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Production of dual species Bose-Einstein condensates of $^{39}$K and $^{87}$Rb
Authors:
Cheng-Dong Mi,
Khan Sadiq Nawaz,
Peng-Jun Wang,
Liang-Chao Chen,
Zeng-ming Meng,
Lianghui Huang,
Jing Zhang
Abstract:
We report the production of $^{39}$K and $^{87}$Rb Bose-Einstein condensates (BECs) in the lowest hyperfine states $| F=1,m_{F}=1 \rangle$ simultaneously. We collect atoms in bright/dark magneto-optical traps (MOTs) of $^{39}$K/$^{87}$Rb to overcome the light-assisted losses of $^{39}$K atoms. Gray molasses cooling on the D1 line of the $^{39}$K is used to effectively increase the phase density, w…
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We report the production of $^{39}$K and $^{87}$Rb Bose-Einstein condensates (BECs) in the lowest hyperfine states $| F=1,m_{F}=1 \rangle$ simultaneously. We collect atoms in bright/dark magneto-optical traps (MOTs) of $^{39}$K/$^{87}$Rb to overcome the light-assisted losses of $^{39}$K atoms. Gray molasses cooling on the D1 line of the $^{39}$K is used to effectively increase the phase density, which improves the loading efficiency of $^{39}$K into the quadrupole magnetic trap. Simultaneously, the normal molasses are employed for $^{87}$Rb. After the microwave evaporation cooling on $^{87}$Rb in the optically plugged magnetic trap, the atoms mixture is transferred to a crossed optical dipole trap, where the collisional properties of the two species in different combinations of the hyperfine states are studied. The dual species BECs of $^{39}$K and $^{87}$Rb are obtained by further evaporative cooling in optical dipole trap at a magnetic field of 372.6 G with the background repulsive interspecies scattering length $a_{KRb}$ = 34 $a_{0}$ ($a_{0}$ is the Bohr radius) and the intraspecies scattering length $a_{K}$ = 20.05 $a_{0}$.
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Submitted 19 April, 2021;
originally announced April 2021.
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Photoassociation spectroscopy of weakly bound $^{87}Rb_{2}$ molecules near $5P_{1/2} +5S_{1/2}$ threshold by optical Bragg scattering in Bose-Einstein condensates
Authors:
Khan Sadiq Nawaz,
Liangchao Chen,
Chengdong Mi,
Zengming Meng,
Lianghui Huang,
Pengjun Wang,
Jing Zhang
Abstract:
We report the high resolution photoassociation (PA) spectroscopy of a $^{87}Rb$ Bose-Einstein condensate (BEC) to excited molecular states near the dissociation limit of $5P_{1/2} +5S_{1/2}$ by optical Bragg scattering. Since the detection of optical Bragg scattering in BEC has a high signal-noise ratio, we obtain the high resolution PA spectrum of excited molecular states in the range of $\pm1$ G…
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We report the high resolution photoassociation (PA) spectroscopy of a $^{87}Rb$ Bose-Einstein condensate (BEC) to excited molecular states near the dissociation limit of $5P_{1/2} +5S_{1/2}$ by optical Bragg scattering. Since the detection of optical Bragg scattering in BEC has a high signal-noise ratio, we obtain the high resolution PA spectrum of excited molecular states in the range of $\pm1$ GHz near the dissociation limit of $5P_{1/2} +5S_{1/2}$. We compare the results with the conventional method of trap loss and show that the results agree each other very well. Many interesting phenomena of excited molecular states are observed, such as light-induced frequency shift and the anomalous strong bound molecular lines at the atomic transition from $|F=1\rangle$ to $|F^{\prime}=2\rangle$. The observed excited molecular states in the range of $\pm1$ GHz near the dissociation limit of $5P_{1/2} +5S_{1/2}$ are never reported before, which will help to further improve the long range bound state models near the dissociation limit.
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Submitted 18 October, 2020;
originally announced October 2020.
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Quantum capacitance in monolayers of silicene and related buckled materials
Authors:
S. Nawaz,
M. Tahir
Abstract:
Silicene and related buckled materials are distinct from both the conventional two dimensional electron gas and the famous graphene due to strong spin orbit coupling and the buckled structure. These materials have potential to overcome limitations encountered for graphene, in particular the zero band gap and weak spin orbit coupling. We present a theoretical realization of quantum capacitance whic…
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Silicene and related buckled materials are distinct from both the conventional two dimensional electron gas and the famous graphene due to strong spin orbit coupling and the buckled structure. These materials have potential to overcome limitations encountered for graphene, in particular the zero band gap and weak spin orbit coupling. We present a theoretical realization of quantum capacitance which has advantages over the scattering problems of traditional transport measurements. We derive and discuss quantum capacitance as a function of the Fermi energy and temperature taking into account electron-hole puddles through a Gaussian broadening distribution. Our predicted results are very exciting and pave the way for future spintronic and valleytronic devices.
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Submitted 22 October, 2015;
originally announced October 2015.
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Ultra low noise YBCO nanoSQUIDs implementing nanowires
Authors:
Riccardo Arpaia,
Marco Arzeo,
Shahid Nawaz,
Sophie Charpentier,
Floriana Lombardi,
Thilo Bauch
Abstract:
We present results on ultra low noise YBa$_2$Cu$_3$O$_{7-δ}$ nano Superconducting QUantum Interference Devices (nanoSQUIDs). To realize such devices, we implemented high quality YBCO nanowires, working as weak links between two electrodes. We observe critical current modulation as a function of an externally applied magnetic field in the full temperature range below the transition temperature…
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We present results on ultra low noise YBa$_2$Cu$_3$O$_{7-δ}$ nano Superconducting QUantum Interference Devices (nanoSQUIDs). To realize such devices, we implemented high quality YBCO nanowires, working as weak links between two electrodes. We observe critical current modulation as a function of an externally applied magnetic field in the full temperature range below the transition temperature $T_C$. The white flux noise below 1 $μΦ_0/\sqrt{\mathrm{Hz}}$ at T = 8 K makes our nanoSQUIDs very attractive for the detection of small spin systems.
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Submitted 27 January, 2014;
originally announced January 2014.
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Josephson-like behavior in YBa$_2$Cu$_3$O$_{7-δ}$ nano-bridges carrying the depairing current
Authors:
Shahid Nawaz,
Riccardo Arpaia,
Floriana Lombardi,
Thilo Bauch
Abstract:
We have investigated the zero-field critical supercurrent of YBa$_2$Cu$_3$O$_{7-δ}$ bridges patterned from 50 nm thick films as a function of bridge width, ranging from 2 $μ$m to 50 nm. The critical current density monotonically increases for decreasing bridge width even for widths smaller than the Pearl length. This behavior is accounted for by considering current crowding effects at the junction…
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We have investigated the zero-field critical supercurrent of YBa$_2$Cu$_3$O$_{7-δ}$ bridges patterned from 50 nm thick films as a function of bridge width, ranging from 2 $μ$m to 50 nm. The critical current density monotonically increases for decreasing bridge width even for widths smaller than the Pearl length. This behavior is accounted for by considering current crowding effects at the junction between the bridge and the wider electrodes. Comparison to numerical calculations of the current distributions in our bridge geometries of various widths yields a (local) critical current density at 4.2 K of $1.3\times 10^8$ A/cm$^2$, the Ginzburg Landau depairing current density. The observation of up to 160 Shapiro-like steps in the current voltage characteristics under microwave irradiation substantiates the pristine character of our nano bridges with cross sections as small as $50\times 50$ nm$^2$.
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Submitted 23 January, 2013; v1 submitted 21 January, 2013;
originally announced January 2013.
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Improved nanopatterning for YBCO nanowires approaching the depairing current
Authors:
R. Arpaia,
S. Nawaz,
F. Lombardi,
T. Bauch
Abstract:
An improved nanopatterning procedure has been developed to obtain YBCO nanowires with cross sections as small as 50x50 nm^2, protected by an Au capping layer. To probe the effective role of the Au protecting layer, we have measured the current-voltage characteristics and the resistive transition in temperature of the nanowires. Critical current densities up to 10^8 A/cm^2 have been achieved at T=4…
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An improved nanopatterning procedure has been developed to obtain YBCO nanowires with cross sections as small as 50x50 nm^2, protected by an Au capping layer. To probe the effective role of the Au protecting layer, we have measured the current-voltage characteristics and the resistive transition in temperature of the nanowires. Critical current densities up to 10^8 A/cm^2 have been achieved at T=4.2 K, approaching the theoretical depairing current limit. The resistance, measured as a function of temperature close to Tc, has been fitted with a thermal activated phase slip model, including the effect of the gold layer. The extracted values of the superconducting coherence length and of the London penetration depth give current densities consistent with the measured ones. These results cannot be achieved with same nanowires, without the Au capping layer.
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Submitted 18 January, 2013;
originally announced January 2013.