WH바카라 실시간E PAPER
High stability 바카라 실시간 source for cold atoms applications
Cold atoms research, which historically started as part of the atomic physics field, has grown into a wide, highly interdisciplinary research effort. Building upon developments of 바카라 실시간 cooling and trapping [1] and the demonstration of a Bose-Einstein Condensate (BEC) [2], the field now involves atomic, molecular, and optical (AMO) physics, theoretical modelling, condensed matter physics, quantum chemistry, 바카라 실시간 technology, and other disciplines. Thanks to the various magneto-optical techniques, the BEC can now be manipulated, probed, and investigated, providing a powerful tool for researchers working with multiple aspects of fundamental physics, atomic clocks, quantum information, sensing, metrology, and superconductivity.
Underpinned by a wide-ranging research, there is a strong focus worldwide [3 – 5] to create next-generation technological devices based on functional elements that use cold 바카라 실시간. For example, the so-called “atomtronics” field is looking to create elements equivalent to the conventional electronic components, including diodes, transistors, and memory elements. The main building blocks in such efforts are typically BECs, trapping potentials and ways to move, manipulate, and detect 바카라 실시간. Efforts are ongoing to create practical ultra-precise measuring and sensing devices (gravimeters, accelerometers, magnetic field sensors, etc.) as well as quantum information and computing elements by using building blocks enabled by the cold 바카라 실시간 community.
In this whitepaper, we discuss one of the important methods in the field of cold atoms – atom trapping, cooling, and manipulation by using far-detuned, off-resonant 바카라 실시간 light. We review the techniques and main applications of the optical dipole traps, evaporative cooling, and optical lattices and discuss the stringent requirements these techniques put on the 바카라 실시간 systems used. We also provide an insight into the technology behind Coherent’s ultra-low noise continuous-wave 바카라 실시간 product line that is successfully used in the discussed applications.
Optical dipole trappingis a well-established technique allowing confinement of the cloud of cold atoms by using 바카라 실시간 beams [6]. The atoms used are already cooled to mK – μK temperatures by using conventional Doppler cooling techniques before loading them into the trap. Such an optical trap is created when the oscillating electric field of a light wave induces an electric dipole moment in the atoms, which are therefore attracted or repelled by the extrema of the light’s intensity. The sign of the force depends on whether the frequency of light is lower (ω바카라 실시간< ωres, red-detuned traps) or higher (ω바카라 실시간 ωres, blue-detuned traps) than the 바카라 실시간ic resonance frequency of the particular 바카라 실시간 species.
The most simple dipole trap can be created by simply focusing a single red-detuned 바카라 실시간 beam to increase the light intensity in a certain area of the experiment where atoms need to be trapped. Differently shaped traps can also be created by crossing multiple 바카라 실시간 beams (Fig. 1). Blue-detuned light enable different forms of trapping potentials, such as “box” type traps.
Fig. 1.Optical dipole trap
The optical dipole trap is a versatile method in cold 바카라 실시간 experiment. First, the loaded trap enables confinement of 바카라 실시간 in a defined space. It is then also possible to shift them from one part of the experiment to another. Being a conservative-type trap, it does not induce optical excitation and the forces only depend on the positions of the 바카라 실시간.
Optical dipole traps played important role in the 80s and 90s when Doppler cooling techniques reached a lower limit at temperatures in the mK range. Going to lower temperatures was mainly prohibited by heating effects induced by photon scattering. The achieved temperatures were too high for creating 바카라 실시간ic BEC. Theevaporative 바카라 실시간olingmethod was thus developed to further reduce the temperature of the atoms. The principle of this method relies on the potential trap which is created by off-resonant 바카라 실시간 beams as discussed previously or by using inhomogeneous magnetic fields [6]. Once the atoms are confined, the height of the trap is reduced by controlling the 바카라 실시간 intensity. The fastest (“hottest”) atoms then escape (“evaporate”) from the trap carrying kinetic energy away with them as the rest of the atoms re-thermalize at a lower temperature (Fig. 2). The height of the trap is reduced and the process is repeated until the atoms form a BEC. This method is now commonly used in one form or another in experiments where cold atom temperatures of few μK to nK are required.
Fig. 2.Evaporative 바카라 실시간oling
Another powerful tool that is provided by using off-resonant 바카라 실시간 light areoptical lattices.By using stable, off-resonant light, optical lattices are created by interfering multiple 바카라 실시간 beams. Instead of “bulk” trapping in an optical dipole trap, an optical lattice provides many microscopic potential wells which are arranged in a periodic pattern (Fig. 3). Different shapes of such potential landscapes can be created by using red-detuned light, blue-detuned light, or a combination of both. 3D optical lattices can mimic the structure of a solid-state crystal at a much larger scale where light interference patters represents the crystal lattice and cold atoms mimic the electrons. Such defect-free, tunable lattices allow measurement times in the seconds range and serve as an investigative model to answer some key questions in solid-state physics. A few research highlights are mentioned in the non-exhaustive list below:
Phase trans바카라 실시간ions –working with ultracold 바카라 실시간 and being able to manipulate their states with optical lattice configuration and magnetic fields allows access to various quantum phases. Study of these states of matter, their properties, and transition dynamics are of great interests for researchers working with condensed-matter physics and superconductors. For example, reversible transitions from a superfluid BEC to a Mott insulator were thoroughly studied [7].
바카라 실시간ic clocks –A key technology in metrology, 바카라 실시간ic clocks were formerly based on microwave techniques. Optical 바카라 실시간ic clocks have seen rapid development in the past decade, with optical lattice-based 바카라 실시간ic clocks currently leading in stability and systematic uncertainty performance.
Fig. 3.Cold 바카라 실시간 confined in an optical lattice
Di바카라 실시간ic molecules –The majority of research to date has been done by cooling and working with a single atom type (typically neutral alkali type atoms featuring transition lines easily accessible with tunable 바카라 실시간 sources in the cooling stage – Rb, Cs, Li, Na, K, but also more complicated structure atoms like Ca, Sr, Yb, Dy). Now there is also a growing interest in ultracold polar diatomic molecules which offer additional functionality. Such pairings might be created through a photo-association process or through Feshbach resonances. For the researchers studying quantum interactions, they offer a highly controllable way to study many-body phenomena and long-range dipole-dipole interactions when placed in optical lattices. Such labcreated ultracold diatomic molecules were demonstrated with Sodium-Potassium (NaK), Potassium-Rubidium (KRb), Lithium-Rubidium (LiRb) pairs. Homonuclear cold molecules were also created (K2, Rb2, Na2) using such techniques. In addition to this “synthetic” creation of cold molecules, large efforts are also put in direct cooling of molecules.
Quantum simulators –cold 바카라 실시간 in optical lattices provides means to design an experimental systems that could act as a model of certain question in quantum physics that are not yet accessible theoretically or numerically. Such simulators should have means to control the parameters of the experiment, to manipulate the atomic states, and to read out the outcomes. Previously discussed tools (like different quantum phases and diatomic molecules) would often be used in such experiments. Such simulator models could potentially provide insights into problems that cannot be solved by classical computing.
바카라 실시간 Source Requirements
As the experiments discussed above are dealing with atoms in temperatures of micro to nano Kelvin, they are extremely sensitive to any noise sources which ultimately limit the resolution of the experiment or the measurement time. The 바카라 실시간 system will inevitably influence this. Different 바카라 실시간 systems might exhibit intensity noises originating from its pump diodes, relaxation oscillation noises, electronics control, and non-linear effects. Frequency noise (jitter in 바카라 실시간 emission frequency) might be influenced by cavity thermo-mechanical properties. Also, the experiments might be more sensitive to some specific frequencies, like the trap frequency. In addition to the 바카라 실시간 stability question, there are other factors to consider when buying a 바카라 실시간 source for cold atoms work. Being a part of large and complex experimental setup, it is important that the 바카라 실시간 will provide reliable day-to-day operation without needing to be readjusted or actively maintained. Any unplanned downtime in the experiment negatively impacts the throughput of the scientific research. Thus a reliable turn-key, easy-to-use system is desired.
For optical dipole and lattice cold atoms experiments, a continuous wave (CW), far off-resonant wavelength around 1μm is often chosen (for red-detuned traps). This wavelength provides enough spectral offset for most atoms to avoid any optical excitation and is conveniently available on the market from Ytterbium-doped solid-state and fiber 바카라 실시간s with output powers scalable up to tens of watts. High power is advantageous as it increases the depth of the optical dipole trap. Other important 바카라 실시간 parameters include:
바카라 실시간 linewidth –a narrow line single-frequency emission is essential for well-defined interference patterns. The measurement time of the 바카라 실시간 linewidth must be taken into account when this parameter is specified.
Relative intens바카라 실시간y noise (RIN) –the lowest possible noise is desired as any fluctuations in intensity will increase the heating rates of the cold 바카라 실시간.
Frequency noise –the frequency noise of the 바카라 실시간 will influence the heating rates of the atoms as well, thus the minimal fluctuations are desirable, especially if the 바카라 실시간 in experiment is not frequency stabilized to external references.
Mephisto – 바카라 실시간s for the most demanding applications
Coherent’s approach towards CW high-stability 바카라 실시간 sources is based on a non-planar ring oscillator (NPRO) technology. Since its invention in Stanford University [8], this technology has been recognized as the lowest-noise CW 바카라 실시간 architecture available. It provides the basis for all Mephisto 바카라 실시간s, with the master oscillator cavity based exclusively on a monolithic crystal rather than discrete optical elements (Fig. 4). Such 바카라 실시간s deliver extremely low frequency and amplitude noise. Intrinsic linewidths of <1kHz over 100 of milliseconds are available due to 바카라 실시간’s extremely low phase noise. Furthermore, this narrow emission line can be tuned around its central emission frequency with high precision by adjusting the NPRO crystal temperature or by fine-tuning it with a fast integrated piezo transducer (PZT). It allows the user to have full control over the 바카라 실시간 emission – which is extremely important in atom cooling and trapping experiments. This control also enables locking the 바카라 실시간 to an external reference when even higher frequency stability is needed. For example, the user may wish to lock the 바카라 실시간 to an external high-stability cavity or iodine line by having access to frequency control of the 바카라 실시간.
Apart from a narrow linewidth and low phase noise performance, important for creation of efficient interference structures, Mephisto products also provide low amplitude noise, which is further improved by Noise Eater (NE) technology. As in many diode-pumped solid-state or fiber 바카라 실시간s, pump diodes and the relaxation oscillations are the prominent intensity noise contributors. The Noise Eater effectively eliminates these two components by providing a feedback signal to the pump diodes. For a more detailed description of the technology behind Mephisto products, please see [9].
Fig. 4.Schematic representation of NPRO crystal. Orange arrow indicates the pump light and blue arrows show the path of the 바카라 실시간 mode.
Due to its superior stability parameters, Mephisto is the 바카라 실시간 of choice in some of the most demanding low-noise 바카라 실시간 applications. This includes Gravitational Waves detection [10], interferometric measurements, low-signal heterodyning, metrology, and similar applications. Atomic physics experiments benefit especially from high-stability and high-power when off-resonant wavelengths are used to form sufficient depth of potential traps and high-precision stable optical lattices.
Output power straight from the NPRO master oscillator is commercially available up to 2W. At higher powers the 바카라 실시간 performance might be compromised by transverse and longitudinal mode instabilities due to thermal effects. However, the applications discussed in this whitepaper require much higher powers, namely, tens of Watts, while retaining ultra-narrow linewidth, low noise, and high-frequency stability.
Fig. 5.바카라 실시간herent Mephisto MOPA
Fig. 6.Schematic representation of Mephisto MOPA design
To overcome this power lim바카라 실시간ation, Coherent uses aMaster Oscillator Power Amplifier (MOPA)approach. The NPRO oscillator is used as a seed source in this configuration. The output of this seed 바카라 실시간 is amplified gradually by using up to four amplification stages (diode pumped neodymium vanadate crystals, Fig. 6). Because of the MOPA configuration, the parameters of the 바카라 실시간 are defined inside the seed 바카라 실시간, where the NPRO crystal is operated at an optimum power level.
The MOPA provides power amplification up to 55W at 1064nm with uncompromised stability of the standard Mephisto in a factory-integrated single-box solution. As a result, similar ultra-narrow linewidth, phase noise spectrum, and frequency tuning capabilities are available. Importantly to the cold atoms applications, the influence on the 바카라 실시간 amplitude noise is minimal – no additional noise is added at the frequencies above 50kHz. A small increase at lower frequencies is created by MOPA control electronics (See Fig. 7). Using RIN spectrum, the 바카라 실시간 noise-induced cold atoms heating rate in optical trap can be calculated [11] – Fig. 8. Due to low-intensity noise from Mephisto MOPA, the heating rate can be significantly lower as compared to other 바카라 실시간 technologies. Good beam parameters and extremely long coherence length (1km) makes the beam easy to manipulate in the experimental setup, especially where multiple beams are formed by beam splitters and retro-reflectors. Most of the scientific experiments using cold atoms are relatively complex, including tunable 바카라 실시간s, Zeeman slower, vacuum chambers, atom sources, related optoelectronics, etc. Thus it is important for us to provide a single-box solution which includes a fully integrated 바카라 실시간 system and easy, turn-key operation – in this way, the user can focus on the experiment rather than the maintenance of the 바카라 실시간. In addition to Mephisto MOPA, which is based on all-solid-state technology, Coherent also offers CW single-frequency fiber amplifiers through the NuAmp product line. NuAmp products provide power amplification up to 50W, enable beam delivery by fiber, and are available in the wavelength range of 1030 – 1110nm.
Fig. 7.Relative intensity noise (RIN) measured from the seed 바카라 실시간 and the output of MOPA at a power of 55W
Fig. 8.Cold atoms heating rate due to 바카라 실시간 intensity noise from the MOPA
Summary
Stable CW 바카라 실시간s are used in a number of different experimental methods for cold atom studies. Coherent Mephisto MOPA uses NPRO technology and well-established 바카라 실시간 power amplification techniques to provide highly stable 바카라 실시간 source which comes in a thoroughly field-tested, turnkey single-box solution. Ultra-narrow linewidth and market-leading phase and intensity stability parameters enable lowest noise and longest measurement times in experiments where optical dipole traps or optical lattices are used.