High-temperature quantum sensor

Abstract

The vapor cell includes a cell body and a cell window anodized to the cell body. The cell window and the cell body define a vapor cavity configured to contain vapor containing multiple alkali atoms.

Description

TECHNICAL FIELD

[0001] This application claims the benefit of U.S. Provisional Patent Application No. 63 / 536,153 filed on September 1, 2023, the entire content of which is incorporated herein by reference.

[0002] GOVERNMENT RIGHTS The present invention was made with government support under Contract No. HR00112390115 awarded by the Defense Advanced Research Projects Agency (DARPA) of the Department of Defense. The Government holds certain rights in the present invention.

[0003] TECHNICAL FIELD The present disclosure relates generally to quantum sensors.

BACKGROUND ART

[0004] Quantum sensors utilize quantum phenomena such as superposition, entanglement, and quantum tunneling to measure physical quantities with extremely high precision. Quantum sensors can detect minute changes in environmental conditions including magnetic fields, electric fields, temperature, pressure, and gravitational fields. Quantum sensors may be used in atomic clocks, gyroscopes, magnetometers, interferometers, and other devices that accurately measure relatively small parameter changes such as time and acceleration. In some cases, quantum sensors use atomic spectroscopy and light-atom interactions to detect changes in the properties of gas-phase atoms to obtain accurate measurements of parameters acting on the gas-phase atoms. To dissociate alkali atoms into gas-phase atoms and maintain the thermal equilibrium of the gas-phase atoms, atomic sensors may operate at high temperatures, and may consume large amounts of power to maintain these high temperatures.

SUMMARY OF THE INVENTION

MEANS FOR SOLVING THE PROBLEMS

[0005] Generally, systems and technologies for quantum sensors capable of operating at high temperatures, for example, above 150 degrees Celsius (°C), or above approximately 150°C, are described. The quantum sensor includes a vapor cell configured to withstand high temperatures, for example, the mechanical viability of the vapor cell, and is configured to control the density of alkali atoms vaporizing within the vapor cell. In some examples, the quantum sensor includes a vapor cell containing a material that is nonreactive with alkali atoms and, for example, anodized for mechanical viability. In some examples, the quantum sensor includes a vapor cell containing an intermetallic alloy containing a metal and multiple alkali atoms, for example, to control the density of alkali atoms vaporizing within the vapor cell.

[0006] In one example, the present disclosure describes a vapor cell comprising a cell body and a cell window anodized to the cell body, wherein the cell window and the cell body define a vapor cavity configured to contain vapor containing a plurality of alkali atoms.

[0007] In another example, the present disclosure describes a sensor comprising a vapor cell, the vapor cell comprising a cell body, a cell window configured such that the cell window and the cell body define a vapor cavity and contain vapor comprising a plurality of alkali atoms, an intermetallic alloy comprising a metal and a plurality of alkali atoms, and a detector configured to receive probe light transmitted through the vapor cell.

[0008] In another example, the present disclosure describes a method for manufacturing a vapor cell, the method comprising arranging at least one of silicon or germanium on at least one of a cell window or a cell body, wherein the cell window and the cell body define a vapor cavity, and anodic bonding the cell window to the cell body via at least one of silicon or germanium.

[0009] Details of one or more examples of this disclosure are described in the accompanying drawings and the following description. Other features, purposes, and advantages of this disclosure will become apparent from the description and drawings, as well as from the claims. [Brief explanation of the drawing]

[0010] [Figure 1] Block diagram shows an exemplary detection system using the techniques of the present disclosure. [Figure 2A] This is a cross-sectional view of an exemplary vapor cell for a quantum sensor according to the technology of this disclosure. [Figure 2B] Figure 2A shows a cross-sectional view of an exemplary vapor cell in a quantum sensor with a different configuration, according to the technology of this disclosure. [Figure 3] This is a cross-sectional view of another exemplary vapor cell of a quantum sensor according to the technology of the present disclosure. [Figure 4] This is a flowchart illustrating an exemplary method for manufacturing a steam cell using the technology of this disclosure. [Modes for carrying out the invention]

[0011] Generally, systems and technologies of quantum sensors capable of operating at high temperatures, for example, above approximately 150 degrees Celsius (°C), are described. In some examples, quantum sensors can operate at temperatures above 500°C, for example, above approximately 500°C. Quantum sensors may include magnetometers (scalar or vector), atomic clocks, Rydberg electromagnetic (EM) radiation sensors (e.g., EM waves and / or EM energy), or any suitable quantum sensor.

[0012] Conventional quantum sensors can degrade at substantially high temperatures. For example, fluxgate magnetic sensors can be affected by the breakdown of the magnetic wire insulating coating at high temperatures, issues related to differences in the thermal expansion coefficients (CTEs) of components, and temperature influences on microcircuits closely attached to the fluxgate sensor. The operation of a typical vapor cell magnetometer involves alkali atoms maintained at relatively low temperatures, such as below about 100°C. At higher temperatures, the alkali atoms used to detect the magnetic field react with the walls of the vapor cell, which are usually made of borosilicate glass, depleting the alkali atoms and "darkening" the cell, for example, reducing the transmission of query light, such as excitation and / or probe laser light. In other words, the material of the vapor cell can react with vaporized alkali atoms, and the inner surface of the vapor cell can become substantially opaque to excitation and / or probe radiation (e.g., light), in addition to reduced light transmission and / or depletion of the alkali atom vapor, reducing the sensing capability of the quantum sensor.

[0013] The amount of alkali atoms in a vapor cell may need to be carefully controlled. For example, changes in alkali atom density can cause pressure fluctuations within the vapor cell or increase collisions between alkali atoms and buffer gas. Typically, a vapor cell may operate at a constant temperature using a droplet storage unit for alkali atoms within the cell, which functions to balance the loss of alkali atoms to an atomic sink (e.g., reactions with other materials such as the cell body, cell window, or other materials) and maintain a substantially constant density of vaporized alkali atoms. Such a configuration cannot be used over a wide range of temperatures because the optical density of the vapor can change considerably, and the density can increase to the point where the vapor itself becomes substantially opaque for probing light and / or excitation (e.g., "pump") radiation.

[0014] According to the technologies, systems, devices, and / or sensors disclosed herein, a quantum sensor includes a vapor cell configured to withstand high temperatures, for example, the mechanical viability of a vapor cell, and configured to control the density of alkali atoms vaporized within the vapor cell. The alkali atoms or vaporized alkali atoms may be lithium, sodium, potassium, rubidium, cesium, or any suitable alkali. In some examples, the quantum sensor includes a vapor cell comprising a material that is inactive with alkali atoms and, for example, an anode-bonded material for mechanical viability. For example, the vapor cell may include a cell body comprising a material that is inactive with alkali atoms or alkali vapor (e.g., does not react or chemically react), such as sapphire, titanium, germanium, or any material that is inactive with vaporized alkali atoms.

[0015] The vapor cell may also include a cell window for probing the contents of the vapor cell. The cell window is configured to form a seal with the cell body to hold a vapor containing multiple alkali atoms within a volume defined by the cell body and the cell window (e.g., the cell volume), for example, the cell body may be substantially hollow and open at opposite ends, sealed at both ends through the cell window. For example, the cell window may include a material that is inactive with alkali atoms, such as sapphire, titanium, or germanium, or any material that is inactive with vaporized alkali atoms and configured to be anode-bonded to the cell body. The window may also be substantially optically transparent to at least certain optical frequencies, such as excitation radiation and probe light. For example, the vapor cell may include a sapphire cell window made of amorphous silicon anode-bonded to a sapphire cell body.

[0016] Rather than using a homogeneous source of alkali atoms, the vapor cells described herein may include a heterogeneous source of alkali atoms chemically configured to slow down and release alkali atoms at high temperatures. The vapor cell may include an intermetallic alloy containing a metal and multiple alkali atoms. The intermetallic alloy may be configured for temperature-independent control of the density of vaporized alkali atoms in the vapor cell. In some examples, the intermetallic alloy may be configured to hold the alkali atoms at substantially high temperatures, e.g., above about 150°C, so as not to increase the density of vaporized alkali atoms so as not to further vaporize the alkali atoms. For example, a vapor cell may be sealed with an intermetallic alloy within the cell and heated to a first high temperature, which may be above the phase transition temperature of the intermetallic alloy. The first temperature may be significantly higher than the operating temperature of the vapor cell, e.g., above 500°C, at which point alkali atoms may vaporize from the intermetallic alloy. The intermetallic alloy may be heated to the first temperature over a first time configured to yield a vapor of alkali atoms having a particular desired density. The intermetallic alloy can then be cooled or allowed to cool, and the vapor cell can maintain a relatively constant density of vaporized alkali atoms as a function of temperature, even at temperatures above 150°C. For example, the intermetallic alloy may include alkali-gold alloys that may have a melting point of 495°C, 490°C, or about 500°C. The alkali-gold alloy can be heated above its melting point while monitoring the absorption of the probe beam (by the vaporized alkali atoms) to release alkali atoms of a known density into vapor.

[0017] The sensors and technologies described herein may provide quantum sensors having improved temperature stability and an extended operating temperature range. The sensors and technologies described herein may provide improved control of the density of vaporized alkali atoms in a vapor cell and the ability to change the density of alkali atoms in the vapor cell by, for example, heating an intermetallic alloy that is included. For example, a quantum sensor using an intermetallic alloy, a controllable source, and an inert or non-reactive material in the vapor cell body and window to eliminate an alkali sink, can control the number and / or density of alkali atoms to be substantially constant over a wide temperature range, including temperatures above 150°C. The sensor may include a vapor cell that improves sensitivity at normal or relatively high (e.g., above 150°C) temperatures. For example, a vapor cell may prevent and / or reduce blackening of the vapor cell by, for example, the deposition of material such as alkali atoms on the cell window and / or by increasing the density of vaporized alkali atoms to increase the optical density of the cell in order to probe light and / or excitation radiation that degrades the sensor signal, signal intensity, or signal-to-noise ratio. The sensors and technologies described herein may provide improved sensor viability. For example, the vapor cells disclosed herein may provide improved viability of window bonding and / or sealing to the cell body (e.g., via anodic bonding and / or sealing such as bonding and / or sealing between sapphires) at relatively high temperatures, such as above 150°C, above 500°C, or any suitable relatively high temperature, by reducing bonding / seal degradation, leakage, and material intrusion into the vapor cell.

[0018] Figure 1 is a block diagram illustrating an exemplary quantum sensing system 100 according to the technology of the present disclosure. In the illustrated example, the quantum sensing system 100 includes a sensor 112 and a computing device 106. The sensor 112 includes a vapor cell 102, a detection system 104, and a preparation system 108. Although the sensor 112 is described herein as a magnetometer, the quantum sensing system 100 and / or the sensor 112 may be configured to detect a magnetic field, incident EM radiation, and / or any other suitable stimulus.

[0019] The vapor cell 102 may contain vapor of atoms suitable for probing and measuring optical and magnetic properties, such as alkali atoms, due to their well-defined electronic structures and the precision with which their resonance frequencies and energy levels can be manipulated and detected. In some examples, the vapor cell 102 may be configured to be a transducer for converting the physical phenomenon 110 into electrical information via the detection system 104. The physical phenomenon 110 is described below as the magnetic field 110 for the sake of brevity, but may include a magnetic field (e.g., strength, direction, and / or relative change of the magnetic field), incident EM radiation (e.g., EM energy, light waves, radio waves, etc.), or other physical phenomena. For example, the vapor cell 102 may convert at least part of the energy of the scalar or vector magnetic field 110 and / or EM radiation 110 (e.g., having a frequency in a first frequency range such as MHz, THz, or GHz radio waves) into a signal that may be an optical signal detectable by a photodiode (e.g., EM radiation having a frequency in a second range such as infrared or visible light), or an ionization state of atoms in the vapor cell, or any suitable detectable signal.

[0020] The detection system 104 may include one or more detectors, circuits, meters, etc. configured to detect the response of the alkali atoms to the magnetic field 110 after the alkali atoms are prepared via the preparation system 108, for example after a plurality of alkali atoms are prepared to be in the Rydberg state. For example, the detection system 104 may include an optical detector configured to detect the amount of probe light from the preparation system 108 that passes through the vapor cell 102, and capture the absorption spectrum of the alkali atoms as a function of the detuning of the frequency of the probe light and the indication / quantification of electromagnetically induced transparency (EIT) of the alkali atom vapor. The detection system 104 may be configured to detect the response of the alkali atoms to the magnetic field 110 when prepared in the Rydberg state, and convert the detected response into one or more signals, such as analog signals and / or digital signals.

[0021] Computing device 106 may be configured to receive analog signals and / or digital signals from detection system 104. For example, computing device 106 may be configured to process, record and / or store signals received from detection system 104, and may be configured to store and / or output raw data and / or processed data indicative of incident EM radiation 110, for example the quantity and / or spectral components of EM radiation 110. Computing device 106 may include one or more processors, memory, and interface components.

[0022] For example, the one or more processors of computing device 106 may include any one or more of processing circuitry, a microprocessor, a controller, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or equivalent discrete or integrated logic circuitry. The functions attributed to the processors described in this specification may be provided, for example, by processing circuitry of a hardware device supported by software and / or firmware.

[0023] In some examples, the memory of computing device 106 may include any volatile or non-volatile media such as random access memory (RAM), read-only memory (ROM), non-volatile RAM (NVRAM), electrically erasable programmable ROM (EEPROM), flash memory, and the like. The memory may be a storage device or other non-transitory medium, and may be used by processing circuitry to store information related to sensing system 100, such as information related to vapor cell 102, detection system 104, preparation system 108, and incident EM radiation 110. In some examples, the memory may store information or data previously received from detection system 104 for later retrieval. In some examples, the memory may store settings, determined values, and / or calculated values for later retrieval.

[0024] In some examples, the interface components of computing device 106 may include output devices such as a display, sound card, video graphics adapter card, speaker, presence-sensitive screen, one or more USB interfaces, video and / or audio output interfaces, or any other type of device capable of generating haptic, audio, video, or other output. Display devices may use technologies including liquid crystal displays (LCDs), quantum dot displays, dot matrix displays, light-emitting diode (LED) displays, organic light-emitting diode (OLED) displays, cathode ray tube (CRT) displays, e-ink, or any other type of display capable of generating monochrome, color, or haptic, audio, and / or visual output.

[0025] In some examples, the computing device 106 may be integrated with the detection system 100, or with one or more of the following: the steam cell 102, the detection system 104, and the preparation system 108. In other examples, the computing device 106 may be separate from external devices, such as the detection system 100, and configured to communicate with the detection system 100.

[0026] The preparation system 108 may be configured to emit one or more EM radiation frequencies that can be used to prepare alkali atoms in the vapor cell 102 from a first quantum energy state, which may be the ground state of the alkali atom vapor, to a second higher quantum energy state, such as a Rydberg state. In some examples, the preparation system 108 may include any hardware suitable for preparing atoms to the Rydberg state. For example, the preparation system 108 may include multiple EM radiation sources and physical / optical elements configured to guide the EM radiation from one or more EM radiation sources. In some examples, the preparation system 108 may be all-optical, including, for example, EM radiation sources, and may include light sources such as lasers, light-emitting diodes, incandescent sources, and fluorescent sources. The physical / optical elements may include lenses, mirrors, diffraction gratings, windows, filters, waveguides, fibers, or any physical / optical elements for guiding and / or shaping (e.g., beam shaping) the EM radiation from the radiation sources to incident on the alkali atoms in the vapor cell 102.

[0027] In some examples, the preparation system 108 may be configured to emit a plurality of EM radiation frequencies configured to be incident on alkali atoms in the vapor cell 102. For example, the preparation system 108 may be configured to emit a plurality of EM radiation "beams" each having one or more frequencies (e.g., wavelengths) directed into the vapor cell 102. In some examples, the preparation system 108 may include three EM frequencies (e.g., a "three-photon" system) configured to excite alkali atoms into a Rydberg state. In some examples, the preparation system 108 may include more or fewer than three EM radiation frequencies, e.g., one EM radiation frequency, two EM radiation frequencies, or four or more EM radiation frequencies. In some examples, the plurality of EM radiation frequencies of the preparation system 108 may be configured to prepare alkali atoms in the vapor cell 102 to a Rydberg state via one or more intermediate quantum energy states.

[0028] The vapor cell 102 may include a cell body and one or more cell windows anodized to the cell body. The cell body and cell windows may define the volume of a vapor cavity, for example, within the vapor cell 102, and the vapor cell 102 may be configured to contain, for example, vapor containing a plurality of alkali atoms within the vapor cavity. The anodized joint between the cell body and the cell window may form an hermetically sealed seal, which may allow the vapor cell 102 to have a relatively low or zero vapor permeability, for example, low or zero alkali vapor loss and / or vapor ingress or leakage into or out of the vapor cell 102, for example, low or zero ingress of water, oxygen or helium. In some examples, the cell body and cell windows may have substantially the same CTE, for example, a matched CTE, and the anodized joint may also have a CTE substantially matched to that of the cell body and / or cell window.

[0029] Figures 2A and 2B are cross-sectional views of an exemplary vapor cell 202 of a quantum sensor according to the art of the present disclosure. Figure 2A shows the vapor cell 202 and a probe light 208A and excitation radiation 208B in a first configuration, and Figure 2B shows the probe light 208A and excitation radiation 208B in a second configuration. The vapor cell 202 may be substantially similar to the vapor cell 102 described above.

[0030] In the example shown, the vapor cell 202 includes a cell body 204, a cell window 206a, and a cell window 206b on the opposite side of the cell body 204 from cell window 206a. The cell body 204 may contain sapphire or germanium. The cell windows 206a and 206b may be anode-bonded to the cell body 204 via anode junctions 222a and 222b, respectively. The cell windows 206a and 206b (collectively, "cell window 206") may contain sapphire and may have high light transmittance to probe light 208A and / or excitation radiation 208B; for example, the cell window 206 may be substantially optically transparent to probe light 208A and / or excitation radiation 208B. The cell body 204 and the cell windows 206 may define a vapor cell cavity 212 and may be configured to contain a vapor containing a plurality of alkali atoms within the vapor cell cavity 212.

[0031] The probe light 208A may be EM radiation having a radio frequency or optical frequency detectable via the detection system 104. The probe light 208A and the excitation radiation 208B may be configured to propagate to and / or through the vapor cell cavity 212 and / or through multiple alkali atoms, for example. In the example of Figure 2A, both the probe light 208A and the excitation radiation 208B are configured to propagate to and / or through the vapor cell cavity 212 via a vapor cell window, for example 206a, and at least a portion of the probe light 208A (for example, a portion not absorbed by alkali vapor) is configured to propagate from the vapor cell cavity 212 via the cell window 206b for detection by, for example, the detection system 104. That is, in Figure 2A, the probe light 208A and the excitation radiation 208B propagate in the same direction. In the example shown in Figure 2B, probe light 208A and 208B are configured to propagate in different directions through the vapor cell cavity 212 and / or through the vapor cell cavity 208. For example, the cell body 204 may also be substantially transparent to at least one of the excitation radiation 208B or probe light 208A, as shown in the example.

[0032] The probe light 208A and excitation radiation 208B may have frequencies capable of exciting at least some of the alkali atoms in the vapor cell cavity 212 to excited quantum states such as the Rydberg state. For example, the probe light 208A may be infrared, visible, or ultraviolet laser light, such as 780 nanometer (nm) laser light. The excitation radiation 208B may be electromagnetic radiation (EM) having a radio frequency or optical frequency, such as 480 nm laser light. A portion of the probe light 208A can excite some of the alkali atoms in the vapor cell 202 to a first quantum state, and the excitation radiation 208B can excite some of the alkali atoms to a second Rydberg quantum state. The quantum states of alkali atoms excited to the Rydberg state may be perturbed, for example, by a magnetic field, radio waves, or other physical phenomena, and may be sensitive to them, so that the alkali atoms may be "detuned" from the Rydberg state, thereby changing the amplitude of the probe light 208A propagating through the vapor cell 202 to the detection system 104. In some examples, the excitation radiation 208B may include multiple radiation frequencies (e.g., from multiple radiation sources) configured to excite alkali atoms to a Rydberg state via one or more intermediate quantum states, together with the probe light 208A. For example, the excitation radiation 208B may include 776 nanometer (nm) laser light and 1260 nanometer laser light.

[0033] The vapor cell 202 is configured to maintain a proportion and / or amount of alkali atoms excited to a Rydberg state to detect external EM radiation such as magnetic fields or radio waves, even at relatively high temperatures, e.g., above about 150°C, or above about 250°C, or above about 490°C, or above about 495°C, or even at any suitable high temperature (e.g., rising from room temperature). For example, the vapor cell 202 may be configured to maintain a sealed state at temperatures above about 150°C, or above about 250°C, or above about 495°C, and to maintain a density of multiple alkali atoms in the vapor cell cavity 212 that is substantially constant as a function of temperature at the temperature of the vapor cell 202 above about 150°C, or above about 250°C, or above about 490°C, or above about 495°C, and to prevent vaporized alkali atoms from reacting with the cell body 204 and / or cell window 206 at temperatures above about 150°C, or above about 250°C, or above about 490°C, or above about 495°C.

[0034] For example, the vapor cell 202 includes an anode junction 222a and an anode junction 222b (collectively, “anode junction 222”), and the anode junctions 222a and 222b can maintain an hermetically sealed bond between the cell body 204 and the cell window 206. The anode junction 222 may include silicon, germanium, and / or glass. In the illustrated example, the anode junction 222a includes three layers, namely two layers 218a and 220a of amorphous silicon adjacent to opposing faces of glass 216a, and similarly, the anode junction 222b includes three layers, namely two layers 218b and 220b of amorphous silicon adjacent to opposing faces of glass 216b. In some examples, layers 218a and 218b (collectively "layer 218") may be silicon or germanium and may be located on the inner surface of the cell window 206, on the surface of the glass 216a, or both. Similarly, layers 220a and 220b (collectively "silicon 220") may be silicon or germanium and may be located on the surface of the glass 216b, on the surface of the cell body 204, or both. In some examples, the anode junction 222 may have a thickness of about 10 micrometers or less in the x-direction (e.g., a thickness of 348 as shown in Figure 3), as illustrated. For example, the glass 216a and / or 216b may have a thickness of less than 10 micrometers, and layers 218a, 218b, 220a, and 220b may each have a thickness of about 200 nanometers or less. Although shown as three layers, the anode junction 222 may contain more or fewer layers. For example, the anode junction 222 may include a single layer 218 (or 220) of amorphous silicon or germanium between the cell window 206 and the cell body 204.

[0035] The vapor cell 202 may be inert at high temperatures, such as above about 150°C, or above about 250°C, or above about 490°C, or above about 495°C, in the presence of alkali metals. For example, the cell body 204 and the cell window 206 may be sapphire, which remains substantially transparent to probe light 208A and / or excitation radiation 208B, does not act as a sink for vaporized alkali atoms, and does not react with alkali atoms, for example, so that atoms deposit on the inner surface of the cell body 204 and / or the cell window 206. The cell window 206, the cell body 204, and / or the anode junction 222 may have a CTE greater than about 6 parts per million (ppm / °C). For example, the cell window 206 may have a CTE substantially consistent with that of the cell body 204 and / or the anode junction 222. Glass 216a and glass 216b may include D-263 Schott glass, BK-7 optical glass, soda-lime glass, or any suitable glass having a CTE greater than approximately 6 ppm / °C. The vapor cell 202 may be made of materials such as those listed in Table 1 below. In some examples, the vapor cell 202 may contain silicon having a CTE of less than approximately 6 ppm / °C, however the amount of silicon (e.g., thin layer) for the anodic bonding may be such that the CTE of the silicon does not substantially contribute to the difference in thermal expansion or contraction, for example, the silicon may have a small mass that does not negate the CTE match of the materials for the vapor cell 202.

[0036] [Table 1]

[0037] In general, the vapor cell 202 may contain materials capable of withstanding a considerable temperature range, and may be assembled using materials and methods capable of withstanding a considerable temperature range. For example, optical components for alkali atom preparation and signal readout may be made of high-quality quartz and fused silica and bonded in place with high-temperature ceramic adhesive.

[0038] Figure 3 is a cross-sectional view of an exemplary vapor cell 302 of a quantum sensor according to the art of the present disclosure. The vapor cell 302 may be substantially the same as the vapor cell 102 of Figure 1 and the vapor cell 102 of Figures 2A and 2B, except for the differences described herein. In the illustrated example, the vapor cell 302 includes an alkali source 330 formed from an intermetallic alloy and a thermal control element 332.

[0039] The alkali source 330 may include a metal and an alkali, for example, an intermetallic alloy containing multiple alkali atoms. For example, the alkali source 330 may include gold and / or silver and rubidium. The alkali source 330 may have a relatively high decomposition temperature, for example, above about 150°C, or above about 250°C, or above about 490°C, or above about 495°C. Above the decomposition temperature, alkali atoms may be released from the alkali source 330 and vaporized. In some examples, the alkali source 330 may be heated so that alkali atoms of a desired density are released from the alkali source 330 and vaporized. In some examples, the alkali source 330 may have a decomposition temperature considerably higher than the operating temperature of the vapor cell 302. For example, the alkali source 330 may have a decomposition temperature of approximately 495°C and may be heated to a temperature of 495°C or higher over a period of time (or over a period of time according to a temperature profile as a function of time) to release alkali atoms from the alkali source 330 so that a specific desired density of vaporized alkali atoms is achieved within the vapor cell cavity 212. Subsequently, during use, the vapor cell 302 is operated at a relatively high temperature, e.g., above approximately 150°C, but below the decomposition temperature of the alkali source 330 (e.g., below approximately 495°C), thereby maintaining the density of vaporized alkali atoms within the vapor cell 302 even at relatively high temperatures. If the density of vaporized alkali atoms within the vapor cell 302 changes over time, the desired density may be achieved again, for example, via the alkali source 330, which may function as a source or sink of alkali atoms to maintain the density of vaporized alkali atoms. For example, the alkali source 330 may be heated to a temperature above its decomposition temperature in order to increase the density of vaporized alkali atoms, or the temperature of the alkali source 330 may be controlled to decrease the density of vaporized alkali atoms in the vapor cell cavity 212.

[0040] In the illustrated example, the alkali source 330 is placed on the inner surface of the cell body 204. In other examples, the alkali source 330 may be of any form and may be located anywhere within the steam cell cavity 212. For example, the alkali source 330 may be a pellet placed within the steam cell cavity 212.

[0041] In the illustrated example, the steam cell 302 includes a thermal control element 332. The thermal control element 332 may be configured to heat and / or cool the alkali source 330 within the steam cell cavity 212. For example, the thermal control element 332 may include a heater and / or heating element configured to heat the alkali source 330 to at least the alloy decomposition temperature. In the illustrated example, the thermal control element 332 is a platinum heater formed as a coil within the steam cell body 204 and positioned sufficiently close to the alkali source 330 to heat or cool the alkali source 330. In other examples, the thermal control element 332 may be located on the inner surface of the cell body 204 or on the outer surface of the cell body 204. In some examples, the steam cell 302 may not include a thermal control element 332 and may be configured so that the alkali source 330 can be thermally controlled. For example, the steam cell 302 may be substantially transparent to radiation that can be induced onto the alkali source 330 to change the temperature of the alkali source 330, or the steam cell 302 may be configured so that the alkali source 330 can be inductively heated, for example, via an induction coil. In some examples, the thermal control element 332 may function as an induction coil.

[0042] In the example shown, the steam cell 302 may be substantially cylindrical with a circular cross-section. The steam cell 302 may have, for example, a diameter 340, a cell body thickness 342, and a steam cavity diameter 344 along the y-direction in the example shown. In some examples, the diameter 340 may be about 3 millimeters (mm), or about 5 mm, or about 7 mm, or about 10 mm, or any suitable diameter. The cell body thickness 342 may be about 0.5 mm, or about 1 mm, or about 3 mm, or about 5 mm, or any suitable thickness. The steam cavity diameter 344 may be about 2 mm, or about 5 mm, or about 7 mm, or any suitable diameter. The cell window 206 may have a thickness of about 0.1 mm, or about 0.5 mm, or about 1 mm, or any suitable thickness (along the x-direction, for example, as shown). The steam cell 302 may have an overall length 350 of approximately 2 mm, or approximately 5 mm, or approximately 10 mm (for example, along the x-direction as shown), or any suitable overall length.

[0043] The vapor cell 302 may have a source and sink for vaporized alkali atoms removed over operating conditions, and the number and / or density of vaporized alkali atoms in the vapor cell cavity 212 may remain substantially constant, for example, as a function of temperature. In some examples, the vapor cell 302 may include glass layers 216a and 216b of the anode junctions 222a and 222b, which may be sinks for vaporized alkali atoms, but the diffusion of alkali atoms into the glass layers 216a and 216b from the cell is 10 10 Less than 10000 alkali atoms (e.g., less than 1 picogram of rubidium atoms) can be removed, and the diffusion rate of alkali atoms can be exponentially reduced until the sink is effectively saturated. Since the glass layers 216a and 216b are not in the optical access area (e.g., probe light 208A and / or excitation radiation 208B do not propagate to or through the glass layers 216a and 216b), any darkening of the glass layers 216a and 216b related to this diffusion does not affect the sensor signal using the vapor cell 302.

[0044] The vapor cell 302 may be configured such that the density of alkali atoms in the vapor cell cavity 212 is substantially constant as a function of temperature via the alkali source 330. For example, the number density of alkali atoms is 1.927 × 10⁻⁶ -7 Amagat (AMG), or in other words, 5.178 × 10 18 atoms / m 3This can correspond to the equilibrium amount of alkali atoms at 100°C. Using the density of gold as the metal, if the alkali source 330 is completely depleted, it will use an alloy volume of 0.175 cubic micrometers to fill a 1 cc vapor cell cavity 212. By depleting only 1% of the alkali source 330, the volume of the alkali source 330 will only increase to 17.5 cubic micrometers to fill a 1 cc vapor cell. The alkali source 330 can be deposited in such a way that it does not affect the transparent opening and sensors (e.g., magnetometer) of the vapor cell 302 during operation. For example, in the case of rubidium, the temperature of the alkali source 330 can be raised about 25°C higher than the melting point of the alkali source 330 before it re-solidifies in order to release 1% of the alkali atoms, allowing for significant control of the final number density of alkali atoms in the vapor cell 302. In some cases, the emission of alkali atoms from alkali source 330 can also be monitored in situ using Doppler-free saturated absorption spectroscopy to ensure the exact number density in vapor cell 302 before operation.

[0045] Figure 4 is a flowchart of an exemplary method for manufacturing a steam cell according to the technology of this disclosure. This method will be described with reference to the detection system 100 and steam cell 102 of Figure 1 and the steam cells 202 and 302 of Figures 2A to 3, but the method discussed herein may include and / or utilize other systems and methods in other examples.

[0046] The manufacturer may place at least one of silicon or germanium 218, 220 on at least one of the cell window 206 or the cell body 204 (402). For example, the manufacturer may place the silicon or germanium layers 218, 220 directly on the surface of the cell window 206 or the cell body 204, or by coating, sputtering, depositing, or vapor deposition (e.g., by atomic layer deposition) on the glass layer 216. In some examples, the manufacturer may place glass on, for example, the silicon or germanium layers 218, 220 already placed on the surface of the cell window 206 or the cell body 204.

[0047] The manufacturer may anode-bond the cell window 206 to the cell body 204 via at least one of silicon or germanium 218, 220 (404). For example, the manufacturer may compress the silicon or germanium layers 218, 220 and optionally the glass layer 216 between the cell window 206 and the cell body 204 while heating the cell window 206 or the cell body 204 and / or applying a voltage or current to the silicon or germanium layers 218, 220 to form an anode junction 222.

[0048] In some examples, the manufacturer may heat the alkali source 330 in the vapor cell cavity 212 to the alloy decomposition temperature to release at least some of the alkali atoms from the alloy as vapor in the vapor cell cavity 212. The manufacturer may heat the alkali source 330 before anodizing the cell window 206 to the cell body 204, for example, in a vacuum or inert gas environment where the alkali source 330 may be inside or outside the vapor cell cavity 212 but configured to vaporize the alkali atoms into the vapor cell cavity 212, or the manufacturer may heat the alkali source 330 after anodizing the cell window 206 to the cell body 204.

[0049] The following examples may illustrate one or more aspects of this disclosure.

[0050] Example 1: The vapor cell includes a cell body and a cell window anodized to the cell body, wherein the cell window and the cell body define a vapor cavity configured to contain vapor containing multiple alkali atoms.

[0051] Example 2: The vapor cell of Example 1, in which the cell window is substantially optically transparent to probe light.

[0052] Example 3: A vapor cell of Example 1 or Example 2, wherein the cell window contains sapphire and the cell window has a coefficient of thermal expansion (CTE) greater than approximately 6 parts per million degrees Celsius (ppm / °C).

[0053] Example 4: A vapor cell according to any one of Examples 1 to 3, wherein the anode junction contains at least one of silicon or germanium, and the cell body contains at least one of silicon or germanium.

[0054] Example 5: A steam cell from any of Examples 1-4, wherein the cell body and cell window are nonreactive with multiple alkali atoms at a steam cell temperature exceeding approximately 150 degrees Celsius (°C).

[0055] Example 6: A steam cell configured to maintain a density of multiple alkali atoms within a steam cavity that is substantially constant as a function of temperature for steam cell temperatures above approximately 150°C, one of the steam cells from Examples 1 to 5.

[0056] Example 7: A vapor cell from any one of Examples 1 to 6, further comprising an intermetallic alloy containing a metal and multiple alkali atoms.

[0057] Example 8: The vapor cell of Example 7, wherein the metal contains at least one of gold or silver.

[0058] Example 9: The intermetallic alloy is a vapor cell of Example 7 or Example 8, having an alloy decomposition temperature of approximately 150°C or higher.

[0059] Example 10: A steam cell from any one of Examples 7-9, further comprising a heater configured to heat an intermetallic alloy to at least its alloy decomposition temperature.

[0060] Example 11: The sensor includes a vapor cell, the vapor cell including a cell body, a cell window configured such that the cell window and the cell body define a vapor cavity and contain vapor containing a plurality of alkali atoms, an intermetallic alloy containing a metal and a plurality of alkali atoms, and a detector configured to receive probe light transmitted through the vapor cell.

[0061] Example 12: The sensor from Example 11, where the cell window is substantially optically transparent to probe light.

[0062] Example 13: The sensor of Example 11 or Example 12, wherein the cell window contains sapphire and the cell window has a coefficient of thermal expansion (CTE) greater than approximately 6 parts per million degrees Celsius (ppm / °C).

[0063] Example 14: A sensor described in any one of Examples 11-13, in which the cell window is anode-bonded to the cell body.

[0064] Example 15: The sensor according to Example 14, wherein the cell body comprises at least one of sapphire or germanium, and the anode junction comprises at least one of silicon or germanium.

[0065] Example 16: A sensor according to any one of Examples 11-15, wherein the cell body and cell window are nonreactive with multiple alkali atoms at a vapor cell temperature exceeding approximately 150 degrees Celsius (°C).

[0066] Example 17: A steam cell is configured to maintain a density of multiple alkali atoms within a steam cavity that is substantially constant as a function of temperature for steam cell temperatures above approximately 150°C, using one of the sensors from Examples 11–16.

[0067] Example 18: The sensor according to any one of Examples 11-17, wherein the metal comprises at least one of gold or silver.

[0068] Example 19: An intermetallic alloy having a decomposition temperature above approximately 150°C, as described in any one of Examples 11-18.

[0069] Example 20: The sensor according to any one of Examples 11-19, further comprising a heater configured to heat the alloy to at least the alloy decomposition temperature.

[0070] Example 21: A method for manufacturing a vapor cell, comprising: arranging at least one of silicon or germanium on at least one of a cell window or a cell body, wherein the cell window and the cell body define a vapor cavity; and anodic bonding the cell window to the cell body via at least one of silicon or germanium.

[0071] Example 22: The method of Example 21, further comprising placing glass on at least one of silicon, germanium, a cell window, or a cell body, and anodic bonding the cell window to the cell body via the glass.

[0072] Example 23: The method of Example 21 or Example 22, further comprising heating an intermetallic alloy containing a metal and a plurality of alkali atoms to an alloy decomposition temperature in a vapor cavity, thereby releasing at least a portion of the plurality of alkali atoms from the alloy as vapor in the vapor cavity.

[0073] Example 24: A vapor cell comprising a cell body, a cell window having a coefficient of thermal expansion (CTE) greater than approximately 6 parts per million degrees Celsius (ppm / °C), the cell window being anodically bonded to the cell body, the cell window and cell body being configured to define a vapor cavity and contain vapor containing a plurality of alkali atoms, the anodizing junction containing at least one of silicon or germanium, the cell body and cell window being nonreactive with the plurality of alkali atoms at a vapor cell temperature exceeding approximately 150 degrees Celsius (°C), and an intermetallic alloy containing a metal and a plurality of alkali atoms, having an alloy decomposition temperature exceeding approximately 490°C.

[0074] The technologies described herein can be implemented, at least in part, in hardware, software, firmware, or any combination thereof. For example, various aspects of the technologies may be implemented in one or more microprocessors, DSPs, ASICs, FPGAs, or other equivalent integrated or discrete logic QRS circuits, or in any combination of such components, embodied in an external device. The terms “processor” and “processing circuit” may generally refer to any of the aforementioned logic circuits alone or in combination with other logic circuits, or to any other equivalent circuit alone or in combination with other digital or analog circuits.

[0075] In software implementations, at least some of the functions resulting from the systems and devices described herein may be embodied as details on a computer-readable storage medium such as RAM, DRAM, SRAM, magnetic disks, optical disks, flash memory, or EPROM or EEPROM. Instructions may be executed to support one or more of the functions described herein.

[0076] In addition, in several respects, the functions described herein may be provided within dedicated hardware and / or software modules. The descriptions of different characteristics of modules or units are intended to highlight different functional aspects and do not necessarily imply that such modules or units must be implemented by separate hardware or software components. Rather, the functions associated with one or more modules or units may be performed by separate hardware or software components, or integrated within common or separate hardware or software components. Furthermore, this technique may be fully implemented in one or more circuits or logic elements.

Claims

1. It is a steam cell, The cell body and The cell body includes a cell window anode-bonded to the cell body, wherein the cell window and the cell body define a vapor cavity configured to contain vapor containing a plurality of alkali atoms. Steam cell.

2. The vapor cell according to claim 1, wherein the cell window is substantially optically transparent to probe light.

3. The steam cell according to claim 1 or 2, wherein the cell window contains sapphire and the cell window has a coefficient of thermal expansion (CTE) greater than approximately parts per million degrees Celsius (ppm / °C).

4. The aforementioned anode junction comprises at least one of silicon or germanium, The vapor cell according to any one of claims 1 to 3, wherein the cell body comprises at least one of silicon or germanium.

5. The steam cell according to any one of claims 1 to 4, wherein the cell body and the cell window are nonreactive with the plurality of alkali atoms at a steam cell temperature exceeding approximately 150 degrees Celsius (°C).

6. The steam cell according to any one of claims 1 to 5, wherein the steam cell is configured to maintain a density of the plurality of alkali atoms in the steam cavity that is substantially constant as a function of temperature for steam cell temperatures above approximately 150°C.

7. A vapor cell according to any one of claims 1 to 6, further comprising a metal and an intermetallic alloy containing the plurality of alkali atoms.

8. The vapor cell according to claim 7, wherein the metal comprises at least one of gold or silver.

9. The steam cell according to claim 7 or 8, wherein the intermetallic alloy has an alloy decomposition temperature of approximately 150°C.

10. The steam cell according to any one of claims 7 to 9, further comprising a heater configured to heat the intermetallic alloy to at least the alloy decomposition temperature.

11. It is a sensor, steam cell The steam cell includes, The cell body and A cell window, wherein the cell window and the cell body are configured to define a vapor cavity and contain vapor containing a plurality of alkali atoms, Intermetallic alloys containing a metal and multiple alkali atoms, A detector configured to receive probe light transmitted through the vapor cell, Sensors, including

12. The sensor according to claim 11, wherein the cell window is substantially optically transparent to the probe light.

13. The sensor according to claim 11 or 12, wherein the cell window contains sapphire and the cell window has a coefficient of thermal expansion (CTE) greater than approximately 6 parts per million degrees Celsius (ppm / °C).

14. The sensor according to any one of claims 11 to 13, wherein the cell window is anode-bonded to the cell body.

15. The sensor according to claim 14, wherein the cell body comprises at least one of sapphire or germanium, and the anode junction comprises at least one of silicon or germanium.

16. The sensor according to any one of claims 11 to 15, wherein the cell body and cell window are nonreactive with the plurality of alkali atoms at a vapor cell temperature exceeding approximately 150 degrees Celsius (°C).

17. The sensor according to any one of claims 11 to 16, wherein the steam cell is configured to maintain a density of the plurality of alkali atoms in the steam cavity that is substantially constant as a function of temperature for a steam cell temperature above approximately 150°C.

18. The sensor according to any one of claims 11 to 17, wherein the metal comprises at least one of gold or silver.

19. The sensor according to any one of claims 11 to 18, wherein the intermetallic alloy has a decomposition temperature higher than approximately 150°C.

20. The sensor according to any one of claims 11 to 19, further comprising a heater configured to heat the alloy to at least the alloy decomposition temperature.

21. A method for manufacturing a steam cell, The arrangement involves placing at least one of silicon or germanium on at least one of the cell window or the cell body, wherein the cell window and the cell body define and define a vapor cavity. The cell window is anodic-bonded to the cell body via at least one of the silicon or germanium, Methods that include...

22. The glass is placed on at least one of the silicon, the germanium, the cell window, or the cell body. The cell window is anodic-bonded to the cell body via the glass, The method according to claim 21, further comprising:

23. The method according to claim 21 or 22, further comprising heating an intermetallic alloy containing a metal and a plurality of alkali atoms to an alloy decomposition temperature in the vapor cavity, thereby releasing at least a portion of the plurality of alkali atoms from the alloy as vapor in the vapor cavity.

24. It is a steam cell, The cell body and A cell window having a coefficient of thermal expansion (CTE) greater than approximately 6 parts per million degrees Celsius (ppm / °C), wherein the cell window is anodically bonded to the cell body. The cell window and the cell body are configured to define a vapor cavity and contain vapor containing a plurality of alkali atoms. The anode junction comprises at least one of silicon or germanium. The cell body and the cell window are nonreactive with the plurality of alkali atoms at a vapor cell temperature exceeding approximately 150 degrees Celsius (°C), and the cell window is... An intermetallic alloy comprising a metal and the plurality of alkali atoms, The aforementioned intermetallic alloy has an alloy decomposition temperature exceeding approximately 490°C, and A steam cell, including one.

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