In this Letter, we report the first experimental realization and investigation of a spin-orbit coupled Fermi gas. Both spin dephasing in spin dynamics and momentum distribution asymmetry of the equilibrium state are observed as hallmarks of spin-orbit coupling in a Fermi gas. The single particle dispersion is mapped out by using momentum-resolved radio-frequency spectroscopy. From momentum distribution and momentum-resolved radio-frequency spectroscopy, we observe the change of fermion population in different helicity branches consistent with a finite temperature calculation, which indicates that a Lifshitz transition of the Fermi surface topology change can be found by further cooling the system.

Spin-orbit coupling (SOC) is central to many physical phenomena, including fine structures of atomic spectra and topological phases in ultracold atoms. Whereas, in general, SOC is fixed in a system, laser-atom interaction provides a means to create and control synthetic SOC in ultracold atoms 1 . Despite significant experimental progress in this area 2-8 , two-dimensional (2D) synthetic SOC, which is crucial for exploring two-and threedimensional topological phases, is lacking. Here, we report the experimental realization of 2D SOC in ultracold 40 K Fermi gases using three lasers, each of which dresses one atomic hyperfine spin state. Through spin-injection radiofrequency (rf) spectroscopy 4 , we probe the spin-resolved energy dispersions of the dressed atoms, and observe a highly controllable Dirac point created by the 2D SOC. These results constitute a step towards the realization of new topological states of matter.There have been many theoretical proposals for creating multi-dimensional SOC in ultracold atoms 9-14 , so as to access novel macroscopic quantum phenomena and quantum topological states [15][16][17][18][19][20][21][22][23][24] . Whereas these proposals have not been realized in laboratories, physicists have also just begun to explore topological phenomena in optical lattices [25][26][27][28] . Here, we use the Raman scheme to produce a highly controllable 2D synthetic SOC for an ultracold Fermi gas of 40 K. Such SOC allows us to create and manipulate a single stable Dirac point on a 2D plane, which is detected by spin-injection rf spectroscopy 4 .We apply three far-detuned lasers propagating on the x-y plane to couple three ground hyperfine spin states, within the 4 2 S 1/2 ground electronic manifold, |1 = |F = 9/2, m F = 3/2 , |2 = |F = 9/2, m F = 1/2 and |3 = |F = 7/2, m F = 1/2 , where (F, m F ) are the quantum numbers for hyperfine spin states as shown in Fig. 1a, to the electronically excited states. Unlike the tripod scheme, where a single excited state is considered [9][10][11][15][16][17][18] , in the 40 K used here the excited states include a fine-structure doublet 4 2 P 1/2 (D 1 line) and 4 2 P 3/2 (D 2 line) with a finestructure splitting of ∼3.4 nm. Each of two D-line components also has hyperfine structures. After adiabatically eliminating excited states, the ring scheme proposed in ref. 12 is realized for three cyclically coupled states, with a generalization to arbitrary laser configurations. The Hamiltonian is written as( 1) where p denotes the momentum of atoms, k i (|k i | = 2π/λ i ) and ω i are the wavevectors and frequencies of the three lasers, Ω i are the Rabi frequencies, i, j are the indices for the three ground hyperfine spin and the excited states respectively, ε i and E j are the ground and excited state energies, n is the total number of the excited states and M ij is the matrix element of the dipole transition. Different from refs 9,10,15, each hyperfine ground spin state here is dressed by only one laser field, regardless of the excited states it is coupled to. A gau...

Gliomas are the most common type of primary brain tumor in the central nervous system of adults. Maternally Expressed Gene 3 (MEG3) is an imprinted gene located at 14q32 that encodes a non-coding RNA (ncRNA) associated with tumorigenesis. However, little is known about whether and how MEG3 regulates glioma development. In the present study we assayed the expression of MEG3 in glioma tissue samples by real-time polymerase chain reaction assay, and defined the biological functions and target genes by CCK-8 assay, flow cytometry, and RNA immunoprecipitation. We first demonstrated that MEG3 expression was markedly decreased in glioma tissues compared with adjacent normal tissues. Moreover, ectopic expression of MEG3 inhibited cell proliferation and promoted cell apoptosis in U251 and U87 MG human glioma cell lines. We further verified that MEG3 was associated with p53 and that this association was required for p53 activation. These data suggest an important role of MEG3 in the molecular etiology of glioma and implicate the potential application of MEG3 in glioma therapy.

The recent experimental realization of synthetic spin-orbit coupling (SOC) opens a new avenue for exploring novel quantum states with ultracold atoms. However, in experiments for generating twodimensional SOC (e.g., Rashba type), a perpendicular Zeeman field, which opens a band gap at the Dirac point and induces many topological phenomena, is still lacking. Here we theoretically propose and experimentally realize a simple scheme for generating two-dimension SOC and a perpendicular Zeeman field simultaneously in ultracold Fermi gases by tuning the polarization of three Raman lasers that couple three hyperfine ground states of atoms. The resulting band gap opening at the Dirac point is probed using spin injection radio-frequency spectroscopy. Our observation may pave the way for exploring topological transport and topological superfluids with exotic Majorana and Weyl fermion excitations in ultracold atoms. Spin-orbit coupling (SOC), the intrinsic interaction between a particle spin and its motion, plays a key role in many important phenomena, ranging from anomalous Hall effects [1] to topological insulators and superconductors [2][3][4]. Although SOC is ubiquitous in nature, the experimental control and observation of SOC induced effects are quite difficult. In this context, the recent experimental realization of synthetic SOC for cold atoms [5][6][7][8][9][10][11][12] provides a completely new and tunable platform for exploring SOC related physics. Early experiments only realized the 1D SOC (i.e., an equal sum of Rashba and Dresselhaus coupling, ∝ k x σ y ) using two counterpropagating Raman lasers [5][6][7][8][9][10][11][12]. Many theoretical proposals have explored the generation of 2D SOC (i.e., ∝ αk x σ y + βk y σ x ) [13][14][15][16][17][18][19][20] as well as their interesting physical properties in Bose and Fermi gases [21][22][23][24][25][26]. Recently, 2D SOC was also experimentally realized in ultracold 40 K Fermi gases [27] using three Raman lasers and the associated stable Dirac point on a 2D momentum plane was observed [27].The experimental generation of SOC is usually accompanied with a Zeeman field, which breaks various symmetries of the underlying system and induces interesting quantum phenomena. The accompanied Zeeman field can be in-plane (e.g., V σ y for SOC ∝ k x σ y ) or perpendicular (e.g., V σ z for SOC ∝ αk x σ y + βk y σ x ). The in-plane Zeeman field, while preserves the Dirac point, makes the band dispersion asymmetric, leading to new quantum states such as Fulde-Ferrell superfluids [28][29][30][31]. In contrast, the perpendicular Zeeman field can open a topological band gap at the Dirac point of the SOC, leading to many interesting topological transport [1] and superfluid phenomena, such as the long-sought Majorana [32,33] and Weyl [24,34,35] fermions. In cold atom experiments, although both in-plane and perpendicular Zeeman fields have been realized with 1D SOC, only inplane Zeeman field was realized with 2D SOC [27]. A perpendicular Zeeman field with 2D SOC is still lacked but highly...

No abstract