFO-The Institute of Photonic Sciences
In this thesis, we report on the design and construction of a quantum simulator experiment using quantum gases in Spain. This experiment exploits mixtures of the three isotopes of potassium, which give access in an original approach to the study of Bose-Bose or Bose-Fermi mixtures using the same experimental setup. We validate our experimental setup with the observation of a Bose-Einstein condensate (BEC) of 41K and 39K. Moreover we observe the dual Bose-Einstein condensation of 39K–41K. These results represents the first observation of BECs in Spain and give access to a novel quantum degenerate mixture in the field. Since the control of interactions in our experiment are crucial, we characterize the scattering properties of the 39K–41K mixture, and spin mixtures of 39K and 41K. In addition, using a spin mixture of 39K BEC, we report on the observation of a novel state of matter: a composite quantum liquid droplet. This dilute quantum droplet is a liquid-like cluster of ultra-cold atoms self-trapped by attractive mean-field forces and stabilized against collapse by repulsive beyond mean-field many-body effects. This system follows the original proposal where D. Petrov predicted the formation of self-bound liquid droplets in mixtures of Bose-Einstein condensates. In the first series of experiments, we have observed the formation of quantum droplets in a regime where the Bose-Bose mixture should collapse from the mean-field perspective.We directly measure the droplet size and ultra-low density via high-resolution in situ imaging, and experimentally confirm their self-bound nature.We demonstrate that the existence of these droplets is a striking manifestation of quantum fluctuations. These droplets do not exist in single-component condensates with described with contact interactions. Finally, we observe that for small atom numbers, quantum pressure dissociates the droplets and drives a liquid-to-gas transition, which we map out as a function of interaction strength. These measurements open an intriguing point of investigation: the difference existing between droplets and bright solitons. In the second series of experiments, we address it by placing the mixture in an optical waveguide, realizing a system that contains both composite bright solitons and quantum liquid droplets. In analogy to non-linear optics, the former can be seen as one-dimensional matter-wave solitons stabilized by dispersion, whereas the latter corresponds to highdimensional solitons stabilized by a higher order non-linearity. We find that depending on atom number, interaction strength and confinement, solitons and droplets can be smoothly connected or remain distinct states coexisting only in a bi-stable region. We measure their spin composition, extract their density for a broad range of parameters, and map out the boundary of the region separating solitons from droplets. Our experiments demonstrate a novel type of ultra-dilute quantum liquid, stabilized only by contact interactions. They provide an ideal platform for benchmarking complex quantum many-body theories beyond the mean-field approximation in a quantum simulation approach. Furthermore, they constitute a novel playground to explore experimentally self-bound states stabilized by unconventional higher order nonlinearities, relevant in non-linear optics.
Wednesday, October 10, 11:00. ICFO Auditorium
Thesis Advisor: Prof Dr Leticia Tarruell
ICFO-The Institute of Photonic Sciences
In this thesis, we report on the design and construction of a quantum simulator experiment using quantum gases in Spain. This experiment exploits mixtures of the three isotopes of potassium, which give access in an original approach to the study of Bose-Bose or Bose-Fermi mixtures using the same experimental setup. We validate our experimental setup with the observation of a Bose-Einstein condensate (BEC) of 41K and 39K. Moreover we observe the dual Bose-Einstein condensation of 39K–41K. These results represents the first observation of BECs in Spain and give access to a novel quantum degenerate mixture in the field. Since the control of interactions in our experiment are crucial, we characterize the scattering properties of the 39K–41K mixture, and spin mixtures of 39K and 41K. In addition, using a spin mixture of 39K BEC, we report on the observation of a novel state of matter: a composite quantum liquid droplet. This dilute quantum droplet is a liquid-like cluster of ultra-cold atoms self-trapped by attractive mean-field forces and stabilized against collapse by repulsive beyond mean-field many-body effects. This system follows the original proposal where D. Petrov predicted the formation of self-bound liquid droplets in mixtures of Bose-Einstein condensates. In the first series of experiments, we have observed the formation of quantum droplets in a regime where the Bose-Bose mixture should collapse from the mean-field perspective.We directly measure the droplet size and ultra-low density via high-resolution in situ imaging, and experimentally confirm their self-bound nature.We demonstrate that the existence of these droplets is a striking manifestation of quantum fluctuations. These droplets do not exist in single-component condensates with described with contact interactions. Finally, we observe that for small atom numbers, quantum pressure dissociates the droplets and drives a liquid-to-gas transition, which we map out as a function of interaction strength. These measurements open an intriguing point of investigation: the difference existing between droplets and bright solitons. In the second series of experiments, we address it by placing the mixture in an optical waveguide, realizing a system that contains both composite bright solitons and quantum liquid droplets. In analogy to non-linear optics, the former can be seen as one-dimensional matter-wave solitons stabilized by dispersion, whereas the latter corresponds to highdimensional solitons stabilized by a higher order non-linearity. We find that depending on atom number, interaction strength and confinement, solitons and droplets can be smoothly connected or remain distinct states coexisting only in a bi-stable region. We measure their spin composition, extract their density for a broad range of parameters, and map out the boundary of the region separating solitons from droplets. Our experiments demonstrate a novel type of ultra-dilute quantum liquid, stabilized only by contact interactions. They provide an ideal platform for benchmarking complex quantum many-body theories beyond the mean-field approximation in a quantum simulation approach. Furthermore, they constitute a novel playground to explore experimentally self-bound states stabilized by unconventional higher order nonlinearities, relevant in non-linear optics.
Wednesday, October 10, 11:00. ICFO Auditorium
Thesis Advisor: Prof Dr Leticia Tarruell