We thank Ji Liu and Wen Xu for involving in the experimental setup. Le Luo is a member of the Indiana University Center for Spacetime Symmetries (IUCSS). This work was supported by IUPUI and IUCRG.

NOTE: This protocol requires a home-built ultracold atom apparatus including the following equipment: two external cavity diode lasers (ECDL), a locking setup for the ECDL offset frequency locking10, a fiber laser for the ODT, an AOM for laser intensity modulation, an radio frequency (rf) antenna system with a source generator and a power amplifier, an absorption imaging system with a CCD camera, a computer program for timing sequence and data acquisition (DAQ), a computer program for imaging processing and data analysis, a pair of electromagnets for the MOT and bias magnetic fields, and an ultrahigh vacuum chamber including a 6Li vapor oven and a Zeeman slower (shown in Figure 1).
Caution: Three lasers of different powers and wavelengths are used. Please consult the relevant laser safety data sheets and choose the proper laser safety goggles.
1. Timing Control
NOTE: All timing sequences are controlled by a 128 channel PCI DAQ card through a timing control program. The resolution of the timing sequence is 100 &#181;s. Several instrumentation control programs are used to control the settings of the instruments, such as fiber laser arbitrary function generator (AFG), ODT AFG, arbitrary pulse generator (APG), parametric modulation AFG, MOT multiplexer, rf generator, etc.
<ol>
	<li>Open the timing control program and the control programs for the instruments. 
	NOTE: The timing control program sends TTL (Transistor-transistor logic) signals to the control terminals for running the timing control files. Some instruments are connected to the computer by GPIB (IEEE 488) for real-time control.</li>
	<li>Write the experiment timing file and set the timing parameters as listed in Table 1. 
	NOTE: The after MOT timing sequence is also illustrated by Figure 2.</li>
</ol>
2. CCD Camera Preparation
NOTE: CCD camera is used to record the absorption imaging of the cold atoms, which is the main diagnostic tool of cold atoms.
<ol>
	<li>Turn on the CCD camera driver and its control program. Set the CCD camera to Particle image velocimetry (PIV) mode11. Set the CCD exposure time to 5 ms. 
	NOTE: PIV mode reduces the time gap between the signal and reference frame, which increases the signal-to-noise ratio of the absorption imaging.</li>
	<li>Use an external trigger to control the CCD exposure 
	NOTE: The CCD trigger time is listed in Table 1.</li>
</ol>
3. 671 nm Laser Preparation
NOTE: A 671 nm single frequency ECDL with 500 mW output power is used to generate the MOT cooling and trapping beams. Another 671 nm ECDL of 35 mW is used for absorption imaging. A digital laser current modulation method (DLCM) is applied for laser frequency stabilization10. The related 6Li energy levels are shown in Figure 3a. Room temperature stability of 20 &#177; 1 &#176;C is required for the optimal stability of laser frequency locking.
<ol>
	<li>MOT Laser Preparation 
	NOTE: The optical setup and relevant results of the DLCM method is presented in Reference 10.
	<ol>
		<li>Turn on the 6Li atomic vapor cell heater and warm it up to 340 &#176;C.</li>
		<li>Warm up the laser locking AOM for 1 h.</li>
		<li>Turn on the laser frequency lock controller and open its software. Turn on the laser grating and current modulation of the ECDL in the software. 
		NOTE: The modulation frequency and amplitude of the grating modulation are set to 5 Hz and 1.0 V respectively. The modulation frequency and amplitude of the current modulation are set to 100 kHz and 0.0015 Vpp respectively to reduce the laser linewidth10.</li>
		<li>Turn on the ECDL emission. 
		NOTE: The laser light passes through the MOT optical setup and reaches the experiment vacuum chamber.</li>
		<li>Slightly adjust the current of the ECDL laser manually to tune the laser frequency until the lock-in error signal of the 6Li D2 line is observed, as shown in Figure 3b.</li>
		<li>Set the lock point in the control software to the 22S1/2 (F = 3/2) &#8594; 22P3/2 transition (see Figures 3a, 3b). Then lock the laser frequency to this transition, and adjust the lock point to the center of the transition10. 
		NOTE: Once the laser frequency is locked, the lock-in error signal shows a small fluctuation at the lock point corresponding to the frequency fluctuation around the lock point.</li>
	</ol>
	</li>
	<li>Imaging Laser Preparation 
	NOTE: The optical setup and relevant results of the offset locking method are presented in Reference 10.
	<ol>
		<li>Turn on the offset locking rf signal generator.</li>
		<li>Turn on the modulation of the grating, and increase the modulation amplitude to 2 V.</li>
		<li>Repeat the frequency tuning process in 3.1.4.-3.1.5. to get the laser frequency beating error signal in the oscilloscope and the rf spectrum analyzer.</li>
		<li>Lock the laser frequency to the beating signal of the offset locking through two PID feedback modules. 
		NOTE: Once the laser frequency is locked, the spectrum of the beating signal in the rf spectrum will stop at the locking point.</li>
	</ol>
	</li>
</ol>
4. Absorption Imaging Preparation
NOTE: The atoms are probed with absorption imaging, which needs two image frames. The first one with the atoms is the signal frame, and the second one without atoms is the reference frame.
<ol>
	<li>Turn on an APG and the imaging beam AOM.</li>
	<li>Set the imaging pulse duration to 10 &#181;s, and set the separation time between the two imaging frames to 5.5 ms.</li>
	<li>Set the imaging beam intensity to about 0.3Isat, where Isat = 2.54 mW/cm2 is the saturated absorption intensity of the 6Li D2 line.</li>
</ol>
5. Cooling Atoms with MOT
NOTE: MOT is a widely-used cooling method in ultracold atoms experiments. This section generates a MOT of around one billion 6Li atoms at about 300 &#181;K.
<ol>
	<li>Slow Atom Source
	<ol>
		<li>Turn on the oven heaters.</li>
		<li>After the oven temperatures reach the operational region (refer to Table 2), turn on the cooling fans for the Zeeman slower. Then slowly increase the current of the slower to 9.2 A. Turn on the current of the two crossover coils to 7 A and 1 A respectively. 
		NOTE: The temperature distribution of the oven listed in Table 2 is optimized for collimation and lifetime of the atomic source12. The location of the heaters on the oven is shown in Figure 4.</li>
		<li>Unblock the Zeeman slower laser beam manually by opening the atomic shutter. Set the frequency of the laser beam to 192 MHz red-detuned with the 22S1/2 (F = 3/2) &#8594; 22P3/2 transition. 
		NOTE: With this setup, the speed of the atoms is slowed down from 1,400 m/s to 100 m/s. The Zeeman slower is shown in Figure 5.</li>
	</ol>
	</li>
	<li>Magnetic Field Gradient 
	NOTE: This apparatus uses a pair of coils controlled by an H-bridge switch circuit to produce either an anti-Helmholtz or Helmholtz magnetic field. The coils are water cooled to prevent overheating.
	<ol>
		<li>Slowly turn on the water flow to 6 gal/min.</li>
		<li>Set the H-bridge for anti-Helmholtz magnetic field configuration by running the timing control program with the MOT loading timing file.</li>
		<li>Turn on the magnets&#39; power supplies, and set the current of each coil to about 18 A via its control program, which creates a magnetic field gradient of about 22 G/cm for the MOT. 
		NOTE: A static MOT is observed in the experiment chamber after the magnetic field gradient is turned on.</li>
	</ol>
	</li>
	<li>Dynamic MOT 
	NOTE: The optical setup of the 6Li MOT contains three pairs of counter propagating MOT beams with all pairs orthogonal to each other. Each MOT beam includes a cooling beam and a repumping beam. The intensities and frequency detunings of the beams, which are controlled by AOMs, are varied for the three phases. The control voltages of the AOMs are set via multiplexer circuits commanded by a timing control system. The parameters for three phases are listed in Table 3. The optical layout of the MOT beams is shown in Figure 6.
	<ol>
		<li>Load, compile and run the experiment timing file in the timing control program on a loop with the software control. The experiment timing starts with the MOT loading phase. Monitor the MOT fluorescence signal in the photodetector to reach 2 V, which indicates around 109 atoms in the MOT. 
		NOTE: The fluorescence of the MOT is collected by a lens with spatial angle of about 10-4 rad. The loading phase atom number can be calculated by the method in Reference 13.</li>
		<li>Use the optical shutter to block the slowing beam before the loading phase ends. 
		NOTE: The timing of the slowing beam shutter is also under control of the experiment timing, which is listed in Table 1.</li>
		<li>Set intensities and frequency detunings of the MOT laser beams according to Table 3 for the cooling phase. 
		NOTE: After the cooling phase, the temperature of the MOT is reduced to about 300 &#181;K.</li>
		<li>For the pumping phase, program the experiment timing file to turn off the repumping beams with the AOM. 
		NOTE: The pumping phase pumps all the atoms into the lowest hyperfine states 22S1/2 (F = 1/2).</li>
		<li>Turn off the MOT beams and shift the laser frequency 30 MHz below the atomic transition resonance by AOM, and block the leaking light from the AOMs with optical shutters. 
		NOTE: After the MOT stage, any leakage of the resonant light to the atomic cloud will result in atom loss. The timing of the AOM control and MOT beam shutter are all listed in Table 1.</li>
		<li>After the dynamic MOT, acquire the imaging frames from the camera. Get the absorption imaging of the MOT. 
		NOTE: The atomic number of the MOT is about 107 after the pumping phase. A typical absorption image of the MOT is shown in Figure 7a.</li>
	</ol>
	</li>
</ol>
6. Preparing an Ultracold Fermi Gas with ODT
<ol>
	<li>Optical Dipole Trap 
	NOTE: ODT is the main tool to generate ultracold Fermi gases. In order to generate a deep ODT, a fiber laser with 100 W emission power at 1064 nm wavelength is used. The setup of ODT is shown in Figure 8.
	<ol>
		<li>Turn on the water flow for cooling the laser beam dumps.</li>
		<li>Set the ODT AOM control voltage to 1 V manually. Turn on the fiber laser with 13 W emission power.</li>
		<li>Check the ODT optics with an infrared light viewer, and remove any dust with argon gas flow. 
		NOTE: Dust on the optics can change the spatial profile of the ODT, and cause instability of the ODT.</li>
		<li>Command the fiber laser AFG to generate a laser pulse via the AFG control program. 
		NOTE: The output of the laser pulse is triggered by the experiment timing, and the starting time of this pulse is set to 14 ms before the end of the MOT loading phase. The pulse sequence control is shown in Figure 1, and the timing is listed in Table 1.</li>
		<li>Manually set the ODT AOM control voltage to 8 V (80% of the saturated rf power). 
		NOTE: The maximum rf power of the AOM driver should be limited to 80% of the saturated power to reduce the thermal lensing effect.</li>
		<li>Acquire the absorption images of the MOT and ODT from the camera. 
		NOTE: Check the overlap of the MOT and ODT through their absorption imaging. Figure 7b shows typical absorption images of the MOT and ODT, respectively.</li>
	</ol>
	</li>
	<li>Bias Magnetic Field and Spin Mixing rf Field 
	NOTE: In order to generate an interacting Fermi gas, a bias magnetic field in the vertical direction is applied to tune the s-wave scattering length.
	<ol>
		<li>Set the H-bridge in the experiment timing program so that the magnetic field configuration changes from anti-Helmholtz to Helmholtz. 
		NOTE: The Helmholtz coils generate the bias magnetic field for tuning interatomic interaction.</li>
		<li>Set the bias magnetic field to 330 G in channel 2 and 527.3 G in channel 3 of the magnets control program.</li>
		<li>Program the experiment timing sequence to sweep the magnetic field from 0 G to 330 G after the MOT is turned off. 
		NOTE: This magnetic field sweep prepares a weakly interacting 6Li Fermi gas for standard evaporative cooling.</li>
		<li>Program a magnetic field sweep from 330 G to 527 G for a noninteracting Fermi gas14. 
		NOTE: The magnetic field sequence from 6.2.1-6.2.4. is shown in Figure 1, and the timing is listed in Table 1.</li>
		<li>Apply a noisy rf pulse to create a 50:50 mixture of the two lowest hyperfine states 22S1/2(F = 1/2, mF= &#177;1/2) of 6Li.</li>
		<li>Tune the locked laser frequency resonant with the atoms at 527.3 G (corresponding to the transition 22S1/2 (F = 1/2, mF = -1/2)&#160;&#8594; 22P3/2 at the low magnetic field) by changing the output frequency of the rf signal generator. 
		NOTE: The resonant frequency maximizes the atom number of the absorption imaging, which is used to guide the frequency adjustment. Only the spin-down atoms are imaged to present the atomic cloud because the 50:50 spin mixtures are used for the experiment.</li>
	</ol>
	</li>
	<li>Evaporative Cooling by Trap Lowering 
	NOTE: A standard evaporative cooling is used to cool the fermionic atoms of 6Li near the degenerate regime. The first stage of evaporative cooling is controlled by the pulse of the fiber laser and the second is controlled by the ODT AOM. The near-degenerate Fermi gas will be used as the sample for parametric cooling.
	<ol>
		<li>Start the first stage of evaporative cooling with the control software by pulsing the fiber laser power, which increases the trap depth of the ODT to U0, then back to 0.1U0 (U0 is the full trap depth with the laser power of 100 W). The total time of this stage is 0.5 s. 
		NOTE: The pulse duration corresponding to U0 should be limited to 0.5 s to avoid the thermal lensing effect.</li>
		<li>Program the ODT AOM with an exponential curve as shown in Figure 1. After the first stage of evaporative cooling is finished, wait 30 ms, and then start the second stage of evaporative cooling by lowering the trap depth from 0.1U0 to 0.01U0 through the ODT AOM. The total time of this stage is 1.5 s.</li>
		<li>Acquire the absorption imaging of the cold atoms after the evaporative cooling. 
		NOTE: About 105 atoms are left in the ODT after evaporative cooling, which can be calculated from the absorption image.</li>
	</ol>
	</li>
</ol>
7. Parametric Cooling
<ol>
	<li>Trap Depth Modulation
	<ol>
		<li>Wait 100 ms after the magnetic sweep to 527.3 G. Modulate the trap depth with the ODT AOM by U(tm) = 0.01U0(1+&#948;cos(&#969;m tm)), where &#948; is the modulation depth and &#969;m is the modulation frequency. Set the modulation time tm in the parametric modulation AFG control program. The time sequence of the modulation is shown in Figure 1. 
		NOTE: This is the key step of implementing parametric cooling.</li>
		<li>Program the APG to release the atoms from the ODT by abruptly turning off the trapping beams. Let the gas ballistically expand for 300 &#181;s before applying absorption imaging. 
		NOTE: The ballistic expansion is used with TOF absorption imaging to get the temperature of the cold atoms.</li>
		<li>Acquire the absorption image of the cold atoms after parametric cooling.</li>
	</ol>
	</li>
	<li>Time Dependence Measurement 
	NOTE: In our previous work7, we found the optimized frequency of the parametric cooling to be 1.45&#969;x, where &#969;x is the radial trapping frequency of ODT at 0.01U0. Using this frequency, we can selectively remove high-energy atoms along the axial direction.
	<ol>
		<li>Set the modulation depth to &#948; = 0.5 via the parametric modulation AFG control program.</li>
		<li>Use the external trigger control function of the parametric modulation AFG to change the modulation time from 0 to 600 ms by varying the modulation cycle numbers. 
		NOTE: With the increasing of modulation time, the size of the atomic cloud will be reduced, especially the axial direction. The relevant results are shown in Figure 9.</li>
		<li>Acquire the imaging frames from the camera. Save and analyze the images through the CCD control program.</li>
	</ol>
	</li>
</ol>

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The authors have nothing to disclose. Specific product and company citations are for the purpose of clarification only and are not an endorsement by the authors.

We present an experimental protocol for parametric cooling of a noninteracting Fermi gas in a crossed-beam optical trap. The critical steps of this protocol include: First, the optically-trapped Fermi gas needs to be cooled close to the degenerate temperature by lowering the trap depth. Second, a modulation frequency is chosen that is resonant with the anharmonic component of the trapping potential. Third, the intensity of the trapping beam is modulated to cool the atomic cloud and measure the dependence of the cloud ene...

In the past two decades, various cooling techniques have been developed for generating Bose-Einstein condensates (BEC) and degenerate Fermi gases (DFG) from hot atomic vapors1,2,3,4,5. BEC and DFG are novel phases of matter that exist in extremely low temperatures, usually one millionth of a degree above absolute zero temperature, far below those normally found on Earth or in space. To obtain such low temperatures, most cooling methods rely on lowering the trapping potential to evaporatively cool the atoms. However, the lowering scheme also decreases the collision rate of the atoms, which limits the cooling efficiency when the gas reaches the quantum regime6. In this article, we present an &#34;expelling&#34; method to evaporatively cool an ultracold Fermi gas in an ODT without lowering the trap depth. This method is based on our recent study of parametric cooling7, showing several advantages compared to the lowering schemes7,8,9.
The key idea of the parametric scheme is to employ the anharmonicity of the crossed-beam ODT, which makes the hotter atoms near the edge of the trapping potential feel the lower trapping frequencies than the colder atoms in the center. This anharmonicity allows the hotter atoms to be selectively expelled from the trap when modulating the trapping potential at frequencies resonant with the high-energy atoms.
The experimental protocol of parametric cooling requires a pre-cooled noninteracting Fermi gas near the degenerate temperature. To implement this protocol, an acousto-optic modulator (AOM) is used to modulate the intensity of the trapping beams by controlling the modulation frequency, depth and time. To verify the cooling effect, the atomic cloud is probed by absorption imaging of time-of-flight (TOF), where a resonant laser beam illuminates the atomic cloud and the absorption shadow is captured by a charge coupled device (CCD) camera. The cloud properties, such as the atom number, energy, and temperature, are determined by the column density. To characterize the cooling effect, we measure the dependence of the cloud energies on the various modulation times.

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	<tbody>
		<tr>
			<td>500 mW 671 nm ECDL</td>
			<td>Toptica</td>
			<td>TA Pro</td>
			<td>Quantity:1</td>
		</tr>
		<tr>
			<td>35 mW 671 nm ECDL</td>
			<td>Toptica</td>
			<td>DL-100</td>
			<td>Quantity:1</td>
		</tr>
		<tr>
			<td>671 nm AOM</td>
			<td>Isomet</td>
			<td>1206C</td>
			<td>Quantity:3</td>
		</tr>
		<tr>
			<td>671 nm AOM Driver</td>
			<td>Isomet</td>
			<td>630C-110</td>
			<td>Quantity:3</td>
		</tr>
		<tr>
			<td>100 W 1064 nm CW laser</td>
			<td>IPG photonics</td>
			<td>YLR-100-1064-LP</td>
			<td>Quantity:1</td>
		</tr>
		<tr>
			<td>1064 nm AOM</td>
			<td>IntraAction</td>
			<td>ATM-804DA6B&#160;</td>
			<td>Quantity:1</td>
		</tr>
		<tr>
			<td>1064 nm AOM Driver</td>
			<td>IntraAction</td>
			<td>ME-805EH&#160;</td>
			<td>Quantity:1</td>
		</tr>
		<tr>
			<td>Arbitrary Function Generator</td>
			<td>Agilent&#160;</td>
			<td>33120A</td>
			<td>Quantity:3</td>
		</tr>
		<tr>
			<td>Digital I/O Board</td>
			<td>United Electronic Industries</td>
			<td>PD2-DIO-128</td>
			<td>Quantity:1</td>
		</tr>
		<tr>
			<td>System Design Platform</td>
			<td>National Instruments</td>
			<td>LabVIEW</td>
			<td>Quantity:1</td>
		</tr>
		<tr>
			<td>Analog Voltage Output Device</td>
			<td>Measurement Computing</td>
			<td>USB-3104</td>
			<td>Quantity:1</td>
		</tr>
		<tr>
			<td>CCD Camera</td>
			<td>Hamamatsu</td>
			<td>Orca R2</td>
			<td>Quantity:1</td>
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		<tr>
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			<td>Quantity: depends on apparatus design</td>
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			<td>Quantity: depends on apparatus design</td>
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			<td>Quantity: 2, one for each ECDL</td>
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			<td>Photodetector</td>
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			<td>ADG408</td>
			<td>Quantity: 2</td>
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			<td>1064 nm plano-concave lens</td>
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			<td></td>
			<td></td>
			<td>Quantity: depends on apparatus design</td>
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			<td>1064 nm Lenses</td>
			<td></td>
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			<td>Quantity: depends on apparatus design</td>
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			<td>1064 nm Thin Film Polarizer</td>
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			<td>100 W, 1064 nm Beam Dump</td>
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			<td>100 W, 1064 nm Power Meter</td>
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			<td>Quantity:1</td>
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			<td>RF Function Generator</td>
			<td>Rigol</td>
			<td>DG4162</td>
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			<td>RF Power Amplifier</td>
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</table>

cooling an optically trapped ultracold fermi gas by periodical driving

We present a cooling method for a cold Fermi gas by parametrically driving atomic motions in a crossed-beam optical dipole trap (ODT). Our method employs the anharmonicity of the ODT, in which the hotter atoms at the edge of the trap feel the anharmonic components of the trapping potential, while the colder atoms in the center of the trap feel the harmonic one. By modulating the trap depth with frequencies that are resonant with the anharmonic components, we selectively excite the hotter atoms out of the trap while keeping the colder atoms in the trap, generating parametric cooling. This experimental protocol starts with a magneto-optical trap (MOT) that is loaded by a Zeeman slower. The precooled atoms in the MOT are then transferred to an ODT, and a bias magnetic field is applied to create an interacting Fermi gas. We then lower the trapping potential to prepare a cold Fermi gas near the degenerate temperature. After that, we sweep the magnetic field to the noninteracting regime of the Fermi gas, in which the parametric cooling can be manifested by modulating the intensity of the optical trapping beams. We find that the parametric cooling effect strongly depends on the modulation frequencies and amplitudes. With the optimized frequency and amplitude, we measure the dependence of the cloud energy on the modulation time. We observe that the cloud energy is changed in an anisotropic way, where the energy of the axial direction is significantly reduced by parametric driving. The cooling effect is limited to the axial direction because the dominant anharmonicity of the crossed-beam ODT is along the axial direction. Finally, we propose to extend this protocol for the trapping potentials of large anharmonicity in all directions, which provides a promising scheme for cooling quantum gases using external driving.

Using this protocol, we study the dependence of the parametric cooling on the modulation time with the optimized modulation frequency and amplitude, both of which have been determined in our previous publication7. We first prepare a noninteracting Fermi gas of 6Li atoms in the two lowest hyperfine states with a temperature of T/TF &#8776; 1.2. Here, TF = (6N)1/3&#295;&#969;/<em...

Watch this Scientific Journal Video about Cooling an Optically Trapped Ultracold Fermi Gas by Periodical Driving at JoVE.com

Cooling an Optically Trapped Ultracold Fermi Gas by Periodical Driving

We present a parametric driving method to cool an ultracold Fermi gas in a crossed-beam optical dipole trap. This method selectively removes high-energy atoms from the trap by periodically modulating the trap depth with frequencies that are resonant with the anharmonic components of the trapping potential.

We present a cooling method for a cold Fermi gas by parametrically driving atomic motions in a crossed-beam optical dipole trap (ODT). Our method employs ...

cooling-an-optically-trapped-ultracold-fermi-gas-by-periodical-driving

Research

JoVE Journal

Engineering

7.4K Views.  Indiana University–Purdue University Indianapolis (IUPUI). We present a parametric driving method to cool an ultracold Fermi gas in a crossed-beam optical dipole trap. This method selectively removes high-energy atoms from the trap by periodically modulating the trap depth with frequencies that are resonant with the anharmonic components of the trapping potential. 

Video: Cooling an Optically Trapped Ultracold Fermi Gas by Periodical Driving

Investigating Single Molecule Adhesion by Atomic Force Spectroscopy

Atomic force spectroscopy is an ideal tool to study molecules at surfaces and interfaces. An experimental protocol to couple a large variety of single molecules covalently onto an AFM tip is presented. At the same time the AFM tip is passivated to prevent unspecific interactions between the tip and the substrate, which is a prerequisite to study single molecules attached to the AFM tip. Analyses to determine the adhesion force, the adhesion length, and the free energy of these molecules on solid surfaces and bio-interfaces are shortly presented and external references for further reading are provided. Example molecules are the poly(amino acid) polytyrosine, the graft polymer PI-g-PS and the phospholipid POPE (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine). These molecules are desorbed from different surfaces like CH3-SAMs, hydrogen terminated diamond and supported lipid bilayers under various solvent conditions. Finally, the advantages of force spectroscopic single molecule experiments are discussed including means to decide if truly a single molecule has been studied in the experiment.

A protocol to couple a large variety of single molecules covalently onto an AFM tip is presented. Procedures and examples to determine the adhesion force and free energy of these molecules on solid supports and bio-interfaces are provided.

Atomic force spectroscopy is an ideal tool to study molecules at surfaces and interfaces. An experimental protocol to couple a large variety of single ...

Experimental Methods for Investigation of Shape Memory Based Elastocaloric Cooling Processes and Model Validation

Shape Memory Alloys (SMA) using elastocaloric cooling processes have the potential to be an environmentally friendly alternative to the conventional vapor compression based cooling process. Nickel-Titanium (Ni-Ti) based alloy systems, especially, show large elastocaloric effects. Furthermore, exhibit large latent heats which is a necessary material property for the development of an efficient solid-state based cooling process. A scientific test rig has been designed to investigate these processes and the elastocaloric effects in SMAs. The realized test rig enables independent control of an SMA&#39;s mechanical loading and unloading cycles, as well as conductive heat transfer between SMA cooling elements and a heat source/sink. The test rig is equipped with a comprehensive monitoring system capable of synchronized measurements of mechanical and thermal parameters. In addition to determining the process-dependent mechanical work, the system also enables measurement of thermal caloric aspects of the elastocaloric cooling effect through use of a high-performance infrared camera. This combination is of particular interest, because it allows illustrations of localization and rate effects &#8212; both important for efficient heat transfer from the medium to be cooled.
The work presented describes an experimental method to identify elastocaloric material properties in different materials and sample geometries. Furthermore, the test rig is used to investigate different cooling process variations. The introduced analysis methods enable a differentiated consideration of material, process and related boundary condition influences on the process efficiency. The comparison of the experimental data with the simulation results (of a thermomechanically coupled finite element model) allows for better understanding of the underlying physics of the elastocaloric effect. In addition, the experimental results, as well as the findings based on the simulation results, are used to improve the material properties.

Experimental methods for investigation of solid state cooling processes and characterization of elastocaloric material properties of Shape Memory Alloys (SMA) are presented. A custom-built test rig has been designed for controlling and comprehensive monitoring of elastocaloric cooling processes. Furthermore, it provides a validation platform for thermomechanically coupled modeling approaches.

Shape Memory Alloys (SMA) using elastocaloric cooling processes have the potential to be an environmentally friendly alternative to the conventional vapor ...

Stimulated Stokes and Antistokes Raman Scattering in Microspherical Whispering Gallery Mode Resonators

Dielectric microspheres can confine light and sound for a length of time through high quality factor whispering gallery modes (WGM). Glass microspheres can be thought as a store of energy with a huge variety of applications: compact laser sources, highly sensitive biochemical sensors and nonlinear phenomena. A protocol for the fabrication of both the microspheres and coupling system is given. The couplers described here are tapered fibers. Efficient generation of nonlinear phenomena related to third order optical non-linear susceptibility &#935;(3) interactions in triply resonant silica microspheres is presented in this paper. The interactions here reported are: Stimulated Raman Scattering (SRS), and four wave mixing processes comprising Stimulated Anti-stokes Raman Scattering (SARS). A proof of the cavity-enhanced phenomenon is given by the lack of correlation among the pump, signal and idler: a resonant mode has to exist in order to obtain the pair of signal and idler. In the case of hyperparametric oscillations (four wave mixing and stimulated anti-stokes Raman scattering), the modes must fulfill the energy and momentum conservation and, last but not least, have a good spatial overlap.

Efficient generation of nonlinear phenomena related to third order optical non-linear susceptibility &#935;(3) interactions in triply resonant silica microspheres is presented in this paper. The interactions here reported are: Stimulated Raman Scattering (SRS), and four wave mixing processes comprising Stimulated Anti-stokes Raman Scattering (SARS).

Dielectric microspheres can confine light and sound for a length of time through high quality factor whispering gallery modes (WGM). Glass microspheres ...

Adsorption Device Based on a Langatate Crystal Microbalance for High Temperature High Pressure Gas Adsorption in Zeolite H-ZSM-5

We present a high-temperature and high-pressure gas adsorption measurement device based on a high-frequency oscillating microbalance (5 MHz langatate crystal microbalance, LCM) and its use for gas adsorption measurements in zeolite H-ZSM-5. Prior to the adsorption measurements, zeolite H-ZSM-5 crystals were synthesized on the gold electrode in the center of the LCM, without covering the connection points of the gold electrodes to the oscillator, by the steam-assisted crystallization (SAC) method, so that the zeolite crystals remain attached to the oscillating microbalance while keeping good electroconductivity of the LCM during the adsorption measurements. Compared to a conventional quartz crystal microbalance (QCM) which is limited to temperatures below 80 &#176;C, the LCM can realize the adsorption measurements in principle at temperatures as high as 200-300 &#176;C (i.e., at or close to the reaction temperature of the target application of one-stage DME synthesis from the synthesis gas), owing to the absence of crystalline-phase transitions up to its melting point (1,470 &#176;C). The system was applied to investigate the adsorption of CO2, H2O, methanol and dimethyl ether (DME), each in the gas phase, on zeolite H-ZSM-5 in the temperature and pressure range of 50-150 &#176;C and 0-18 bar, respectively. The results showed that the adsorption isotherms of these gases in H-ZSM-5 can be well fitted by Langmuir-type adsorption isotherms. Furthermore, the determined adsorption parameters, i.e., adsorption capacities, adsorption enthalpies, and adsorption entropies, compare well to literature data. In this work, the results for CO2 are shown as an example.

A protocol for high-temperature and high-pressure gas adsorption measurements on zeolite H-ZSM-5 using an adsorption measurement device based on a langatate crystal microbalance is presented. Prior to the adsorption measurements, the synthesis of zeolite H-ZSM-5 on the langatate crystal microbalance sensor by the steam-assisted crystallization (SAC) method is demonstrated.

We present a high-temperature and high-pressure gas adsorption measurement device based on a high-frequency oscillating microbalance (5 MHz langatate ...

Quantitative Hardness Measurement by Instrumented AFM-indentation

In this work, a combination of amplitude-modulated non-contact atomic force microscopy and atomic force spectroscopy is applied for instrumented hardness measurements on an Au(111) surface with atomistic resolution of single plasticity events. A careful experimental procedure is described that includes the force sensor selection, its calibration, the calibration of the cantilever deflection detection system, and the minimization of instrumental drift for accurate and reproducible force-distance measurements. Also, a method for the data analysis is presented that allows the extraction of force-penetration curves from recorded force-distance curves. A typical curve displays a clear elastic deformation regime up to the first plasticity event, or pop-in, with a length in the range of one to two Burger's vectors. Later plasticity events exhibit the same magnitude. The work of plasticity is further extracted from the measurements. Finally, the hardness is determined in combination with the indentation curve using non-contact atomic force microscopy images of the remaining indents.

This experimental protocol describes how atomic force microscopy can be used to measure hardness at the true nanometer scale and to detect single atomistic plasticity events.

In this work, a combination of amplitude-modulated non-contact atomic force microscopy and atomic force spectroscopy is applied for instrumented hardness ...

Scalable Quantum Integrated Circuits on Superconducting Two-Dimensional Electron Gas Platform

To form a coherent quantum transport in hybrid superconductor-semiconductor (S-Sm) junctions, the formation of a homogeneous and barrier-free interface between two different materials is necessary. The S-Sm junction with high interface transparency will then facilitate the observation of the induced hard superconducting gap, which is the key requirement to access the topological phases (TPs) and observation of exotic quasiparticles such as Majorana zero modes (MZM) in hybrid systems. A material platform that can support observation of TPs and allows the realization of complex and branched geometries is therefore highly demanding in quantum processing and computing science and technology. Here, we introduce a two-dimensional material system and study the proximity induced superconductivity in semiconducting two-dimensional electron gas (2DEG) that is the basis of a hybrid quantum integrated circuit (QIC). The 2DEG is a 30 nm thick In0.75Ga0.25As quantum well that is buried between two In0.75Al0.25As barriers in a heterostructure. Niobium (Nb) films are used as the superconducting electrodes to form Nb- In0.75Ga0.25As -Nb Josephson junctions (JJs) that are symmetric, planar and ballistic. Two different approaches were used to form the JJs and QICs. The long junctions were fabricated photolithographically, but e-beam lithography was used for short junctions&#8217; fabrication. The coherent quantum transport measurements as a function of temperature in the presence/absence of magnetic field B are discussed. In both device fabrication approaches, the proximity induced superconducting properties were observed in the In0.75Ga0.25As 2DEG. It was found that e-beam lithographically patterned JJs of shorter lengths result in observation of induced superconducting gap at much higher temperature ranges. The results that are reproducible and clean suggesting that the hybrid 2D JJs and QICs based on In0.75Ga0.25As quantum wells could be a promising material platform to realize the real complex and scalable electronic and photonic quantum circuitry and devices.

Quantum integrated circuits (QICs) consisting of array of planar and ballistic Josephson junctions (JJs) based on In0.75Ga0.25As two-dimensional electron gas (2DEG) is demonstrated. Two different methods for fabrication of the two-dimensional (2D) JJs and QICs are discussed followed by the demonstration of quantum transport measurements in sub-Kelvin temperatures.

To form a coherent quantum transport in hybrid superconductor-semiconductor (S-Sm) junctions, the formation of a homogeneous and barrier-free interface ...

An Efficient Method for Selective Desalination of Radioactive Iodine Anions by Using Gold Nanoparticles-Embedded Membrane Filter

Here, we demonstrate a detail protocol for the preparation of nanomaterials-embedded composite membranes and its application to the efficient and ion-selective removal of radioactive iodines. By using citrate-stabilized gold nanoparticles (mean diameter: 13 nm) and cellulose acetate membranes, gold nanoparticle-embedded cellulose acetate membranes (Au-CAM) have easily been fabricated. The nano-adsorbents on Au-CAM were highly stable in the presence of high concentration of inorganic salts and organic molecules. The iodide ions in aqueous solutions could rapidly be captured by this engineered membrane. Through a filtration process using an Au-CAM containing filter unit, excellent removal efficiency (&gt;99%) as well as ion-selective desalination result was achieved in a short time. Moreover, Au-CAM provided good reusability without significant decrease of its performances. These results suggested that the present technology using the engineered hybrid membrane will be a promising process for the large-scale decontamination of radioactive iodine from liquid wastes.

An efficient method for the rapid and ion-selective desalination of radioactive iodine in several aqueous solutions is described by using gold nanoparticles-immobilized cellulose acetate membrane filters.

Here, we demonstrate a detail protocol for the preparation of nanomaterials-embedded composite membranes and its application to the efficient and ...

Infrared Degenerate Four-wave Mixing with Upconversion Detection for Quantitative Gas Sensing

We present a protocol for performing gas spectroscopy using infrared degenerated four-wave mixing (IR-DFWM), for the quantitative detection of gas species in the ppm-to-single-percent range. The main purpose of the method is the spatially resolved detection of low-concentration species, which have no transitions in the visible or near-IR spectral range that could be used for detection. IR-DFWM is a nonintrusive method, which is a great advantage in combustion research, as inserting a probe into a flame can change it drastically. The IR-DFWM is combined with upconversion detection. This detection scheme uses sum-frequency generation to move the IR-DFWM signal from the mid-IR to the near-IR region, to take advantage of the superior noise characteristics of silicon-based detectors. This process also rejects most of the thermal background radiation. The focus of the protocol presented here is on the proper alignment of the IR-DFWM optics and on how to align an intracavity upconversion detection system.

Here, we present a protocol to perform sensitive, spatially resolved gas spectroscopy in the mid-infrared region, using degenerate four-wave mixing combined with upconversion detection.

We present a protocol for performing gas spectroscopy using infrared degenerated four-wave mixing (IR-DFWM), for the quantitative detection of gas species ...

Rendering SiO2/Si Surfaces Omniphobic by Carving Gas-Entrapping Microtextures Comprising Reentrant and Doubly Reentrant Cavities or Pillars

We present microfabrication protocols for rendering intrinsically wetting materials repellent to liquids (omniphobic) by creating gas-entrapping microtextures (GEMs) on them comprising cavities and pillars with reentrant and doubly reentrant features. Specifically, we use SiO2/Si as the model system and share protocols for two-dimensional (2D) designing, photolithography, isotropic/anisotropic etching techniques, thermal oxide growth, piranha cleaning, and storage towards achieving those microtextures. Even though the conventional wisdom indicates that roughening intrinsically wetting surfaces (&#952;o &#60; 90&#176;) renders them even more wetting (&#952;r &#60; &#952;o &#60; 90&#176;), GEMs demonstrate liquid repellence despite the intrinsic wettability of the substrate. For instance, despite the intrinsic wettability of silica &#952;o &#8776; 40&#176; for the water/air system, and &#952;o &#8776; 20&#176; for the hexadecane/air system, GEMs comprising cavities entrap air robustly on immersion in those liquids, and the apparent contact angles for the droplets are &#952;r &#62; 90&#176;. The reentrant and doubly reentrant features in the GEMs stabilize the intruding liquid meniscus thereby trapping the liquid-solid-vapor system in metastable air-filled states (Cassie states) and delaying wetting transitions to the thermodynamically-stable fully-filled state (Wenzel state) by, for instance, hours to months. Similarly, SiO2/Si surfaces with arrays of reentrant and doubly reentrant micropillars demonstrate extremely high contact angles (&#952;r &#8776; 150&#176;&#8211;160&#176;) and low contact angle hysteresis for the probe liquids, thus characterized as superomniphobic. However, on immersion in the same liquids, those surfaces dramatically lose their superomniphobicity and get fully-filled within &#60;1 s. To address this challenge, we present protocols for hybrid designs that comprise arrays of doubly reentrant pillars surrounded by walls with doubly reentrant profiles. Indeed, hybrid microtextures entrap air on immersion in the probe liquids. To summarize, the protocols described here should enable the investigation of GEMs in the context of achieving omniphobicity without chemical coatings, such as perfluorocarbons, which might unlock the scope of inexpensive common materials for applications as omniphobic materials. Silica microtextures could also serve as templates for soft materials.

Rendering SiO2/Si Surfaces Omniphobic by Carving Gas-Entrapping Microtextures Comprising Reentrant and Doubly Reentrant Cavities or Pillars

This work presents microfabrication protocols for achieving cavities and pillars with reentrant and doubly reentrant profiles on SiO2/Si wafers using photolithography and dry etching. Resulting microtextured surfaces demonstrate remarkable liquid repellence, characterized by robust long-term entrapment of air under wetting liquids, despite the intrinsic wettability of silica.

We present microfabrication protocols for rendering intrinsically wetting materials repellent to liquids (omniphobic) by creating gas-entrapping ...

Proof-of-Concept for Gas-Entrapping Membranes Derived from Water-Loving SiO2/Si/SiO2 Wafers for Green Desalination

Desalination through direct contact membrane distillation (DCMD) exploits water-repellent membranes to robustly separate counterflowing streams of hot and salty seawater from cold and pure water, thus allowing only pure water vapor to pass through. To achieve this feat, commercial DCMD membranes are derived from or coated with water-repellent perfluorocarbons such as polytetrafluoroethylene (PTFE) and polyvinylidene difluoride (PVDF). However, the use of perfluorocarbons is limiting due to their high cost, non-biodegradability, and vulnerability to harsh operational conditions. Unveiled here is a new class of membranes referred to as gas-entrapping membranes (GEMs) that can robustly entrap air upon immersion in water. GEMs achieve this function by their microstructure rather than their chemical make-up. This work demonstrates a proof-of-concept for GEMs using intrinsically wetting SiO2/Si/SiO2 wafers as the model system; the contact angle of water on SiO2 is &#952;o &#8776; 40&#176;. Silica-GEMs had 300 &#956;m-long cylindrical pores whose diameters at the (2 &#956;m-long) inlet and outlet regions were significantly smaller; this geometrically discontinuous structure, with 90&#176; turns at the inlets and outlets, is known as the &#34;reentrant microtexture&#34;. The microfabrication protocol for silica-GEMs entails designing, photolithography, chrome sputtering, and isotropic and anisotropic etching. Despite the water loving nature of silica, water does not intrude silica-GEMs on submersion. In fact, they robustly entrap air underwater and keep it intact even after six weeks (&#62;106 seconds). On the other hand, silica membranes with simple cylindrical pores spontaneously imbibe water (&#60; 1 s). These findings highlight the potential of the GEMs architecture for separation processes. While the choice of SiO2/Si/SiO2 wafers for GEMs is limited to demonstrating the proof-of-concept, it is expected that the protocols and concepts presented here will advance the rational design of scalable GEMs using inexpensive common materials for desalination and beyond.

Proof-of-Concept for Gas-Entrapping Membranes Derived from Water-Loving SiO2/Si/SiO2 Wafers for Green Desalination

Presented here is a stepwise protocol for realizing gas-entrapping membranes (GEMs) from SiO2/Si wafers using integrated circuit microfabrication technology. When silica-GEMs are immersed in water, the intrusion of water is prevented, despite the water-loving composition of silica.

Desalination through direct contact membrane distillation (DCMD) exploits water-repellent membranes to robustly separate counterflowing streams of hot and ...