Periodic Reporting for period 1 - UltraComp (Unconventional Phases of Ultracold Quantum Matter with Competing Interactions)
Période du rapport: 2021-04-01 au 2023-03-31
The goal of the project Unconventional Phases of Ultracold Quantum Matter with Competing Interactions (UltraComp) was to explore new phases of matter originating from the interplay between inter-particle interactions with either kinetic energy (modified by an externally imposed coupling between the particle’s spin and its momentum) or with intrinsic quantum fluctuations. The competition between these interactions could give rise to new and exotic phases with seemingly contradictory features. One such example is the supersolid, a material which can flow without friction as a superfluid while keeping a periodic structure as a crystal.
The objectives of this project were: (1) to create a supersolid in a spin-orbit coupled Bose-Einstein condensate and explore its properties. (2) to unite the characteristics of the novel supersolid with a quantum droplet, an exotic system stabilized from collapse by quantum fluctuations, to investigate a never seen phase: the supersolid-striped droplet.
The importance of this research lies in understanding nature and how the interplay between different energies can give rise to phases of matter with very different and sometimes seemingly contradictory properties. The experimental study of these phases has been a goal for over 50 years [A. F. Andreev and I. M. Lifshitz, Sov. Phys. JETP 29, 1107 (1969), A. J. Leggett, Phys. Rev. Lett. 25, 1543 (1970)], and it is only recently that we have been able to study these phases and compare them across different experimental platforms.
The objectives of this project were: (1) to create a supersolid in a spin-orbit coupled Bose-Einstein condensate and explore its properties. (2) to unite the characteristics of the novel supersolid with a quantum droplet, an exotic system stabilized from collapse by quantum fluctuations, to investigate a never seen phase: the supersolid-striped droplet.
The importance of this research lies in understanding nature and how the interplay between different energies can give rise to phases of matter with very different and sometimes seemingly contradictory properties. The experimental study of these phases has been a goal for over 50 years [A. F. Andreev and I. M. Lifshitz, Sov. Phys. JETP 29, 1107 (1969), A. J. Leggett, Phys. Rev. Lett. 25, 1543 (1970)], and it is only recently that we have been able to study these phases and compare them across different experimental platforms.
During the duration of the project, we have investigated a novel phase of matter known as supersolid. We have created this phase by using light to couple a pair of internal states in a Bose-Einstein condensate, which allowed us to modify the dispersion relation of the resulting dressed states. In this regime, instead of the parabolic dispersion relation of a free particle, the modified dispersion relation takes the form of a double well. If the system populates these wells in momentum space, then in position space, this gives rise to atomic density modulation due to the interference between different momentum states. This crystal-like density modulation and the superfluidity of a Bose-Einstein condensate give rise to the supersolid phase.
We have observed the submicron density modulation in a light-coupled supersolid for the first time using a novel technique using matter-wave optics to magnify the atomic distribution. Moreover, we have explored the configuration space where the formation of the supersolid is possible by adjusting the strength of the light coupling, and we have observed a good quantitative agreement between our measurements and the mixture model, a low-energy model we have developed for this system. Finally, we have shown that the modulation period in the supersolid is not fixed and can depend on the momentum of the atoms and the light-coupling strength, indicating that the light-coupled supersolid is not stiff.
Finally, in an experiment not planned in the initial proposal, we have implemented a condensed-matter topological gauge theory in the continuum for the first time. The quantum simulation of gauge theories is an exciting field which only until recently has become possible due to the exquisite control of internal and external degrees of freedom in ultracold atoms. We have realized this feature by light dressing a Bose mixture in the high coupling regime together with tunable atomic interactions. We have engineered a system which maps to a one-dimensional reduction of the Chern-Simons gauge theory, which provides a low-energy description of the fractional quantum Hall states. In our experiment, we have measured the two main observables of this gauge theory: a density-dependent electric field and chiral solitons (wavepackets that propagate without dispersion only in a particular direction).
We have observed the submicron density modulation in a light-coupled supersolid for the first time using a novel technique using matter-wave optics to magnify the atomic distribution. Moreover, we have explored the configuration space where the formation of the supersolid is possible by adjusting the strength of the light coupling, and we have observed a good quantitative agreement between our measurements and the mixture model, a low-energy model we have developed for this system. Finally, we have shown that the modulation period in the supersolid is not fixed and can depend on the momentum of the atoms and the light-coupling strength, indicating that the light-coupled supersolid is not stiff.
Finally, in an experiment not planned in the initial proposal, we have implemented a condensed-matter topological gauge theory in the continuum for the first time. The quantum simulation of gauge theories is an exciting field which only until recently has become possible due to the exquisite control of internal and external degrees of freedom in ultracold atoms. We have realized this feature by light dressing a Bose mixture in the high coupling regime together with tunable atomic interactions. We have engineered a system which maps to a one-dimensional reduction of the Chern-Simons gauge theory, which provides a low-energy description of the fractional quantum Hall states. In our experiment, we have measured the two main observables of this gauge theory: a density-dependent electric field and chiral solitons (wavepackets that propagate without dispersion only in a particular direction).
The work carried out in this project has laid the foundations for the study of the supersolid-stripe droplet, which will be pursued by the group in the future. Importantly, the project has led to two exciting scientific results: the creation, observation and exploration of the light-induced supersolid for which a manuscript with the findings is under preparation, and the simulation of a condensed-matter gauge theory in the continuum, which has led to two high-impact journal publications: A. Frölian et al., Nature 608, 293 (2022) and C. S. Chisholm et al., Phys. Rev. Research 4, 043088 (2022) (selected as Editor’s suggestion).
I have presented these results at two national and six international conferences, such as ICAP and DAMOP. In addition, I have mentored two PhD students, and I was the thesis co-supervisor of a Master’s student and the supervisor of two bachelor students during the duration of the project.
The dissemination of the project was done through outreach activities and social media. On social media, the results were shared on the group’s website (http://www.qge.icfo.es/(s’ouvre dans une nouvelle fenêtre)) and twitter account (@icfo_QGE), and the host institution’s twitter account (@ICFOnians) and LinkedIn profile (@ICFO). Also, the publications supported by this action were covered by popular science dissemination websites such as Phys.Org EurekaAlert! and IFLscience. Moreover, I participated in outreach activities at the host institution (ICFO) aimed at high-school, bachelor and graduate students. I also volunteered at a local community centre teaching science, programming, and doing lab tours for children at risk of social exclusion.
I have presented these results at two national and six international conferences, such as ICAP and DAMOP. In addition, I have mentored two PhD students, and I was the thesis co-supervisor of a Master’s student and the supervisor of two bachelor students during the duration of the project.
The dissemination of the project was done through outreach activities and social media. On social media, the results were shared on the group’s website (http://www.qge.icfo.es/(s’ouvre dans une nouvelle fenêtre)) and twitter account (@icfo_QGE), and the host institution’s twitter account (@ICFOnians) and LinkedIn profile (@ICFO). Also, the publications supported by this action were covered by popular science dissemination websites such as Phys.Org EurekaAlert! and IFLscience. Moreover, I participated in outreach activities at the host institution (ICFO) aimed at high-school, bachelor and graduate students. I also volunteered at a local community centre teaching science, programming, and doing lab tours for children at risk of social exclusion.