Final Report Summary - ATOMIC MIXTURES (Quantum phases of Fermi-Fermi, Bose-Bose and Bose-Fermi mixtures of atomic gases at ultracold temperatures)
Dr. Menderes Iskin, the researcher in charge of the project EU-FP7-PIRG07-GA-2010-268239 (acronym Atomic Mixtures), wishes to express his gratitude to the Commission for their support on his research.
1.1. Project Objectives: In this project, Dr. Iskin suggested to work on four major problems in the field of condensed atomic and molecular physics. The problems are briefly described below.
(1) Atomic Fermi-Fermi mixtures: investigation of the fate of Fulde-Ferrel-Larkin-Ovchinnikov (FFLO)-type spatially modulated superfluid and topologically-nontrivial superfluid phases, and their realization with imbalanced Fermi gases.
(2) Atomic Bose-Bose mixtures: investigation of the ground-state phase diagram of two-species Bose mixtures loaded onto optical lattices with a special emphasis on the paired-superfluid phase and its realization.
(3) Light atom-Heavy atom mixtures: investigation of the fate of supersolid-like phases and their realization with quantum gas mixtures.
(4) Heteronuclear molecules: investigation of the possibility of ferroelectric superfluidity and its realization in a Bose-Einstein condensate (BEC) of heteronuclear molecules.
1.2. Work Performed and Main Results: Dr. Iskin has made substantial progress on the objectives (1), (2) and (3), and he is still working on related problems. Most of his results have been published as 18 articles in high-impact physics journals and 2 articles in local popular magazines, and the details of some of these results are briefly summarized below.
(1) Some of the most significant (in terms of citation impact) results of this project are obtained in Phys. Rev. Lett. 107, 050402 (2011) and its longer version Phys. Rev. A 84, 043621 (2011), for the ground-state phase diagram of spin-orbit coupled uniform Fermi gases. Dr. Iskin has shown that the spin-orbit coupling (SOC) gives rise to topologically-nontrivial and thermodynamically-stable gapless superfluid phases when the pseudo-spin populations of an atomic Fermi gas is imbalanced, with the possibility of featuring Majorana zero-energy quasiparticles which are the key elements in fault-tolerant quantum computing. The vortex core states of these systems have been analyzed in Phys. Rev. A 85, 013622 (2012), showing that the signatures for the appearance of core- and edge-bound states can be directly found in the density of single-particle states and particle-current density. The effects of in-plane Zeeman field have also been studied in Phys. Rev. A 87, 063627 (2013) and Phys. Rev. A 88, 013631 (2013), showing that FFLO-type superfluid phase is highly favored against the uniformly polarized superfluid one and may be studied in such an atomic setting.
(2) Another one of the most important results is obtained in Phys. Rev. A 83, 051606(R) (2011), for the ground-state phase diagram of the extended Bose-Hubbard (BH) model. In the case of weak nearest-neighbor interaction, it is well known that the ground state alternates between the charge-density-wave and Mott insulators, and the supersolid phase occupies small regions around the charge-density-wave insulators. However, when the nearest-neighbor interaction becomes strong enough, Dr. Iskin has showed that the ground state has only charge-density-wave insulators, and more importantly, the supersolid phase occupies a much larger region in the phase diagram, existing up to very large hopping values, which could be orders of magnitude higher than that of the well-known case. These predictions have recently been confirmed by numerically exact Quantum Monte Carlo calculations, suggesting a promising route towards observing a supersolid phase for the very first time without any controversy.
(3) The third significant result is obtained for the ground-state phase diagram of the two-species BH model. Dr. Iskin has carried the strong-coupling expansion out to third-order in the hopping in Phys. Rev. A 82, 033630 (2010), and performed a scaling analysis using the known critical behavior at the tip of the insulating lobes, allowing him to accurately predict the shape of the insulating lobes. In addition, by restricting the model Hamiltonian to the subspace of paired particles in Phys. Rev. A 82, 055601 (2010), he has been able to derive an analytic expression for the Mott insulator-paired superfluid transition boundary. In a more recent work, the effects of both the strength and symmetry of SOC have been studied in Phys. Rev. A 89, 043603 (2014), showing that the superfluid phase is twisted with its phase (but not the magnitude) of the complex order parameter modulating from site to site. Such a twisted superfluid phase has never been observed before.
(4) Lastly, Dr. Iskin have also studied the ultracold neutral fermion superfluids in the presence of fictitious magnetic fields and charged fermion superfluids in the presence of real magnetic fields. It is well known that the charged fermion superfluids undergo a phase transition from type-I to type-II superfluidity, where the magnetic properties of the superfluid change from being a perfect diamagnet without vortices to a partial diamagnet with the emergence of the Abrikosov vortex lattice. In Phys. Rev. A 83, 045602 (2011), Dr. Iskin has obtained the universal phase diagram for the transition from type-I to type-II superfluidity in the Bardeen-Cooper-Schrieffer (BCS)-BEC crossover, which can be tuned by changing the scattering parameter (interaction) for fixed density. In a more recent work, the ground-state phase diagram of the single-band attractive Hofstadter-Hubbard model has been explored in arXiv:1406.6890 (2014), where it is shown that the interplay between the Hofstadter butterfly and superfluidity breaks translational symmetry, giving rise to stripe-ordered superfluid, supersolid and vortex lattice phases in large parameter spaces. The supersolid-like phases are of high-demand in condensed-matter, nuclear and elementary-particle physics, and this work points an alternative promising direction towards creating them with cold atoms.
1.3. Publications and Preprints:
(1) M. Iskin, "Stripe-ordered superfluid, supersolid and vortex lattice phases in attractive Hofstadter-Hubbard Model"; arXiv:1406.6890 (2014).
(2) A. T. Bolukbasi and M. Iskin, "Superfluid-Mott insulator transition in spin-orbit coupled Bose-Hubbard Model"; Phys. Rev. A 89, 043603 (2014).
(3) M. Iskin, "Superfluid phases of ultracold Fermi gases on a checkerboard superlattice"; Phys. Rev. A 88, 053606 (2013).
(4) M. Iskin, "Spin-orbit coupling induced Fulde-Ferrell-Larkin-Ovchinnikov-like Cooper pairing and skyrmion-like polarization textures in optical lattices"; Phys. Rev. A 88, 013631 (2013)
(5) M. Iskin and A. L. Subasi, "Topological superfluid phases of an atomic Fermi gas with in- and out-of-plane Zeeman fields and equal Rashba-Dresselhaus spin-orbit coupling"; Phys. Rev. A 87, 063627 (2013).
(6) M. Iskin, "Trapped Fermi gases with Rashba spin-orbit coupling in two dimensions"; Phys. Rev. A 86, 065601 (2012).
(7) M. Iskin, "Asiri soguga hakim olmak ama neden?"; Koç University Fener Magazine (Fall 2012) in Turkish.
(8) M. Iskin, "Mastering the Ultracold"; Koç University Frontiers Magazine (Fall 2012).
(9) E. Doko, A. L. Subasi, and M. Iskin, "Counterflow of spontaneous mass currents in trapped spin-orbit coupled Fermi gases"; Phys. Rev. A 85, 053634 (2012).
(10) M. Iskin, "Vortex line in spin-orbit coupled atomic Fermi gases"; Phys. Rev. A 85, 013622 (2012).
(11) M. Iskin and A. L. Subasi, "Quantum phases of atomic Fermi gases with anisotropic spin-orbit coupling"; Phys. Rev. A 84, 043621 (2011).
(12) M. Iskin and A. L. Subasi, "Mass-imbalanced Fermi gases with spin-orbit coupling"; Phys. Rev. A 84, 041610(R) (2011).
(13) M. Iskin and A. L. Subasi Subasi, "Stability of spin-orbit coupled Fermi gases with population imbalance"; Phys. Rev. Lett. 107, 050402 (2011).
(14) M. Iskin, "Route to supersolidity for the extended Bose-Hubbard model"; Phys. Rev. A 83, 051606(R) (2011).
(15) M. Iskin, "Artifical gauge fields for the Bose-Hubbard model on a checkerboard superlattice and extended Bose-Hubbard model"; Eur. Phys. J. B 85, 76 (2012).
(16) M. Iskin, "Mean-field theory for the Mott insulator-paired superfluid transition in the two-species Bose-Hubbard model"; Phys. Rev. A 82, 055601 (2010).
(17) M. Iskin, "Isothermal-sweep theorems for ultracold quantum gases in a canonical ensemble"; Phys. Rev. A 83, 033613 (2011).
(18) M. Iskin and A. L. Subasi, "Cooper pairing and BCS-BEC evolution in mixed dimensional Fermi gases"; Phys. Rev. A 82, 063628 (2010).
(19) M. Iskin and C. A. R. Sa de Melo, "Ultracold fermions in real or fictitious magnetic fields: BCS-BEC evolution and type-I--type-II transition"; Phys. Rev. A 83, 045602 (2011).
(20) M. Iskin, "Strong-coupling expansion for the two-species Bose-Hubbard model"; Phys. Rev. A 82, 033630 (2010).
1.4. Expected Final Results and Potential Impact: Following the completion of this project, Dr. Iskin will continue working on the many-body phases of strongly-correlated ultracold mixtures of Fermi and Bose gases. In particular, he is planning to study the interplay between the in-plane and out-of-plane Zeeman fields and gauge fields in both Fermi-Fermi and Bose-Bose mixtures, and further explore the fate of FFLO-type superfluid and/or supersolid phases in these systems. For instance, Dr. Iskin has already started working on the ground-state phase diagram of the single-band attractive Hofstadter-Hubbard model on a square lattice, and has found substantial evidence in his most recent preprint arXiv:1406.6890 (2014) that the interplay between the Hofstadter butterfly and superfluidity breaks translational symmetry, giving rise to stripe-ordered superfluid, supersolid and vortex lattice phases in large parameter spaces. Given that FFLO-like supersolid phases are of high-demand in condensed-matter, nuclear and elementary-particle physics, this finding suggests a promising route towards creating them by loading neutral atomic Fermi gases on laser-induced optical lattices under laser-induced gauge fields.
As for the potential impact of the project, it should be noted that this grant has helped Dr. Iskin to successfully integrate to his new environment very quickly; it has enabled him to travel many places and interact with many researchers. He has already received 5 prestigious national awards and 1 university-wide award for his research that is performed during the integration period, and obtained the YOK Docent title (equivalent of a tenure) from the Turkish Council of Higher Education. It has also enabled him to give many talks and attend many workshops in Turkey, to transfer the knowledge to host, and to attract the attention of promising students in Turkey.
In particular, Dr. Iskin is using all the means possible to introduce and promote his field of expertise, i.e. ultracold atomic physics, to the scientific community of the host country. Since this field is relatively new to this community, there are only a few active researchers working on it. For instance, Dr. Iskin has participated in the summer schools and workshops that are organized in ITAP (Turunc, Turkey), which are geared primarily for graduate students and postdoctoral fellows but exceptional senior undergraduates were also highly encouraged to attend. As a result of these efforts, Dr. Iskin’s research group has grown considerably in the past 4 years, currently consisting of 5 principal members (in addition to a recently graduated MS student): 1 Asst. Prof. (a former postdoc), 2 post-PhD researchers (both recruited from European institutions), and 2 PhD candidates (recruited from national universities).
In addition, as of January 2014, the Scientific and Technological Research Council of Turkey (TUBITAK) has appointed Dr. Iskin to the Turkish Physics Olympiad Team Recruitment Committee. He has already organized several training camps for the selected high schools students from all over Turkey, and attended 2014 Olympics as the team leader in Astana, Kazakhstan. Since this organization provides an excellent opportunity to expose the top science and/or engineering oriented students of Turkey to physics research in general, and as early as at the high school level, he is already committed for the 2015 Olympics and very keen on participating in this outreach program in the upcoming years to promote his research interests. Lastly, Dr. Iskin has written two popular magazine articles for the Koc University’s annual FENER and FRONTIERS magazines, both of which have a very broad audience in Turkey including most of the universities, national institutes and research centers from all around Turkey. They are also sent to R&D departments of 98 consolidated companies of the Koc corporate. Both of these articles appeared in the Fall 2012 issues, and they have allowed Dr. Iskin to introduce his expertise in cold atom physics to a much broader audience outside of academia.
1.5. Project Website: The details of the project and related material (group members, funding agencies, published and unpublished articles, etc.) can be found in the group webpage http://home.ku.edu.tr/~miskin/
1.1. Project Objectives: In this project, Dr. Iskin suggested to work on four major problems in the field of condensed atomic and molecular physics. The problems are briefly described below.
(1) Atomic Fermi-Fermi mixtures: investigation of the fate of Fulde-Ferrel-Larkin-Ovchinnikov (FFLO)-type spatially modulated superfluid and topologically-nontrivial superfluid phases, and their realization with imbalanced Fermi gases.
(2) Atomic Bose-Bose mixtures: investigation of the ground-state phase diagram of two-species Bose mixtures loaded onto optical lattices with a special emphasis on the paired-superfluid phase and its realization.
(3) Light atom-Heavy atom mixtures: investigation of the fate of supersolid-like phases and their realization with quantum gas mixtures.
(4) Heteronuclear molecules: investigation of the possibility of ferroelectric superfluidity and its realization in a Bose-Einstein condensate (BEC) of heteronuclear molecules.
1.2. Work Performed and Main Results: Dr. Iskin has made substantial progress on the objectives (1), (2) and (3), and he is still working on related problems. Most of his results have been published as 18 articles in high-impact physics journals and 2 articles in local popular magazines, and the details of some of these results are briefly summarized below.
(1) Some of the most significant (in terms of citation impact) results of this project are obtained in Phys. Rev. Lett. 107, 050402 (2011) and its longer version Phys. Rev. A 84, 043621 (2011), for the ground-state phase diagram of spin-orbit coupled uniform Fermi gases. Dr. Iskin has shown that the spin-orbit coupling (SOC) gives rise to topologically-nontrivial and thermodynamically-stable gapless superfluid phases when the pseudo-spin populations of an atomic Fermi gas is imbalanced, with the possibility of featuring Majorana zero-energy quasiparticles which are the key elements in fault-tolerant quantum computing. The vortex core states of these systems have been analyzed in Phys. Rev. A 85, 013622 (2012), showing that the signatures for the appearance of core- and edge-bound states can be directly found in the density of single-particle states and particle-current density. The effects of in-plane Zeeman field have also been studied in Phys. Rev. A 87, 063627 (2013) and Phys. Rev. A 88, 013631 (2013), showing that FFLO-type superfluid phase is highly favored against the uniformly polarized superfluid one and may be studied in such an atomic setting.
(2) Another one of the most important results is obtained in Phys. Rev. A 83, 051606(R) (2011), for the ground-state phase diagram of the extended Bose-Hubbard (BH) model. In the case of weak nearest-neighbor interaction, it is well known that the ground state alternates between the charge-density-wave and Mott insulators, and the supersolid phase occupies small regions around the charge-density-wave insulators. However, when the nearest-neighbor interaction becomes strong enough, Dr. Iskin has showed that the ground state has only charge-density-wave insulators, and more importantly, the supersolid phase occupies a much larger region in the phase diagram, existing up to very large hopping values, which could be orders of magnitude higher than that of the well-known case. These predictions have recently been confirmed by numerically exact Quantum Monte Carlo calculations, suggesting a promising route towards observing a supersolid phase for the very first time without any controversy.
(3) The third significant result is obtained for the ground-state phase diagram of the two-species BH model. Dr. Iskin has carried the strong-coupling expansion out to third-order in the hopping in Phys. Rev. A 82, 033630 (2010), and performed a scaling analysis using the known critical behavior at the tip of the insulating lobes, allowing him to accurately predict the shape of the insulating lobes. In addition, by restricting the model Hamiltonian to the subspace of paired particles in Phys. Rev. A 82, 055601 (2010), he has been able to derive an analytic expression for the Mott insulator-paired superfluid transition boundary. In a more recent work, the effects of both the strength and symmetry of SOC have been studied in Phys. Rev. A 89, 043603 (2014), showing that the superfluid phase is twisted with its phase (but not the magnitude) of the complex order parameter modulating from site to site. Such a twisted superfluid phase has never been observed before.
(4) Lastly, Dr. Iskin have also studied the ultracold neutral fermion superfluids in the presence of fictitious magnetic fields and charged fermion superfluids in the presence of real magnetic fields. It is well known that the charged fermion superfluids undergo a phase transition from type-I to type-II superfluidity, where the magnetic properties of the superfluid change from being a perfect diamagnet without vortices to a partial diamagnet with the emergence of the Abrikosov vortex lattice. In Phys. Rev. A 83, 045602 (2011), Dr. Iskin has obtained the universal phase diagram for the transition from type-I to type-II superfluidity in the Bardeen-Cooper-Schrieffer (BCS)-BEC crossover, which can be tuned by changing the scattering parameter (interaction) for fixed density. In a more recent work, the ground-state phase diagram of the single-band attractive Hofstadter-Hubbard model has been explored in arXiv:1406.6890 (2014), where it is shown that the interplay between the Hofstadter butterfly and superfluidity breaks translational symmetry, giving rise to stripe-ordered superfluid, supersolid and vortex lattice phases in large parameter spaces. The supersolid-like phases are of high-demand in condensed-matter, nuclear and elementary-particle physics, and this work points an alternative promising direction towards creating them with cold atoms.
1.3. Publications and Preprints:
(1) M. Iskin, "Stripe-ordered superfluid, supersolid and vortex lattice phases in attractive Hofstadter-Hubbard Model"; arXiv:1406.6890 (2014).
(2) A. T. Bolukbasi and M. Iskin, "Superfluid-Mott insulator transition in spin-orbit coupled Bose-Hubbard Model"; Phys. Rev. A 89, 043603 (2014).
(3) M. Iskin, "Superfluid phases of ultracold Fermi gases on a checkerboard superlattice"; Phys. Rev. A 88, 053606 (2013).
(4) M. Iskin, "Spin-orbit coupling induced Fulde-Ferrell-Larkin-Ovchinnikov-like Cooper pairing and skyrmion-like polarization textures in optical lattices"; Phys. Rev. A 88, 013631 (2013)
(5) M. Iskin and A. L. Subasi, "Topological superfluid phases of an atomic Fermi gas with in- and out-of-plane Zeeman fields and equal Rashba-Dresselhaus spin-orbit coupling"; Phys. Rev. A 87, 063627 (2013).
(6) M. Iskin, "Trapped Fermi gases with Rashba spin-orbit coupling in two dimensions"; Phys. Rev. A 86, 065601 (2012).
(7) M. Iskin, "Asiri soguga hakim olmak ama neden?"; Koç University Fener Magazine (Fall 2012) in Turkish.
(8) M. Iskin, "Mastering the Ultracold"; Koç University Frontiers Magazine (Fall 2012).
(9) E. Doko, A. L. Subasi, and M. Iskin, "Counterflow of spontaneous mass currents in trapped spin-orbit coupled Fermi gases"; Phys. Rev. A 85, 053634 (2012).
(10) M. Iskin, "Vortex line in spin-orbit coupled atomic Fermi gases"; Phys. Rev. A 85, 013622 (2012).
(11) M. Iskin and A. L. Subasi, "Quantum phases of atomic Fermi gases with anisotropic spin-orbit coupling"; Phys. Rev. A 84, 043621 (2011).
(12) M. Iskin and A. L. Subasi, "Mass-imbalanced Fermi gases with spin-orbit coupling"; Phys. Rev. A 84, 041610(R) (2011).
(13) M. Iskin and A. L. Subasi Subasi, "Stability of spin-orbit coupled Fermi gases with population imbalance"; Phys. Rev. Lett. 107, 050402 (2011).
(14) M. Iskin, "Route to supersolidity for the extended Bose-Hubbard model"; Phys. Rev. A 83, 051606(R) (2011).
(15) M. Iskin, "Artifical gauge fields for the Bose-Hubbard model on a checkerboard superlattice and extended Bose-Hubbard model"; Eur. Phys. J. B 85, 76 (2012).
(16) M. Iskin, "Mean-field theory for the Mott insulator-paired superfluid transition in the two-species Bose-Hubbard model"; Phys. Rev. A 82, 055601 (2010).
(17) M. Iskin, "Isothermal-sweep theorems for ultracold quantum gases in a canonical ensemble"; Phys. Rev. A 83, 033613 (2011).
(18) M. Iskin and A. L. Subasi, "Cooper pairing and BCS-BEC evolution in mixed dimensional Fermi gases"; Phys. Rev. A 82, 063628 (2010).
(19) M. Iskin and C. A. R. Sa de Melo, "Ultracold fermions in real or fictitious magnetic fields: BCS-BEC evolution and type-I--type-II transition"; Phys. Rev. A 83, 045602 (2011).
(20) M. Iskin, "Strong-coupling expansion for the two-species Bose-Hubbard model"; Phys. Rev. A 82, 033630 (2010).
1.4. Expected Final Results and Potential Impact: Following the completion of this project, Dr. Iskin will continue working on the many-body phases of strongly-correlated ultracold mixtures of Fermi and Bose gases. In particular, he is planning to study the interplay between the in-plane and out-of-plane Zeeman fields and gauge fields in both Fermi-Fermi and Bose-Bose mixtures, and further explore the fate of FFLO-type superfluid and/or supersolid phases in these systems. For instance, Dr. Iskin has already started working on the ground-state phase diagram of the single-band attractive Hofstadter-Hubbard model on a square lattice, and has found substantial evidence in his most recent preprint arXiv:1406.6890 (2014) that the interplay between the Hofstadter butterfly and superfluidity breaks translational symmetry, giving rise to stripe-ordered superfluid, supersolid and vortex lattice phases in large parameter spaces. Given that FFLO-like supersolid phases are of high-demand in condensed-matter, nuclear and elementary-particle physics, this finding suggests a promising route towards creating them by loading neutral atomic Fermi gases on laser-induced optical lattices under laser-induced gauge fields.
As for the potential impact of the project, it should be noted that this grant has helped Dr. Iskin to successfully integrate to his new environment very quickly; it has enabled him to travel many places and interact with many researchers. He has already received 5 prestigious national awards and 1 university-wide award for his research that is performed during the integration period, and obtained the YOK Docent title (equivalent of a tenure) from the Turkish Council of Higher Education. It has also enabled him to give many talks and attend many workshops in Turkey, to transfer the knowledge to host, and to attract the attention of promising students in Turkey.
In particular, Dr. Iskin is using all the means possible to introduce and promote his field of expertise, i.e. ultracold atomic physics, to the scientific community of the host country. Since this field is relatively new to this community, there are only a few active researchers working on it. For instance, Dr. Iskin has participated in the summer schools and workshops that are organized in ITAP (Turunc, Turkey), which are geared primarily for graduate students and postdoctoral fellows but exceptional senior undergraduates were also highly encouraged to attend. As a result of these efforts, Dr. Iskin’s research group has grown considerably in the past 4 years, currently consisting of 5 principal members (in addition to a recently graduated MS student): 1 Asst. Prof. (a former postdoc), 2 post-PhD researchers (both recruited from European institutions), and 2 PhD candidates (recruited from national universities).
In addition, as of January 2014, the Scientific and Technological Research Council of Turkey (TUBITAK) has appointed Dr. Iskin to the Turkish Physics Olympiad Team Recruitment Committee. He has already organized several training camps for the selected high schools students from all over Turkey, and attended 2014 Olympics as the team leader in Astana, Kazakhstan. Since this organization provides an excellent opportunity to expose the top science and/or engineering oriented students of Turkey to physics research in general, and as early as at the high school level, he is already committed for the 2015 Olympics and very keen on participating in this outreach program in the upcoming years to promote his research interests. Lastly, Dr. Iskin has written two popular magazine articles for the Koc University’s annual FENER and FRONTIERS magazines, both of which have a very broad audience in Turkey including most of the universities, national institutes and research centers from all around Turkey. They are also sent to R&D departments of 98 consolidated companies of the Koc corporate. Both of these articles appeared in the Fall 2012 issues, and they have allowed Dr. Iskin to introduce his expertise in cold atom physics to a much broader audience outside of academia.
1.5. Project Website: The details of the project and related material (group members, funding agencies, published and unpublished articles, etc.) can be found in the group webpage http://home.ku.edu.tr/~miskin/