Optical resonant cavity device with cross cavity and its application

Abstract

An optical resonant cavity device (100) with a cross cavity, in particular for optically trapping atoms, comprising: a first linear optical resonant cavity (10), the first linear optical resonant cavity (10) extending along a first resonant cavity optical path (12) between first resonant cavity reflectors (11A, 11B) and supporting a first resonant cavity mode; a second linear optical resonant cavity (20), the second linear optical resonant cavity (20) extending along a second resonant cavity optical path (22) between second resonant cavity reflectors (21A, 21B) The invention relates to a carrier device for extending and supporting a second resonant cavity mode, wherein the first resonant cavity optical path (12) and the second resonant cavity optical path (22) span across a main resonant cavity plane; and a carrier device for carrying the first resonant cavity reflector (11A, 11B) and the second resonant cavity reflector (21A, 21B), wherein the first resonant cavity reflector (11) and the second resonant cavity reflector (21) are arranged so that the first resonant cavity mode and the second resonant cavity mode intersect each other to provide an optical lattice well (1) in the main resonant cavity plane. The carrier device comprises a monolithic separator (30), the monolithic separator (30) being made of ultra-low expansion material and comprising a first carrier surface (31) accommodating the first resonant cavity reflectors (11A, 11B) and a second carrier surface (32), the first carrier surface (31) accommodating the first resonant cavity reflectors (11A, 11B), the second carrier surface (32) accommodating the second resonant cavity reflectors (21A, 21B), wherein the first resonant cavity optical path (12) extends through a first separator hole (33) in the separator (30) between the first carrier surfaces (31), and the second resonant cavity optical path (22) extends through a second separator hole (34) in the separator (30) between the second carrier surfaces (32). In addition, an atom trapping method for constructing a two-dimensional arrangement of atoms, an atom trapping device such as an optical atomic clock, a quantum simulation and / or quantum computing device are described.

Description

Technical Field

[0001] The present invention relates to an optical resonant cavity device with a crossed cavity (cross-cavity resonator), in particular, for optically trapping atoms, for example, for use in an optical atomic clock comprising an optical lattice trap or in a quantum simulator, in particular a quantum gas microscope. In addition, the present invention relates to a method for using the optical resonant cavity device, for example, for providing reference atoms for an optical atomic clock or sample atoms in a quantum simulator or quantum computer. In addition, the present invention relates to an optical atomic clock, and a quantum simulator comprising an optical resonant cavity device. Prior art

[0002] This specification refers to the following prior art reference documents to illustrate the background technology of the present invention:

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[10] I. Bloch, J. Dalibard and S. Nascimbène, Quantum simulations with ultracold quantum gases, Nature Physics 8, 267 (2012);

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[11] IM Georgescu, S. Ashhab and F. Nori, Quantum simulation, Reviews of Modern Physics 86, 153 (2014);

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[16] CK Hong, ZY Ou and L. Mandel, Measurement of subpicosecond time intervals between two photons by interference, Physical Review Letters 59, 2044 (1987);

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[0024]

[22] RJ Lewis-Swan, MA Norcia, JRK Cline, JK Thompson and AMRey, Robust Spin Squeezing via Photon-Mediated Interactions on an Optical Clock Transition, Physical Review Letters 121, 070403 (2018).

[0025] As is known, the units of measurement in the International System of Units (SI) have recently been defined by a combination of fundamental physical constants. The next update of the SI system will change the definition of the second. The SI second is defined as the number of specific oscillations of a microwave transition between two hyperfine states of a caesium atom, measured using a so-called caesium fountain clock. In the past 15 years, a new standard based on the use of a caesium fountain in an optical lattice, the so-called Optical lattice clock ) has improved its stability and accuracy by two orders of magnitude [1]. For this reason, it is planned that the SI second will be redefined according to the optical standard in the next few years.

[0026] Optical lattice clocks have become so precise that the effects of general relativity can be observed directly by simply adjusting them a few centimeters above the Earth's gravitational field [1]. This capability opens up entirely new possibilities for direct measurements of the gravitational potential for applications in geodesy [2]. The increased precision of time measurements will also significantly improve the accuracy of global satellite navigation. Optical frequency standards are already being linked to quantum networks via ground-based fiber-optic networks. These networks will provide phase-coherent links between remote laboratories in Europe and internationally [1]. In the future, such links will enable the detection of gravitational waves on Earth-sized scales and will provide very long baseline interferometry for other astronomical or deep space observations.

[0027] All of these near-term applications of optical atomic clocks must rely on efficient, robust optical standards that must be compatible with handover operations on spacecraft, satellites, aircraft, or moving vehicles. Specifically, space-based systems will need to be resilient against strong accelerations during the launch phase and cannot be manually readjusted after launch. Therefore, in Earth-based quantum metrology laboratories, there is an interest in removing optical atomic clocks configured as optical lattice clocks from highly controlled environments and providing robust and / or transportable optical atomic clocks for routine applications.

[0028] A movable optical lattice clock has been realized in references [2, 3]. This optical lattice clock uses strontium atoms in a one-dimensional optical lattice, which is formed by reflecting an initial laser beam once and superimposing the reflected laser beam with the initial laser beam. The optical lattice clock uses a fixed retroreflector, but standard kinematic supports can also be used, which are susceptible to temperature drift and vibration and need to be readjusted after being subjected to strong acceleration. Although the optical lattice clocks described in references [2, 3] are mounted on a truck, such optical lattice clocks cannot be operated when they are moved. Specifically, the ISOC project aims to build a space-compatible optical lattice clock [4]. The collaboration aims to reduce weight and power consumption and improve long-term stability. However, a standard one-dimensional lattice using a retroreflected laser beam is currently used. The latest generation of optical lattice clocks [5, 6] use a two-dimensional optical lattice and a Fermi degenerate gas of strontium atoms at the focus of a high-resolution microscope objective. The device is almost identical to the quantum gas microscope used for quantum simulation (see below). However, this laboratory-based standard still uses an optical lattice with a retroreflected beam and is limited by the lattice beam waist (1 / e 2 The optical power requirement of a beam radius of about 100 μm is limited, thus limiting the number of reference atoms and the signal-to-noise ratio of the optical lattice clock.

[0029] Another major application of optical lattices is in the field of quantum simulation [7] with ultracold atoms in optical lattices [8, 9]. Quantum simulator Atoms are trapped and manipulated by lasers in an optical lattice. To trap atoms, they are confined to the intensity maxima of a back-reflected laser beam that forms an optical lattice trap. Rather than simply detecting the clock transitions of trapped atoms, quantum simulators are used to study the quantum many-body dynamics that arise when atoms tunnel and interact in the optical lattice [8]. At temperatures below one millionth of a kelvin above absolute zero, the motion and interactions of atoms must be described using quantum mechanics.

[0030] Quantum simulators based on ultracold atoms are used to gain deeper insights into the dynamics of quantum mechanical models, such as the Hubbard model that describes the motion of electrons in crystals in condensed matter physics [9]. Advances in this area, for example, investigating the physics of quantum spin systems and more exotic phenomena beyond the scope of solid-state devices or computational approaches, are described in References [9, 10, 11]. Much of the progress in the past decade has been made possible by new microscopy techniques that allow the observation and control of individual atoms in the plane of high-resolution imaging systems [12, 13]. However, even with these new techniques, it remains very challenging to construct cryogenic quantum systems with more than a few dozen atoms while maintaining complete control over each atom.

[0031] One of the main challenges in quantum simulations with ultracold atoms in optical lattices is to make the trapping conditions more uniform. As mentioned above, optical lattices are usually formed by back-reflected laser beams. Any such beam must have a finite extent transverse to its propagation direction. The transverse intensity distribution of the laser beam causes lateral variations in the depth of the formed optical lattice. This depth variation then causes variations in the tunneling rate and interaction parameters. Since the system parameters vary with position, it is impossible to achieve a completely uniform quantum system in an optical lattice. The inhomogeneity translates into a finite range of desired quantum phases, such as Mott insulators, in which the atoms are arranged in such a way that a single atom occupies each lattice site. The Mott insulating phase is the lowest entropy quantum phase currently achievable and is often used as the initialization for quantum simulators. The fidelity of such simulations is limited by the finite size and defects of the initial Mott insulator. To do this, it is necessary to reduce the optical lattice inhomogeneity and increase the achievable Mott insulator size.

[0032] The most homogeneous optical lattice systems have been demonstrated in quantum gas microscope setups [9]. Here, the high spatial resolution allows local modification of the optical lattice and can compensate for some inhomogeneities due to the lateral shape of the lattice laser beam. This compensation is particularly important for Fermi atoms

[14] , which are distributed over a larger area of ​​the optical lattice compared to Bose atoms (due to the Pauli exclusion principle). State-of-the-art quantum gas microscopes with Fermi atoms can produce nearly defect-free atomic checkerboard patterns of about 30*30 atoms (this is the Mott insulating phase of the Hubbard model) [14, 15]. These dimensions are limited by the lateral extent of the laser beam that generates the optical lattice potential, which in turn is limited by the laser power provided by high-power solid-state lasers at 1064nm (about 50W). State-of-the-art quantum simulations using such Mott insulators as starting points have been limited to the degree of identity of the lattice positions. The standard quantum optical method used to quantify the degree of identity of particles is the Hong-Ou-Mandel effect

[16] . In this effect, two identical photons are brought to the beam splitter. If the photons are identical, they will always leave one of the ports of the beam splitter together. Thus, it is not possible to find one photon in one port and another in the other. This effect can be translated into massive particles and has been measured in quantum gas microscopy with bosonic particles

[17] . Since it was not possible to find more identical lattice positions in the past, such measurements were limited to perturbing two samples of four atoms each. Therefore, there is also interest in constructing larger optical lattice wells with improved uniformity for quantum simulation applications. The simplest way to achieve this can be based on simply increasing the lateral extent of the lattice laser beam. However, both quantum metrology and quantum simulation require the lattice to have extremely high amplitude and frequency stability. Increasing the beam size is challenging, because state-of-the-art quantum simulation laboratories already use the largest beam sizes achievable with the highest power lasers that meet the required stability criteria.

[0033] As an alternative to back-reflected laser beams, the above problems are even more challenging if resonant optical field enhancement is used to create the light trap. In this case, the light trap is set in an optical resonator, specifically at the waist of a resonant cavity mode of the optical resonator. To construct a two-dimensional light trap, an optical resonator with a crossed cavity is used, for example as described in reference

[18] . A conventional optical resonator with a crossed cavity consists of two pairs of resonant cavity mirrors located on the same substrate. In order to obtain sufficient trapping stability, such a device is limited to a small mode waist diameter in the trap of about 200 μm, which limits the number of atoms and the signal-to-noise ratio for quantum simulation applications. In addition, when the optical resonator is operated in a vacuum, the geometry of the resonant cavity may drift due to the creation of the vacuum or heating after the vacuum is created.

[0034] Purpose of the Invention

[0035] The object of the present invention is to provide an improved optical resonant cavity device for optically trapping atoms, thereby circumventing the disadvantages of conventional technologies. Specifically, the object of the present invention is to provide an improved optical resonant cavity device, which has the following characteristics: has a robust structure; allows mobile operation; maintains stability even under strong acceleration; provides uniform trapping conditions; allows the construction of lattice wells in multiple dimensions; and / or allows the construction of lattice wells that increase the size and number of trapped particles. In addition, the object of the present invention is to provide an improved method for optically trapping atoms using an optical resonant cavity device. In addition, the object of the present invention is to provide an improved atom trapping device for constructing two-dimensional arrangements of atoms and their applications in optical atomic clocks, quantum simulators or quantum computers. Summary of the invention

[0036] These objects are solved accordingly by an optical resonator device having the features of the main claim, by a method for optically trapping atoms using said optical resonator device, by an atom trapping device such as an optical atomic clock, and by a quantum simulator and / or a quantum computer using said optical resonator device. Preferred embodiments and applications of the invention are set forth in the dependent claims.

[0037] According to a first general aspect of the present invention, the above object is solved by an optical resonant cavity device with a crossed cavity, the optical resonant cavity device comprising: a first linear optical resonant cavity (first cavity), the first linear optical resonant cavity extending along a first linear resonant cavity optical path between first resonant cavity mirrors and supporting at least one first resonant cavity mode; a second linear optical resonant cavity (second cavity), the second linear optical resonant cavity extending along a second linear resonant cavity optical path between second resonant cavity mirrors and supporting at least one second resonant cavity mode. Each of the first optical resonant cavity and the second optical resonant cavity comprises a pair of resonant cavity mirrors. Each resonant cavity mirror comprises a mirror substrate and a reflective coating, the reflective coating facing the other resonant cavity mirror of the associated optical resonant cavity. Preferably, the reflective coating comprises a stack of dielectric layers, the stack of dielectric layers being selected so as to obtain a specific reflectivity for an operating wavelength. The first optical resonant cavity and the second optical resonant cavity cross each other, i.e. the first resonant cavity optical path and the second resonant cavity optical path intersect each other. The first resonant cavity mode and the second resonant cavity mode cross each other. The plane accommodating the first resonant cavity optical path and the second resonant cavity optical path is here denoted as the main resonant cavity plane.

[0038] Furthermore, the optical resonant cavity device comprises a carrier device, which supports the first resonant cavity mirror and the second resonant cavity mirror. The first resonant cavity mirror and the second resonant cavity mirror are fixedly placed on the carrier device. Due to the crossed configuration of the first cavity and the second cavity, an optical lattice well can be provided in the main resonant cavity plane, wherein the first resonant cavity mode and the second resonant cavity mode (lattice laser beam) cross each other. The carrier device and the first resonant cavity mirror and the second resonant cavity mirror connected to the carrier device are adjusted so that in the case of light field coupling into the first optical resonant cavity and the second optical resonant cavity, the light field is superimposed and field extrema providing an optical lattice well are generated. The optical lattice well is part of the crossed cavity, wherein the atomic trapping light field extrema can be generated by the laser propagating in the resonant cavity. Preferably, the first optical resonant cavity and the second optical resonant cavity have equal geometry in terms of resonant cavity length and mirror shape, so that the first optical resonant cavity and the second optical resonant cavity can support the same or at least sufficiently similar resonant cavity modes.

[0039] According to the invention, the carrier device comprises a monolithic separator, the monolithic separator is made of a solid ultra-low expansion material and comprises a first carrier surface (i.e. a first pair of carrier surfaces) and a second carrier surface (i.e. a second pair of carrier surfaces), the first carrier surface accommodating the first resonant cavity reflector and the second carrier surface accommodating the second resonant cavity reflector. The separator is a monolithic separator, i.e. made of a single integral block of material. The monolithic separator comprises an ultra-low expansion material, i.e. a material having no thermal expansion or having a minimum thermal expansion coefficient. Preferably, the material of the monolithic separator has a zero-crossing thermal expansion function under the temperature conditions of operating the optical resonant cavity device, preferably under room temperature or low temperature conditions. The carrier surface comprises a surface portion of the separator. Preferably, the carrier surface is a planar surface portion extending perpendicular to the plane of the main resonant cavity. The carrier surface is an outer side surface of the separator. Preferably, the reflector substrate of the resonant cavity reflector is made of the following materials: a transparent material allowing light to be coupled into the resonant cavity; and a material having a thermal expansion coefficient equal to or matching the thermal expansion coefficient of the separator material at the same time. Furthermore, according to the present invention, the first resonant cavity optical path extends through a first separator hole in the separator between the first carrier surfaces, and the second resonant cavity optical path extends through a second separator hole in the separator between the second carrier surfaces. The first separator hole and the second separator hole are hollow passages passing through the separator, and the hollow passages are divided into two at their intersection. The inner diameter of each of the first separator hole and the second separator hole is respectively larger than the mode diameter of at least one first resonant cavity mode and at least one second resonant cavity mode. Generally, the separator hole can also be understood as a hole or channel passing through the separator and radially completely closed by the separator material.

[0040] Preferably, the separator has a plate shape extending along the main resonant cavity plane. The dimension of the separator perpendicular to the main resonant cavity plane is denoted as the thickness of the separator. The thickness of the separator is selected so that the separator has sufficient mechanical stability and the carrier surface has sufficient dimensions to attach the resonant cavity mirror.

[0041] According to a second general aspect of the present invention, the above-mentioned object is solved by an atom trapping method for constructing a two-dimensional arrangement of atoms, wherein an optical resonant cavity device according to the above-mentioned first general aspect of the present invention is used. The atom trapping method comprises the following steps: constructing an optical lattice well in a region where a first resonant cavity mode and a second resonant cavity mode intersect each other. The optical lattice well is constructed by coupling a laser beam into a first optical resonant cavity and a second optical resonant cavity. Due to the resonant geometry of each resonant cavity, the resonant cavity modes superimposed at the intersection of the resonant cavities are supported, thereby forming the optical lattice well. The atom cloud in the optical resonant cavity device is trapped in the optical lattice well. The atoms can be introduced into the optical resonant cavity device before or after the creation of the optical lattice well. When the atoms are located at the field extremes of the optical lattice well, the metrology and / or simulation applications of the trapped atoms can be realized as described below.

[0042] Preferably, the step of creating the optical lattice trap comprises coupling a first continuous wave (CW) and a second continuous wave (CW) laser beam into the first optical resonant cavity and the second optical resonant cavity, respectively, so that the optical lattice trap is formed by overlapping the first resonant cavity mode and the second resonant cavity mode at the intersection of the first separator hole and the second separator hole. According to a preferred application of the present invention, the following steps may be provided: imaging the atoms trapped in the optical lattice trap using an imaging device; exciting and detecting transitions between energy states of the trapped atoms; and / or utilizing interactions between the atoms for quantum simulation and / or quantum computing purposes.

[0043] Advantageously, the optical resonant cavity device of the present invention allows for large mode diameters for two well-overlapping optical light field modes. The optical resonant cavity device is suitable for vacuum operation and has extremely high stability, which does not yet exist in the field of optical lattice traps. The use of the separator facilitates the adjustment of the optical resonant cavity (single adjustment, initial adjustment of each resonant cavity) and provides stability and durability after the initial adjustment. In contrast to conventional techniques (e.g., reference

[18] ), the resonant cavity mirrors are not mounted in a mirror fixture, but are directly fixed to the separator in a two-dimensional planar manner. The present invention uses the separator as a single mirror holder without the need for movable parts that carry all the mirrors of the first optical resonant cavity and the second optical resonant cavity. Any instability introduced by multiple mirror holders is avoided.

[0044] In particular, the present invention addresses the challenges faced by quantum metrology and quantum simulation of ultracold atoms in optical lattices. These challenges are solved by reflecting the lattice laser beam multiple times between high reflectivity mirrors. As a result, such an optical resonant cavity enhances the strength of the optical lattice and allows the use of large beams. Both optical frequency standards and quantum simulators greatly benefit from the use of optical lattices in multiple dimensions. To this end, the present invention provides two such optical cavities with different axes that are preferably orthogonal, so that the generated standing waves completely overlap. For example, the construction of two large resonant cavity beams with good overlap at visible and / or near-infrared wavelengths places extremely high demands on the mechanical precision of the support structure of the resonant cavity mirrors. The inventors have demonstrated that the present invention overcomes this technical challenge. The present invention uses a resonant cavity component of a completely passive design, i.e. the resonant cavity does not contain materials that can move relative to each other. Preferably, all components of the resonant cavity device are thermally stable solids, in particular glass, which are optically bonded in an adhesive-free manner. Ultra-low expansion glass ensures that the arrangement of the optical lattice is stable and is not affected by heat. This structure also makes the present invention resilient against strong accelerations and makes it meet the requirements of extreme high vacuum (XHV). By changing the parameters of the reflective coating on the reflector substrate of the resonant cavity reflector, in particular the material and thickness of its dielectric layer, the invention can be applied to any optical wavelength compatible with high-quality thin-film technology. These features solve many technical problems in traditional quantum simulation. However, they also make the invention particularly suitable for inclusion in any transportable optical lattice clock, in particular for space missions.

[0045] According to a preferred embodiment of the present invention, the first resonant cavity reflector is bonded to the first carrier surface in an adhesive-free manner and the second resonant cavity reflector is bonded to the second carrier surface in an adhesive-free manner. Advantageously, any mechanical or thermal instability of the optical resonant cavity device is minimized in an adhesive-free manner. Particularly preferably, the first resonant cavity reflector and the second resonant cavity reflector are optically bonded to the first carrier surface and the second carrier surface, respectively. Optical bonding has the advantage of a simple process for implementation.

[0046] According to another preferred embodiment of the present invention, at least one of the first pair of resonant cavity mirrors comprises a curved mirror (first curved mirror), and at least one of the second pair of resonant cavity mirrors comprises a curved mirror (second curved mirror). Preferably, the curved mirror is a spherical mirror. Providing the curved mirror provides support for all Hermite-Gaussian modes of the resonant cavity TEM. ij To construct the optical lattice trap, the lowest order Hermite-Gaussian mode TEM is used. 00, that is, the first resonant cavity reflector and the second resonant cavity reflector support the Gaussian resonant cavity laser beam. Preferably, the first optical resonant cavity and the second optical resonant cavity are designed so that the first resonant cavity mode and the second resonant cavity mode intersect each other at a central portion, wherein the two modes have equal or sufficient diameters.

[0047] According to a particularly preferred embodiment of the present invention, the first curved reflector and the second curved reflector have a selected radius of curvature, and the selected radius of curvature enables the optical lattice well to have a size of 2*w0 in the plane of the main resonant cavity, and the size is at least 300 μm, in particular at least 400 μm, wherein w0 is 1 / e of the first resonant cavity mode and the second resonant cavity mode. 2 Waist radius.

[0048] Advantageously, the invention can provide a waist of, for example, about 400 at the desired wavelength. Implementation of the invention increases the system size by a factor of 16. Using 16 times more atoms directly increases the signal-to-noise ratio of, for example, a frequency standard using the invention by a factor of 4 compared to using only a typical average. The signal-to-noise ratio can be increased by a factor of 16 using quantum metrology techniques

[22] . The invention can be used directly to increase the uniformity, thereby also increasing the number of identical sites by a factor of 16. This factor directly increases the fidelity of any state-of-the-art quantum simulation of Bose or Fermi atoms, since it makes the particles more identical.

[0049] If each resonant cavity is a combination of one of the curved mirror and the plane mirror, that is, if the first resonant cavity mirror includes the first curved mirror and the first plane mirror, and the second resonant cavity mirror includes the second curved mirror and the second plane mirror, advantages are obtained in superimposing the resonant cavity modes and constructing the optical lattice well.

[0050] Preferably, the ultra-low expansion material has thermal expansion properties, such as ultra-low expansion glass (trade name). Particularly preferably, the monolithic separator is made of a piece of ultra-low expansion glass. Alternatively, the monolithic separator can be made of other glass materials that have no thermal expansion or have negligible thermal expansion properties, such as ultra-low expansion glass. As another alternative, the separator can be made of crystalline silicon. Since the latter embodiment requires a silicon reflector substrate, there is no differential thermal expansion property between the reflector and the separator, and silicon is opaque to visible light, but transparent to telecommunication wavelengths (e.g., 1550nm), and this embodiment is suitable for applications in the infrared wavelength range. In addition, the crystalline silicon space embodiment operates at 100K, where a zero crossing of silicon thermal expansion is obtained.

[0051] According to another preferred embodiment of the present invention, if the first separator hole and the second separator hole are orthogonal to each other in the main resonant cavity plane, an advantage is obtained in terms of a uniform distribution of local field extrema of the optical lattice well. Otherwise, if the first separator hole and the second separator hole are not orthogonal to each other, another deformed distribution of local field extrema of the optical lattice well can be created if required for a specific application of the optical resonant cavity device.

[0052] Particularly preferably, the first separator hole and the second separator hole are arranged in the separator in a mirror-symmetrical manner with respect to a normal plane oriented perpendicularly to the main resonant cavity plane. Advantageously, the stability of the separator increases with the symmetry of the separator holes. In addition, possible mechanical vibrations of the separator are also symmetrical with respect to the normal plane, so that the influence of the mechanical vibrations on the construction of the optical lattice well is minimized.

[0053] According to another advantageous embodiment of the invention, the monolithic separator has a third separator hole, which extends perpendicularly to the main resonant cavity plane and intersects the first and second separator holes at their intersection. Advantageously, the third separator hole fulfils a dual function. Firstly, it facilitates evacuation of the interior space of the separator. The evacuation can be accelerated and / or uneven evacuation can be avoided. Secondly, the third separator hole provides an additional optical access to the optical lattice well. Therefore, according to a particularly preferred embodiment of the invention, the optical resonant cavity device further comprises an imaging device, such as an optical microscope, which is arranged to image the optical lattice well along the third separator hole. Preferably, the third separator hole has a diameter that is larger than the diameter of the first and second separator holes, in particular allowing the front lens of the imaging device optics to be positioned just adjacent to the diameter of the optical lattice well. Advantageously, this allows optical monitoring and / or spectroscopic investigation of the optical lattice well with a large numerical aperture and high resolution.

[0054] Additionally or alternatively, the third separator hole may be arranged to accommodate a third optical path, the direction of which deviates from the plane of the main resonant cavity; and a retroreflector is arranged to generate a trapped light field along the third optical path. In this case, preferably, the third separator hole intersects the entire separator so that the laser light for confining the optical lattice well perpendicular to the plane of the main resonant cavity can be introduced from the side opposite to the imaging device. The retroreflector may be provided by a portion of the front lens of the imaging device optics.

[0055] If the monolithic separator has at least one further separator hole, which extends parallel to the main resonant cavity plane and intersects the first and second separator holes at their intersection, further advantages are obtained in coupling an additional measurement beam into the optical lattice trap (e.g. for interrogating the trapped atoms or their interactions). According to a particularly preferred example, the monolithic separator has two further separator holes, which are arranged symmetrically with respect to the arrangement of the first and second separator holes. Furthermore, advantages in the mechanical properties of the separator are obtained by utilizing the symmetry of the two further separator holes.

[0056] Another particular advantage of the present invention stems from the fact that there are no particular restrictions on the outer shape of the separator of the optical resonant cavity device. The outer shape of the separator can be selected according to the specific application conditions of the optical resonant cavity device, such as a rectangular separator shape, a polygonal separator shape or a cylindrical separator shape, that is, the footprint of the separator plate parallel to the main resonant cavity plane can have, for example, a circular, elliptical, rectangular or polygonal or other shape.

[0057] According to a particularly preferred embodiment of the invention, the monolithic separator has the shape of an octagon extending parallel to the plane of the main resonant cavity, wherein the first carrier surface and the second carrier surface are lateral side surfaces of the octagon. The octagon is particularly advantageous in providing a plurality of separator holes, hole symmetry and possible body vibration symmetry.

[0058] According to another preferred variant of the invention, the first resonant cavity reflector and the second resonant cavity reflector have a dielectric coating, which provides a reflectivity of at least 99%. This confinement allows the laser beam to be efficiently coupled into the cross cavity and to resonantly enhance the laser beam with a fineness of at least 300 and an enhancement of at least 100 at the same time. Particularly preferably, the dielectric coating is designed to provide the reflectivity of at least 99% for multiple resonant wavelengths of the first optical resonant cavity and the second optical resonant cavity. Preferably, the geometric dimensions of the optical resonant cavity device are selected in at least one of the following intervals. Preferably, the dimension (e.g. diameter (length)) of the separator along the plane of the main resonant cavity ranges between 3 cm and 20 cm. Additionally or alternatively, the diameter of the first resonant cavity reflector and the second resonant cavity reflector may range between 10 mm and 30 mm. This diameter range is preferred based on the large mode diameter at the intersection of the first optical resonant cavity and the second optical resonant cavity and the ability to polish curved resonant cavity reflectors. Additionally or alternatively, each of the first pair of cavity mirrors and the second pair of cavity mirrors comprises a curved mirror having a radius of curvature ranging from 1 m to 20 m. Additionally or alternatively, the first pair of cavity mirrors and the second pair of cavity mirrors are arranged in an aligned manner so that the reflected laser beam in the first optical resonant cavity and the second optical resonant cavity deviates from the center of the hole by less than 25% of the diameter of the hole. Additionally or alternatively, the laser beam in the cross-resonant cavity deviates from the central resonant cavity axis by no more than 1 mm.

[0059] According to a third general aspect of the present invention, the above object is solved by an atom trapping device, which is suitable for constructing a two-dimensional arrangement of atoms and includes an optical resonant cavity device according to the first general aspect of the present invention. The atom trapping device also includes: a laser device, which is suitable for coupling a continuous wave laser beam into the first optical resonant cavity and the second optical resonant cavity; an atom source and supply device, which is connected to the optical resonant cavity device and is suitable for generating an atom cloud and introducing the atoms into the optical resonant cavity device, for example, through an optical trap and / or a magnetic trap; an imaging device, which is suitable for imaging the optical trap lattice in the optical resonant cavity device.

[0060] According to a first main application of the invention, the atom trapping device is an optical atomic clock. With this embodiment, the imaging device is arranged to detect optical transitions in the trapped atoms (e.g., Sr atoms). According to another main application of the invention, the atom trapping device is configured as a quantum simulation or quantum computing device. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Further details and advantages of the invention are described below with reference to the accompanying drawings, which schematically show:

[0062] Figure 1 : A first embodiment of the optical resonant cavity device provided by the present invention;

[0063] Figure 2 : Other features of the embodiments of the optical resonant cavity device provided by the present invention;

[0064] Figure 3 and Figure 4 : Illustration of mode tuning in an optical resonant cavity device;

[0065] Figure 5 : Features of an embodiment of the atom trapping device provided by the present invention;

[0066] Figure 6 : An embodiment of the apparatus for manufacturing an optical resonant cavity device provided by the present invention;

[0067] Figure 7 : Example of an overlay measurement after assembling the optical resonant cavity device. DETAILED DESCRIPTION

[0068] The features of a preferred embodiment of the invention are described below with reference to the configuration of the optical resonant cavity device and the structure of the atom trapping device. Since the application details of the invention, such as the details of operating an optical atomic clock or a quantum simulator, are implemented in a manner known per se from the prior art, they will not be described below. The implementation of the invention is not limited to the embodiments shown, for example with respect to the octagonal shape and / or dimensions of the separator and the features of the reflector, but accordingly the modified features covered by the claims of the invention can be utilized.

[0069] Cross-cavity design of optical resonant cavity device

[0070] Figure 1 and Figure 2 A side view of an embodiment of an optical resonant cavity device 100 of the present invention is shown ( Figure 1 ) and multiple perspectives ( Figure 2 A to Figure 2 E), the optical resonant cavity device 100 comprises a first crossed optical resonant cavity 10 , a second crossed optical resonant cavity 20 and a separator 30 . Figure 2 A shows a top view of the separator 30 with the resonant cavity mirror attached, Figure 2 B to Figure 2 D shows an illustrative side view of the separator 30 (without the reflector).

[0071] One or more "cross cavities" of the first optical resonant cavity 10 and the second optical resonant cavity 20 are provided by an ultra-low expansion glass octagonal separator 30, two curved mirrors 11A, 21A and two flat mirrors 11B, 21B. The cavity mirrors 11A, 11B, 21A, 21B are fixed to a first support surface 31 and a second support surface 32 provided by four of the eight side surfaces of the octagonal separator 30.

[0072] The material properties of the octagonal spacer advantageously determine the stability and robustness of the cross-cavity resonator design. According to a preferred embodiment, the spacer material is Corning 7972 ultra-low expansion (ULE) glass (trade name), but glasses from other manufacturers can also be used as long as such glasses have similar small thermal expansion properties. The coefficient of thermal expansion (CTE) of ULE glass is specified as (0±30) ppb / K under operating temperature conditions ranging from 5°C to 35°C. Even under the maximum possible operating temperature conditions ranging from -100°C to +160°C, the CTE remains below 1 ppm / K. The CTE determines the length stability of the octagonal spacer 30 and thus the frequency stability of the resulting optical cavity. In addition, temperature inhomogeneities can induce stresses in the spacer, resulting in effective angles and thus affecting mode overlap. In addition to vacuum compatibility, this is another reason why the present invention relies on contacting the reflector in an adhesive-free manner. Any adhesive has much worse thermal expansion properties than ULE glass, which can make mode overlap very sensitive to temperature fluctuations.

[0073] Figure 1 An example of a mounting structure (clamp) 50 that can be used to mount the optical resonant cavity device 100 in a vacuum chamber 60 is schematically shown. The mounting structure 50 includes four screws 51 for connecting a clamp 53 to a wall 61 of the vacuum chamber 60. Stainless steel balls 52 are arranged to symmetrically transfer forces between the separator 30 and the mounting structure 50 at four different points on the separator 30. The separator 30 is aligned with a vacuum inspection hole 62 in the wall 61. The vacuum inspection hole 62 is made of glass, and the wall 61 is made of steel.

[0074] The first resonant cavity optical path 12 extends through a first separator hole 33 in the separator 30 between the first carrier surfaces 31, and the second resonant cavity optical path 22 extends through a second separator hole 34 between the second carrier surfaces 32. The first resonant cavity optical path 12 and the second resonant cavity optical path 22 define the main resonant cavity plane (xy plane), and they form the optical lattice well 1 ( Figure 2) intersect each other at the symmetry center of the separator 30. A third separator hole 35 having a third resonant cavity optical path 36 extends perpendicular to the main resonant cavity plane (xy) and intersects the first separator hole 33 and the second separator hole 34 at the intersection of the two separator holes. The separator 30 has two other separator holes 37, which extend parallel to the main resonant cavity plane (xy) and are orthogonal to the first separator hole 33 and the second separator hole 34 at the intersection of the two separator holes.

[0075] like Figure 3 As shown, each combination of curved mirrors (11A, 21A) and flat mirrors (11B, 21B) forms an optical resonant cavity having Hermite-Gaussian modes. The mirrors 11A, 11B, 21A, 21B are attached to the separator 30 so that the lowest order Hermite-Gaussian mode (TEM) of each axis 00 The molds) intersect each other in the octagonal central third separator hole 35.

[0076] Each resonator mirror 11A, 11B, 21A, 21B comprises, for example, a fused silica mirror substrate with a diameter of 12.7 mm and a mirror coating, which are applied to the front mirror surface facing the first optical resonator 10 and the second optical resonator 20, respectively. In order to attach the mirrors 11A, 11B, 21A, 21B to the first carrier surface 31 and the second carrier surface 32, all mirror substrates have an uncoated annulus surrounding the mirror coating. The annulus is an interferometrically flat annular surface that allows the mirror to be attached to the separator 30 in an adhesive-free manner. Instead, the mirror is bonded to the separator 30 using van der Waals forces by a process called optical contact. The mirror front surface of appropriate shape, including the uncoated annulus and the mirror coating, can be manufactured by existing polishing and deposition techniques and tested with an optical interferometer (e.g., Zygo PTI250).

[0077] The curved surface of the curved mirrors 11A, 21A has a very large radius of curvature R of about 10 m. Such a large radius is preferred because the TEM of the cavity 00 Modulo 1 / e 2 The diameter 2w0 is determined according to the following equation

[0078]

[0079] Wherein, is the wavelength of the laser coupled into the optical resonator, and L = 50 mm is the cavity length of the optical resonator. For the representative near-infrared wavelength λ = 813 nm used in strontium optical lattice clocks, equation (1) predicts the mode diameter at the intersection of holes 33, 34 at 850 μm. Such a large mode diameter is achieved by a mirror with a radius of curvature of 10 m. Polishing the annulus to a mirror substrate with a radius of 12.7 mm is technically challenging. The reason for this difficulty can be understood by calculating the depth of the central curved surface area of ​​the surface. Assuming the diameter of the curved surface area is D, the depth d of the spherical area can be calculated according to the following equation

[0080]

[0081] For a mirror substrate with a diameter of 12.7 mm and a contact annulus with a width of 2 mm, equation (2) results in a depth of less than 1 micron. Such a small depth can be achieved by extreme care when polishing the annulus into a curved substrate, while avoiding degradation of the curvature in the process. In comparison, a representative 1 inch substrate with a radius of curvature of 50 cm for a representative laser reference cavity can be flattened by about 160 μm to obtain a uniformly larger spherical area and a larger annulus. For the geometry of the present invention, reducing R to 50 cm will result in a mode diameter of 360 μm at a wavelength of 689 nm. If a reduction in optical lattice uniformity can be tolerated in a particular application of the present invention, a reduction in mode diameter of more than a factor of 2 is acceptable. Preferably, the large radius of curvature results in strict manufacturing precision requirements for the octagonal separator 30 to ensure that both TEM 00 The modes overlap well. For radii of curvature exceeding one meter, each mode has a relative angle of less than a few arc seconds between the mirrors, allowing the mode to be generated in the center of the mirror without being pinched by the 4 mm diameter hole in the spacer. Figure 3 As shown, the mode shift is calculated according to the following equation

[0082] Δh=R sinβ (3)

[0083] As can be seen from equation (3), the amount of mode transfer is given by the relative angle β between the mirror surfaces and the radius of curvature R. This relationship is independent of the length of the separator 30 along the optical resonant cavity. Since a large R of, for example, up to 10.2 m is used, and in order to minimize the amount of residual mode transfer, the specified relative angle is preferably limited to 1 arc second on the relative planes of the separator 30 with 4 mm holes 33, 34.

[0084] In addition, the upper reference surface 38 (see Figure 2) and the angle between the surface pair 31, 32 assigned to the reflectors is specified to be less than 30 arc seconds to provide an orthogonal mode to the surfaces when the octagonal spacer optically contacts the surfaces. This orthogonality constraint is determined by the following equation

[0085] Δh=L / 2tanγ (4)

[0086] where Y parameterizes the deviation from perfect orthogonality between the mirror surface and the upper reference surface 38. According to the present description, the resulting mode transfer can be limited to less than 4 μm.

[0087] Another preferred feature of the separator 30 design is the symmetry and size of the holes 33, 34, 35, 37. Larger holes will reduce the mechanical stability and thus reduce the material's resistance to deformation, thereby reducing the vibration eigenfrequency of the separator 30. According to this embodiment, the hole size is selected so that the lowest vibration eigenmode with a vibration frequency higher than the typical energy scale, such as 20kHz, is obtained in the quantum system formed when atoms are trapped in the optical lattice. This is preferred because vibration of the separator 30 at frequencies corresponding to these energy scales can cause high intensity heating, resulting in a loss of fidelity [19, 20]. Based on numerical simulations, the separator design can be adapted to other vibration frequency requirements by changing the hole size or the separator thickness.

[0088] The preferred characteristics of the thickness of the separator 30 in the z direction (perpendicular to the plane of the main resonant cavity) and the diameter of the central hole are selected so that the imaging device 40 (see Figure 1 ) can approach the final optical lattice well at the intersection of holes 33, 34. The resolution of any imaging system is proportional to its numerical aperture. The numerical aperture is limited by the thickness of the separator and the diameter of the third separator hole 35. On the other hand, the separator is at least thick enough to allow contact of the mirror substrate to the first carrier surface 31 and the second carrier surface 32 on its side. In addition, the vacuum pumping speed outside the center of the separator 30 is given according to the same numerical aperture considerations. For these reasons, preferably, the separator thickness and the center hole 35 diameter are determined as a compromise between all the above considerations.

[0089] The angular tolerance given by equation (3) also translates into a constraint on the substrate tolerance of the curved mirrors 11B, 21B. The mismatch angle between the curved area and the annular area results in the same amount of mode transfer as in equation (3). Figure 4It is intuitively shown how such "wedge" errors are produced by imperfect polishing. When the mirror is parallel to the spacer surfaces (first carrier surface 31 and second carrier surface 32) or in optical contact, the deepest part of the curved surface determines the position of the mold. Therefore, the wedge error is preferably limited to the same angular tolerance as the parallelism of the spacer surfaces.

[0090] Furthermore, it is also preferred that the reflective coating is applied to the curved mirror substrate after polishing is completed. During the coating process, the annular region is shielded so that no coating material is applied to the annular surface. The main reason for this measure is that the inventors have found that the bond strength between the coated surface and the separator is significantly lower than that of the uncoated surface. Applying the reflective coating after polishing has two further advantages: first, it prevents scratching of the reflective coating during the polishing process. Second, the spherical region can be re-polished without the reflective coating to maintain the ratio of the annular surface to the radius of curvature.

[0091] Embodiments of an atom trapping device

[0092] Reference below Figure 5 An embodiment of an atom trapping device 200 is described. Figure 5 The application as a movable optical lattice clock or lattice optics in quantum simulation is schematically shown. In general, the atom trapping device 200 comprises: an optical resonant cavity device 100 provided by the present invention; a laser device having two laser sources 210, 220, which are arranged and adapted to couple a continuous wave laser beam into a first optical resonant cavity and a second optical resonant cavity of the optical resonant cavity device 100; an atom source and supply device 230, connected to the optical resonant cavity device 100; an imaging device 240, adapted to image the optical trap lattice in the optical resonant cavity device 100; an interrogation laser 250. If its regulation is sufficient, a single laser source can be used instead of the two laser sources 210, 220. In addition, a control and measurement device 260 is provided, which is arranged to: control the components 210, 220, 230, 240; and / or collect and analyze measurement data. Preferably, the control and measurement device 260 comprises a computer unit. Other laser devices can be provided for manipulating and / or sensing atoms in the optical trap lattice in the optical resonant cavity device 100.

[0093] As described above, the cross-cavity design of the optical resonant cavity device 100 of the present invention is particularly suitable for implementation in a movable optical lattice clock. Since the present invention uses a monolithic material, such as highly stable glass, the cavity mode overlap will be stable for an infinite time. The cavity itself and the overlapping part will not be subject to shock, vibration or any short-term mechanical influence that will not damage the glass. Only long-term mechanical stress can change the overlap when applied in an asymmetric manner. This effect can be achieved by an appropriate mounting structure 50 (see Figure 1) is strongly suppressed, which is true for any laser reference cavity. A detailed example of how to set up a crossed cavity is described below.

[0094] On a satellite or space station, temperature fluctuations are expected to be larger than in a laboratory on Earth. The cavity partitions are made of, for example, ultra-low expansion (ULE) glass, which has a very small thermal expansion coefficient. For certain temperatures, this coefficient even exceeds zero, an effect that is exploited in the laser reference cavity. Therefore, even if temperature gradients change the relative angles of the mirrors, this results in negligible changes in the mode overlap. The resonant cavity also plays the role of building a cavity to enhance the power coupled into the resonant cavity. As mentioned above, this allows the use of larger beam diameters, resulting in larger system sizes. In addition to the larger system size, building a cross-cavity can also reduce the power required to produce a sufficiently deep lattice. Therefore, the present invention can be used with low-power diode lasers instead of high-power solid-state lasers, which is a preferred feature for space-based system applications.

[0095] As mentioned above, in the field of quantum simulation and quantum metrology, a one-dimensional optical lattice is created by focusing an incident beam and a retroreflector. The cavity is designed with a perfect overlap of the incident beam and the retroreflected beam. To obtain a three-dimensional lattice, three one-dimensional lattices must be overlapped. For the retroreflected beam, this leads to multiple degrees of freedom, which is very useful when dealing with 1 / e of about 100 μm. 2 The multiple degrees of freedom are sensitive to beam radius. Even state-of-the-art laboratory experiments using retroreflective lattices show drift over the course of a day

[20] .

[0096] Since the optical resonant cavity 100 itself is stable and does not change, the present invention only uses a simple alignment process of the input beam to the optical resonant cavity. The input beam is aligned with the optical resonant cavity device 100 to maximize the Gaussian transverse electric mode (TEM) through the optical resonant cavity device 100. 00 The process is much faster than arranging free-space optical lattices, which requires a complete experiment with the trapped atoms for each arrangement trial.

[0097] Laser beams are not necessarily perfectly Gaussian beams, especially when they are emitted directly by semiconductor lasers. The more optical components a laser beam passes through on its way to the atomic sample, the further its quality is degraded, mainly due to lens aberrations or scattering from dust particles. In contrast, the cross cavity of the present invention is able to filter and clean the modes at the atomic positions, and its vacuum mirrors are protected from contamination.

[0098] As mentioned above, improvements in lattice uniformity and beam diameter will therefore lead to increased fidelity of quantum simulators and optical lattice clocks.

[0099] Embodiment of the atom trapping method

[0100] Construct two well-overlapping, large-diameter, stable optical lattices as shown below. Figure 1 The embodiment shown is suitable as an ultracold atom quantum simulator or an optical lattice clock.

[0101] Figure 1 A schematic diagram of the device is shown, including the following dimensions, namely, a separator width a of about 50 mm, a width b of the central hole 35 of about 20 mm, a separator height c of about 15 mm, and a thickness d of the vacuum inspection hole 62 of about 5 mm. The cross-cavity optical resonant cavity device 100 is installed in a pressure below 10 -11 mbar on the vacuum side of the extremely high vacuum (XHV) vacuum chamber 60. This pressure range is not essential for the function of the optical resonant cavity device 100 (it works well under laboratory conditions), but is preferred to maximize the lifetime of atoms trapped in the constructed optical lattice well 1. In quantum simulation and quantum metrology, atomic lifetimes that are far higher than typical experimental time scales (up to tens of seconds) are used to achieve high fidelity. Figure 1 , the cross-cavity optical resonant cavity device 100 is clamped to a vacuum inspection hole 62, for example, a vacuum inspection hole with a thickness of 5 mm. In this example, the optical resonant cavity device 100 is clamped to the glass using four screws 51. The stainless steel balls 52 symmetrically transmit the force between the separator 30 and the mounting structure 50 at four different points on the separator 30. By applying the clamping pressure evenly and symmetrically to the separator 30, the mode overlap remains unchanged, which can be verified using the mode overlap measurement technique during assembly.

[0102] The high-resolution microscope objective 41 of the imaging device 40 (high-resolution microscope) is installed as close as possible to the center of the optical resonant cavity device 100 to use the largest possible optical aperture. The objective 41 has a custom design that corrects the spherical aberration caused by the presence of the inspection hole.

[0103] Then, an optical lattice in the object plane of the imaging device 40 is generated by coupling the laser into the two resonant cavity modes of the cross cavity. Preferably, the laser frequency is stabilized to the corresponding cavity (optical resonant cavity 10, 20) mode using, for example, the standard Pound-Drever-Hall method. In order to improve the quality of the optical image collected with the imaging device 40, the atoms can be more tightly confined in the vertical direction. Additional confinement can be achieved by propagating a third optical lattice from the bottom through the third separator hole 35 of the separator 30. In order to further improve the insensitivity of the imaging system 40 to the residual differential movement between the cross cavity and the imaging optics, the vertical beam should be back-reflected from the final optical surface of the microscope objective 41. This is achieved by customized optical coatings for the vacuum inspection hole 61 and the front lens of the microscope objective 41.

[0104] In one of two ways (illustrated by Figure 7 The ultracold atoms are transported to the center of the cross cavity (indicated by 230 in FIG. 1 ), thereby loading the ultracold atoms into the generated three-dimensional optical lattice. A first option is to transport the atoms into the cavity using another horizontal optical dipole trap generated by a non-retro-reflecting laser, such as through another separator hole 37 (see FIG. Figure 2 ). The atoms can be transported to the region where the optical lattice is formed by transmitting a laser beam through one of four 5 mm horizontal holes and shifting its focus

[21] from the preparation area to the center of the cross cavity. A second option is to build a magneto-optical trap (MOT) below the cross cavity and then transfer them upwards by changing the zero point of the trap magnetic field. In either case, the depth of the optical lattice needs to be increased slowly while the transport trap is closed to achieve optimal transport of atoms. When transferring directly from the MOT, an intermediate evaporative cooling step can be used to reduce the atomic temperature. If the optional vertical lattice is used, the monolayers in the object plane can be separated by using a vertical magnetic field gradient. This gradient removes individual atomic layers, heating them with the resonant laser until they are ejected from the optical lattice.

[0105] Once the monolayer is isolated, experiments can be performed in a horizontal two-dimensional lattice. For quantum simulations, additional laser beams and magnetic fields can be used to control the evolution of atoms as they tunnel through and interact in the lattice. For optical frequency standards, atomic tunneling can be prevented by increasing the horizontal lattice depth and then interrogated using a spectral laser (e.g., through other separator holes 37). Preferably, a camera is used to take fluorescent images of the atoms during and / or at the end of the process. In an optical frequency standard, resolving individual lattice positions may not be as important as in a quantum simulator, and photomultiplier tubes can be used to detect spatially integrated atomic signals. Even in this case, high optical resolution is still beneficial because it maximizes the signal-to-noise ratio of the atomic signal. Once the experiment has been performed, the atoms can be removed by turning off the optical lattice, and a new sample can then be prepared as described above.

[0106] The present invention maximizes the optical access available for steering the beam by providing a large central hole 35 and four horizontal 5 mm holes 33, 34, 37. The central hole 35 is 20 mm in diameter, determined as a compromise between mechanical stability (and high acoustic eigenfrequency) and the need for optical access and vacuum pumping speed at the center of the cross cavity.

[0107] Installing and assembling the optical cavity device

[0108] Assemble the optical resonant cavity device 100 and use Figure 6The quality of the mode overlap is verified by the mounting device 300. Using the mounting device 300, the mirror is attached to the octagonal separator 30 in a determined manner while the quality of the mode overlap is monitored.

[0109] Preferably, the spacer and mirror are cleaned prior to mounting to ensure that the two surfaces can be bonded. While there are special repolishes that can promote optical contact between two flat, smooth glass surfaces, it is best not to use such repolishes because their outgassing properties under XHV conditions are unknown. For this reason, a cleaning procedure similar to that used in semiconductor manufacturing is used.

[0110] The separators are cleaned in a beaker of RCA1 cleaning solution consisting of destabilized hydrogen peroxide (30%), ammonium hydroxide (28-30%), and HPLC-grade or semiconductor-grade water in a 1:1:5 ratio by suspending them on a stainless steel wire. The solution is boiled at 80°C for 15 minutes in a fume hood. The beaker is then suspended in an ultrasonic bath with HPLC-grade water for 3 minutes to remove residual ammonia. Finally, the separator is suspended in another preheated beaker of HPLC-grade water. In this beaker, the separator can be moved without exposing it to dust. Once the separator is ready for use, it is removed from the beaker and residual water droplets are blown out with particle-filtered dry nitrogen.

[0111] After cleaning, the assembly is performed as described below in a separately constructed "clean housing". In this housing, laminar air flow is ensured by using HEPA filters.

[0112] Before attaching the mirrors to the separator, they are also cleaned. To do this, each mirror is placed on a spin coater that spins the mirror at 8000 rpm. As the mirror spins, HPLC grade isopropyl alcohol is sprayed onto the mirror while wiping from the center to the edge with a lint-free cotton swab. Then, HPLC grade water is sprayed on the mirror to rinse off any isopropyl alcohol residue. When the substrate stops spinning, dry nitrogen is used to blow off any residual water droplets. The mirror is then placed in a mirror holder and the contact process begins, as described below.

[0113] To assemble the optical resonant cavity device 100, Figure 6 The mounting device 300 provides a contact stage that allows the mirror to be attached to the separator in a precisely controlled manner. The mounting device 300 includes a contact stage for the separator ( Figure 6 A bracket 310 (not shown) and a four-axis platform 320 holding the mirror to be contacted.

[0114] The bracket 310 is attached to a vertical translation stage, which itself is located on an optical track. This combination allows the spacer to be moved in the vertical direction over long distances with high precision. By moving the spacer upward, the surface facing the top surface approaches the first reflector to which it will be attached.

[0115] The mirror itself is held in a cylindrical mirror holder that only clamps the mirror lightly around all sides to prevent deformation of the mirror. The mirror holder is attached to a four-axis platform 320 that allows both horizontal movement of the mirror and tilting of the mirror along two axes relative to the spacer surface. Once the mirror is brought to its final position, a PTFE-tipped punch is used to release the mirror from the holder and push it onto the spacer where it is bonded together by direct optical contact.

[0116] On top of the tip-tilt stage 320, an interferometer and interferometer imaging system are set up to image the interference pattern between the front surface of the reflector and the top surface of the separator. By observing this interference pattern, the tip-tilt stage 320 is used to make the contact ring of the reflector parallel to the octagonal surface. This alignment process simulates the situation of the reflector in contact.

[0117] According to more details of interferometry, the alignment of the mirror to the separator is tested by interferometry, in particular, the mirror is centered to one of the separator holes and the mirror is ensured to be as parallel as possible to the separator carrier surface. A typical interference pattern has a bright area in the center, which is due to the direct reflection of the interferometer light from the mirror coating. This bright area is surrounded by a small dark ring, which represents the bevel on the separator hole. The bevel reflects the interferometer light out of the field of view of the interferometer imaging system, forming the dark ring. As a first alignment step, the mirror is roughly centered on the hole by centering the bright area on the dark ring.

[0118] A key feature of the interference pattern is its curved and straight edges. The curved edges are the result of interference between the carrier surface of the octagonal separator and the curved area of ​​the mirror. The straight edges are the result of interference between the carrier surface and the contact annulus of the mirror. These edges are made to disappear to ensure that the annulus is parallel to the carrier surface. For interferometer light at 633nm, a parallelism equivalent to a quarter edge can actually be achieved. This parallelism is equivalent to a relative angle of 1.4 arc seconds, which will result in a residual mode transfer of 69μm when R=10.2m. Therefore, for the final mirror, the contact process is repeated several times until the overlap of the final measurement is optimized.

[0119] The two plane mirrors are arranged by aligning their centers with the holes 33, 34 in the separator (see Figure 2) to optically contact the separator, which can be seen in the measured interference pattern as described above. For the first curved mirror, interference measurements ensure that it is centered and parallel to the separator surface. In this case, the first curved mirror is in optical contact with the separator. Subsequently, the octagonal separator is rotated 90° in its support seat 310 and the interference pattern is aligned again after the second curved mirror is installed. The laser is coupled into the cavity formed by the curved mirror and the facing flat mirror. The laser frequency is scanned and the cavity transmittance is measured by two photodetectors. In this way, it can be ensured that light is only coupled to the TEM of the two cavities. 00 To align the second curved mirror, a slit (or blade) mounted on another three-axis translation stage 330 is used to determine the position of the second cavity mold relative to the first cavity mold. This is done by moving the slit into the central hole 35 of the separator 30 (see Figure 2 ) and partially block the TEM with a slit 00 As a function of the slit position, the same TEM 00 The height of the mode-dependent transmission peak. The slit is centered on the mode position by maximizing the transmittance and ensuring that the modes overlap each other with zero or minimal displacement. Otherwise, the second curved mirror is translated horizontally while ensuring that it remains parallel to the octagonal separator surface until the modes overlap sufficiently. When the modes overlap, the second curved mirror is optically contacted using the method described above.

[0120] In more detail, once the second curved mirror is interferometrically aligned with the octagonal spacer, the laser is coupled into the cavity formed between the curved mirror and the already attached flat mirror. All these measurements use a laser at 689 nm, resulting in a mode diameter 2w0 = 791 μm according to equation (1). Preferably, it is coupled to the TEM with an efficiency of at least 95%. 00 modes to obtain usable transmittance data for the following steps. The laser frequency is scanned over multiple free spectrum ranges of the cavity, the transmittance is measured on a photodiode, and the resulting voltage trace is observed on an oscilloscope. The same is done for the second cavity that has been completed. As previously described, the overlap of the two cavity modes is determined by inserting a slit into the central hole 35 of the octagonal separator 30. The slit is machined into a stainless steel sheet. The sheet has two orthogonal slits with a width of 700 μm and a slit roughness of 20 μm. The short slit is used to determine the in-plane position where the projections of the two modes intersect. This position is determined by the position of the translation stage where the two modes are simultaneously maximally projected. Once this position is found, the long slit is used to determine the out-of-plane overlap of the two beams.

[0121] Representative results were obtained by plotting the transmittance of the two cavity modes versus the out-of-plane position of the translation stage, e.g. Figure 7 shown. Figure 7The results of a representative overlay measurement performed using a slit are shown. The laser frequency is swept as the slit is moved through the cavity. The transmission of each mode is highest when the slit is centered on the mode. The peaks can be fit with a parabola to determine the displacement of the mode. Therefore, a simple method to determine the residual out-of-plane displacement between cavity modes is to fit a parabola to each peak. In this case, this process results in a residual displacement of 16(5)μm or 2% of the mode diameter.

[0122] Due to the strict parallelism requirements of the separator, the mode displacement can be confirmed by taking an image of the transmitted laser beam as it exits the cavity, which directly shows the displacement of the mode relative to the mirrors and cavity aperture.

[0123] In separate measurements, the finesse of the cavity (and therefore the power enhancement) created by the cavity mirrors has been verified. For a multi-band reflective coating suitable for a particular experiment, it has been found that finesse above the specification for all wavelengths considered can be achieved. For the cases considered, a power amplification factor of 100-1000 is sufficient. By tuning the coating, the invention can be applied to any wavelength for which a high quality optical coating is available. For wavelengths of less interest, higher amplification factors can be easily obtained.

[0124] The features of the invention disclosed in the above description, the drawings and the claims can be of significance individually, in combination or in sub-combination for the realization of the invention in its different embodiments.

Claims

1. An optical resonant cavity device (100) having a cross cavity, the optical resonant cavity device (100) being used for optically trapping atoms, the optical resonant cavity device (100) comprising: - a first linear optical resonant cavity (10), which extends along a first resonant cavity optical path (12) between first resonant cavity reflectors (11A, 11B) and supports a first resonant cavity mode; - a second linear optical resonant cavity (20), which extends along a second resonant cavity optical path (22) between second resonant cavity mirrors (21A, 21B) and supports a second resonant cavity mode, wherein the first resonant cavity optical path (12) and the second resonant cavity optical path (22) cross the main resonant cavity plane; and - a carrier device, the carrier device carrying the first resonant cavity mirror (11A, 11B) and the second resonant cavity mirror (21A, 21B), wherein the first resonant cavity mirror (11) and the second resonant cavity mirror (21) are arranged so that the first resonant cavity mode and the second resonant cavity mode intersect each other to provide an optical lattice well (1) in the main resonant cavity plane; It is characterized in that - the carrier device comprises a monolithic separator (30) made of ultra-low expansion material and comprising a first carrier surface (31) accommodating the first resonant cavity mirror (11A, 11B) and a second carrier surface (32) accommodating the second resonant cavity mirror (21A, 21B), wherein - the first resonant cavity optical path (12) extends through a first separator hole (33) in the monolithic separator (30) between the first carrier surfaces (31), the second resonant cavity optical path (22) extends through a second separator hole (34) in the monolithic separator (30) between the second carrier surfaces (32), and The first separator hole (33) and the second separator hole (34) are hollow passages passing through the monolithic separator (30), the hollow passages being divided into two at their intersection.

2. The optical resonant cavity device according to claim 1, wherein The first resonator mirror (11A, 11B) and the second resonator mirror (21A, 21B) are respectively bonded to the first carrier surface (31) and the second carrier surface (32) in an adhesive-free manner.

3. The optical resonant cavity device according to claim 2, wherein The first resonator mirror (11A, 11B) and the second resonator mirror (21A, 21B) are optically bonded to the first carrier surface (31) and the second carrier surface (32), respectively.

4. An optical resonant cavity device according to any one of the preceding claims, wherein - the first resonant cavity reflector comprises a first curved reflector (11A); - the second resonant cavity reflector comprises a second curved reflector (21A), wherein - The first resonant cavity mirror (11A, 11B) and the second resonant cavity mirror (21A, 21B) are designed so that the first resonant cavity mode and the second resonant cavity mode comprise the lowest order Hermite-Gaussian mode of the first resonant cavity and the second resonant cavity, respectively.

5. The optical resonant cavity device according to claim 4, wherein - the first curved reflector (11A) and the second curved reflector (21A) have a selected radius of curvature, the selected radius of curvature making the optical lattice well have a size of 2*w0 in the plane of the main resonant cavity, the size being at least 300 μm, wherein, w0 is 1 / e of the first resonant cavity mode and the second resonant cavity mode 2 radius.

6. The optical resonant cavity device according to claim 4, wherein - the first curved reflector (11A) and the second curved reflector (21A) have a selected radius of curvature, the selected radius of curvature causing the optical lattice well to have a size of 2*w0 in the plane of the main resonant cavity, the size being at least 400 μm, wherein, w0 is 1 / e of the first resonant cavity mode and the second resonant cavity mode 2 radius.

7. The optical resonant cavity device according to claim 4 or 5, wherein - the first resonant cavity reflector comprises the first curved reflector (11A) and the first flat reflector (11B); -The second resonant cavity reflector includes the second curved reflector (21A) and a second flat reflector (21B).

8. The optical resonant cavity device according to claim 1, wherein - The monolithic separator (30) is made of ultra-low expansion glass or crystalline silicon.

9. The optical resonant cavity device according to claim 1, wherein - The first separator hole (33) and the second separator hole (34) are orthogonal to each other in the main resonant cavity plane.

10. The optical resonant cavity device according to claim 1, wherein The first separator hole (33) and the second separator hole (34) are arranged in a mirror-symmetrical manner with respect to a plane perpendicular to the main resonant cavity plane.

11. The optical resonant cavity device according to claim 1, wherein The monolithic separator (30) has a third separator hole (35) extending perpendicularly to the main resonant cavity plane and intersecting the first separator hole (33) and the second separator hole (34) at their intersection.

12. The optical resonant cavity device according to claim 11, further comprising: - Imaging means (40) arranged to image the optical lattice well along the third separator aperture (35).

13. The optical resonant cavity device according to claim 11, wherein - the third separator hole (35) is configured to accommodate a third optical path (36), the direction of the third optical path (36) deviating from the plane of the main resonant cavity, wherein - A retroreflector is arranged to generate a captured light field along said third optical path (36).

14. The optical resonant cavity device according to claim 1, wherein The monolithic separator (30) has at least one further separator hole (37) extending parallel to the plane of the main resonant cavity and intersecting the first separator hole (33) and the second separator hole (34) at their intersection.

15. The optical resonant cavity device of claim 14, wherein The one-piece separator (30) has two further separator holes, which are arranged symmetrically with respect to the arrangement of the first separator hole (33) and the second separator hole (34).

16. The optical resonant cavity device of claim 1, wherein - the monolithic separator (30) has an octagonal shape extending parallel to the plane of the main resonant cavity, wherein The first carrier surface (31) and the second carrier surface (32) are lateral side surfaces of the octagon.

17. The optical resonant cavity device of claim 1, wherein - The first resonant cavity mirror (11A, 11B) and the second resonant cavity mirror (21A, 21B) have a dielectric coating, which provides a reflectivity of at least 99%.

18. The optical resonant cavity device of claim 17, wherein - the dielectric coating is designed to provide a reflectivity of at least 99% for a plurality of resonant wavelengths of the first optical resonant cavity and the second optical resonant cavity.

19. The optical resonant cavity device of claim 1, wherein the optical resonant cavity device has at least one of the following metrics: - the size of the monolithic separator (30) in the plane of the main resonant cavity ranges from 3 cm to 20 cm; - the diameter of the first resonant cavity reflector (11A, 11B) and the second resonant cavity reflector (21A, 21B) ranges from 10 mm to 30 mm; - Each of the first resonant cavity reflector (11A, 11B) and the second resonant cavity reflector (21A, 21B) comprises a curved reflector having a radius of curvature ranging from 1 m to 20 m; The first resonant cavity reflector (11A, 11B) and the second resonant cavity reflector (21A, 21B) are arranged in an aligned manner so that the reflected laser beam in the first optical resonant cavity and the second optical resonant cavity deviates from the center of the hole by less than 25% of the diameter of the hole.

20. An atom trapping method for constructing a two-dimensional atomic arrangement, wherein the optical resonant cavity device (100) according to any one of the above claims is used, and the atom trapping method comprises the following steps: - constructing an optical lattice well (1) in a region where the first resonant cavity mode and the second resonant cavity mode intersect each other; - introducing an atomic cloud into the optical resonant cavity device (100); - Trapping said atoms in said optical lattice well (1).

21. The atom trapping method according to claim 20, wherein the step of constructing the optical lattice trap comprises: - coupling a first continuous wave (CW) laser beam and a second continuous wave (CW) laser beam into the first optical resonant cavity and the second optical resonant cavity, respectively; - overlapping the first resonant cavity mode and the second resonant cavity mode at the intersection of the first separator hole (33) and the second separator hole (34).

22. The atom trapping method according to claim 20, further comprising at least one of the following steps: - imaging the atoms trapped in the optical lattice trap (1) using an imaging device (40); - exciting and detecting transitions between energy states of the trapped atoms; - Exploiting the interactions between said atoms for the purposes of quantum simulation and / or quantum computing.

23. An atom trapping device (200) adapted to construct a two-dimensional arrangement of atoms, the atom trapping device (200) comprising: - An optical resonant cavity device (100) according to any one of claims 1 to 18; - a laser device (210, 220) adapted to couple a continuous wave laser beam into the first optical resonant cavity and the second optical resonant cavity; - an atom source and supply device (230), connected to the optical resonant cavity device; as well as - an imaging device (240) adapted to image the optical lattice well in the optical resonant cavity device.

24. The atom trapping device of claim 23, configured as an optical atomic clock.

25. The atom trapping device of claim 23, configured as a quantum simulation or quantum computing device.

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