DE102018000118B4 - Quantum chaotic magnetic field sensor and method for measuring a magnetic field - Google Patents

Abstract

Magnetic field sensor (100) for measuring a magnetic field (B), comprising: a measuring cell (1) which comprises an atomic vapor (2), the atomic vapor (2) having a spin system of spins of individual atoms; an optical manipulation device, which is designed to polarize the spin system in an initial state (AZ) by emitting light and to change a state of the spin system during a measurement process of the magnetic field (B) by emitting at least one optical kick pulse (KP), the at least one optical kick pulse (KP) generates a chaotic dynamic of the spin system; anda sensor device comprising: - an optical probe (4) which is designed to emit an optical test beam (TS) through the atomic vapor (2), and - an optical detector (3) which is designed to transmit the optical test beam (TS) to be measured by the atomic vapor (2).

Description

The invention relates to a magnetic field sensor and a method for measuring a magnetic field.

The invention is in the field of measurement technology, in particular in the field of quantum mechanical measurement technology and measurement technology for measuring magnetic fields.

Some of the most accurate magnetometers are based on the technology of optical atomic vapor magnetometers. These magnetometers typically comprise a vapor of alkali atoms (rubidium Rb, cesium Cs or potassium K) in a container, for example a glass flask. Alkali atoms have a nuclear spin I other than zero and a single electron in their valence shell. Their ground state is divided into hyperfine structure levels, which are characterized by a total angular momentum (spin) of j = I ± 1/2. With the help of an applied laser beam, the atoms can be brought into a desired state. In particular, this means that the atomic vapor in the container is polarized by optical pumping and thus has an oriented magnetic moment. An applied magnetic field or a magnetic field to be measured causes a precession of the magnetic moment of the atomic vapor. After a certain measuring time in which the magnetic moment rotates or precesses in the magnetic field B, the orientation of the magnetic moment is read out. To do this, one measures the transmission (intensity or polarization) of a test beam through the atomic vapor. In this way, information about the current alignment of the magnetic field can be obtained, whereby a measurement of the magnetic field is possible. In addition to the shot noise due to the optical readout, the accuracy of the measurement is typically limited by quantum mechanical effects as follows (standard deviation) [see Budker, Dmitry, and Michael Romalis, "Optical magnetometry", Nature Physics 3.4 (2007): pages 227-234 ]: $$\delta \mathrm{B.}=\frac{1}{G{\mu }_{\mathrm{B.}}}\frac{\hslash }{T_{\mathrm{M.}ess}\sqrt{N\mathrm{M.}}}$$

µ_B

Bohrsche Magneton

g

Lande-Faktor

ℏ

Planck'sches Wirkungsquantum

T_Mess

Messzeit

N

Anzahl der Atome des Atomdampfes

M

Anzahl der Wiederholungen der Messung

Somit liegt es nahe, durch eine Erhöhung der Messzeit T_Mess und/oder durch eine Erhöhung der Anzahl von Atomen N die Präzision der Messung zu verbessern bzw. die Standardabweichung δB zu verringern. Wie lange man messen kann bzw. wie groß T_Mess gewählt werden kann, ist jedoch durch die Kohärenzzeit beschränkt, die im Wesentlichen durch die Spin-Relaxationseffekte gegeben ist. Diese resultieren aus Stößen der Atome untereinander und Stößen der Atome mit der Wand. Auch die verwendbare Anzahl der Atome N ist beschränkt. Insbesondere führt eine Erhöhung der Anzahl der Atome N zu einer erhöhten Anzahl von Atomkollisionen, wodurch sich die Kohärenzzeit verringert.The following applies here:

µ _B

Bohr's Magneton

G

Landing factor

ℏ

Planck's quantum of action

T _meas

Measurement time

N

Number of atoms in atomic vapor

M.

Number of repetitions of the measurement

It therefore makes sense to improve the precision of the measurement or to reduce the standard deviation δB by increasing the measurement time T _{Mess and / or by increasing the number of atoms N.} How long one can measure or how large T _Mess can be selected, however, is limited by the coherence time, which is essentially given by the spin relaxation effects. These result from collisions between the atoms and the collisions between the atoms and the wall. The number of atoms N that can be used is also limited. In particular, an increase in the number of atoms N leads to an increased number of atomic collisions, as a result of which the coherence time is reduced.

For the measurement of very small magnetic fields (~ 10 ^-8 T; for comparison: the earth's magnetic field is more than three orders of magnitude larger) it is also possible to measure in a regime in which the negative effects of spin relaxation are suppressed. For such “spin-exchange-relaxation-free” (SERF) magnetometers, an accuracy of δB = 10 ^-15 T / Hz ^1/2 can be achieved.

US 8 421 455 B1 describes a magnetometer and accompanying magnetometry method comprising emitting light from a light source, pulsing the light from the light source using a pulse generator, directing the pulsed light to an atomic chamber, using a field sensor in the atomic chamber, and receiving a signal from the field sensor using a signal processing module.

US 2008/0 106 261 A1 describes a high-frequency tunable atomic magnetometer for the detection of nuclear quadrupole resonance (NQR) from solids at room temperature, including the detection of nitrogen-containing explosives which are arranged outside a sensor unit. A high frequency potassium magnetometer with a sensitivity of 0.24 fT / Hz ^1/2 is provided, operating at 423 kHz. Low intensity magnetic fields are measured using an alkali metal vapor by increasing the magnetic polarization of the steam to increase its sensitivity, then examining the magnetic polarization of the steam to obtain an output, and determining properties of the low intensity magnetic field from the output become.

US 2005/0 206 377 A1 describes a highly sensitive atomic magnetometer and method for measuring magnetic fields of low intensity, which relate to the use of an alkali metal vapor and a buffer gas; Increasing the magnetic polarization of the alkali metal vapor, thereby increasing the sensitivity of the alkali metal vapor to a low intensity magnetic field; Investigate the magnetic polarization of the alkali metal vapor, wherein the assay means provides an output from the alkali metal vapor, the output including properties related to the low intensity magnetic field; and measuring means receiving the output, determining the properties of the low intensity magnetic field, and providing a representation of the low intensity magnetic field.

Chaudhury, S., et al .: "Quantum signatures of chaos in a kicked top" (Nature, 2009, 461st vol., No. 7265, pp. 768-771 ) describes an experimental realization of a general paradigm for quantum chaos - the quantum kicked top - and the observation directly in the quantum phase space of dynamics, which have a chaotic classical counterpart. The system relies on the combined electronic and nuclear spins of a single atom and is therefore deep in the quantum regime. A good match between quantum dynamics and classical phase space structures is found. Since chaos is inherently a dynamic phenomenon, special importance is attached to dynamic signatures such as sensitivity to pertubation or generation of entropy and entanglement, for which only indirect evidence is available. Differences in sensitivity to pertubation in chaotic versus common, non-chaotic regimes is noted, and experimental evidence for dynamic entanglement as a signature of chaos is presented.

It is therefore the object of the present invention to provide a magnetic field sensor and a method for measuring a magnetic field with improved measuring accuracy. This object is achieved by a magnetic field sensor according to claim 1 and a method according to claim 17.

One aspect relates to a magnetic field sensor for measuring a magnetic field. The magnetic field sensor comprises a measuring cell which comprises an atomic vapor, wherein the atomic vapor has a spin system of spins of individual atoms, and an optical manipulation device which is designed to polarize the spin system in an initial state by emitting light and during a measuring process of the magnetic field to change a state of the spin system by emission of at least one optical kick pulse, the at least one optical kick pulse generating a chaotic dynamic of the spin system. The magnetic field sensor further comprises a sensor device, which comprises an optical probe, which is designed to emit an optical test beam through the atomic vapor, and an optical detector, which is designed to measure a transmission of the optical test beam through the atomic vapor.

The measuring cell can be designed so that a magnetic field to be measured with the magnetic field sensor can penetrate the measuring cell essentially unchanged from the measuring cell. The measuring cell can also be designed in such a way that the light emitted by the optical manipulation device and the optical kick pulse emitted by the optical manipulation device can penetrate the measuring cell essentially without loss or are essentially not absorbed by the measuring cell. For this purpose, the measuring cell can be designed as a glass cell. The measuring cell is also preferably embodied in a sealed manner or embodied in such a way that parts of the atomic vapor contained by the measuring cell cannot escape into an environment outside the measuring cell.

The measuring cell is preferably not limited to a specific size or a specific measuring cell volume. If the magnetic field sensor comprises an atomic vapor with a predetermined density, the number of atoms N can be set via the size of the measuring cell or its volume, whereby the measuring accuracy of the magnetic field sensor can be influenced, for example according to equation 1. On the other hand, a measuring cell that is as small as possible is advantageous, since this influences the spatial resolution of a magnetic field measurement or of the magnetic field sensor. The size or the volume of the measuring cell can thus be optimized for a specific application of the magnetic field sensor.

The measuring cell can preferably be designed with a variable measuring cell volume. Here, the volume can be set before and / or during a magnetic field measurement, preferably in a predetermined volume interval. Here, the measuring cell can, for example, have a movable wall, for example a piston wall, which can be moved relative to a point on the measuring cell in order to vary a volume of the measuring cell. In particular, this allows the volume of the measuring cell to be increased or decreased. In this way, a shape of the volume of the measuring cell can preferably be changed. The volume, its size and / or its shape can preferably be set dynamically by a user of the magnetic field sensor and / or by an external control system, for example based on determined environmental or measurement parameters.

The magnetic field sensor can furthermore preferably comprise an atomic vapor reservoir which is connected to the measuring cell, the atomic vapor reservoir being designed to at least partially absorb the atomic vapor. The atomic vapor reservoir is preferably connected to the measuring cell in this way, for example fluidically connected that an exchange of atomic vapor between the measuring cell and the atomic vapor reservoir is possible. The magnetic field sensor can furthermore comprise an atomic vapor exchange device, for example an atomic vapor pumping device, which is designed to move or pump at least part of the atomic vapor from the atomic vapor reservoir into the measuring cell and / or at least part of the atomic vapor from the To move or pump the measuring cell into the atomic vapor reservoir. As a result, in particular the number of atoms N of the atomic vapor in the measuring cell can be varied, in particular dynamically varied. The number of atoms N can preferably be set dynamically by the atomic vapor exchange device, for example the atomic vapor pumping device, by a user of the magnetic field sensor and / or by an external control system, for example based on established environmental or measurement parameters.

The measuring cell can also be designed with a heating device, the heating device being designed to keep the atomic vapor at a predetermined temperature. For this purpose, the heating device can comprise at least one heating element, for example heating coils and / or Peltier elements and / or electromagnetic heating elements. For this purpose, the heating device can furthermore comprise at least one thermometer element and at least one temperature control element. The at least one thermometer element is designed to measure a temperature of the atomic vapor or of an object which is thermally coupled to the atomic vapor in a known manner and from whose temperature the temperature of the atomic vapor can be determined and thus to determine the temperature of the atomic vapor . The determined temperature of the atomic vapor can be transmitted to the at least one temperature control element, which is designed to control the at least one heating element based on the determined temperature of the atomic vapor such that the temperature of the atomic vapor corresponds to a predetermined value.

The atomic vapor is arranged in the measuring cell or surrounded by it. The atomic vapor is designed in particular as a measuring probe of the magnetic field sensor, which is sensitive to magnetic fields, with spins of atoms in the atomic vapor in particular forming the measuring probe. In this sense, sensitive to magnetic fields is to be understood as meaning that a small variation in the magnetic field leads to an, in particular measurable, change in the dynamics of the spins in the magnetic field and thus to a changed final state of the measuring probe. A sensitivity of the measuring probe depends on the change in the final state, the greater the change in the final state, the more sensitive the measuring probe or the magnetic field sensor. In particular, the maximum achievable sensitivity can be quantified by an overlap between the quantum mechanical end state disturbed by the variation of the magnetic field and the intact or undisturbed initial state. In particular, this overlap is directly related to the achievable measurement accuracy via the quantum Fisher information.

A spin system of spins of individual atoms is to be understood here as a group of two or more spins. In particular, the spin system comprises the nuclear spins of the atomic vapor, the atomic vapor forming the measuring probe of the magnetic field sensor.

The optical manipulation device is designed to polarize the spin system in an initial state by emitting light. Here, the optical manipulation device is designed to emit at least one optical polarization signal, the at least one optical polarization signal passing through the atomic vapor and polarizing the spins of the spin system. The initial state of the spin system is the state of the spin system after the spins of the spin system have been polarized by the optical manipulation device. The at least one polarization signal preferably has a frequency so that the at least one polarization signal is resonant to a first electronic transition of the atoms of the atomic vapor. In the context of this description, an electronic transition is to be understood as a change in the energy level of an electron in an atom of atomic vapor.

Vorzugsweise weist der Gesamtpolarisationsgrad p des Spin-Systems einen Wert von mindestens 10%, bevorzugt mindestens 50%, weiter bevorzugt mindestens 80%, am meisten bevorzugt mindestens 90% auf.Complete polarization of the spin system is preferred, but not absolutely necessary. Incomplete polarization leads to an effective reduction in the spins or atoms contributing to the measurement signal, so that the number of atoms in the atomic vapor N has to be replaced by Np, where p is the total degree of polarization of the spin system. Here p _i can be the individual degree of polarization of a spin of the spin system, whereby the total degree of polarization results from: $$p=\frac{1}{N}{\displaystyle \sum _{i=1}^N{p}_i}$$

The total degree of polarization p of the spin system preferably has a value of at least 10%, preferably at least 50%, more preferably at least 80%, most preferably at least 90%.

The optical manipulation device is also designed to emit at least one optical kick pulse. The optical kick pulse is designed to interact with the spin system of the atomic vapor through electron-photon interaction and thus to change a state of the spin system, in particular the initial state of the spin system. Before the optical manipulation device emits the at least one optical kick pulse, the spin system of the atomic vapor can be described as a quantum mechanical top. This is given by an angular momentum or spin, the amount of which is retained, whereby the quantum mechanical gyroscope can in particular describe a precessing atomic spin in a magnetic field. The at least one optical kick pulse in particular disrupts this regular dynamic of the precessing atomic spins in a magnetic field. In particular, in the case of the at least one optical kick pulse, an angular momentum state or spin state is rotated to different degrees depending on the position of the spin in a state space of the spin. This leads to a distortion of the state, which makes the regular dynamics chaotic in the classic limit case. In the context of this description, a classically chaotic system is to be understood as a system whose development over time cannot be predicted with arbitrary precision over at least a limited time interval. In particular, dynamics which have a mixed chaotic-regular phase space are also referred to as chaotic in the context of this description. The optical manipulation device is thus designed to generate or establish a chaotic dynamics of the spin system. The at least one optical kick pulse also has a frequency such that the at least one kick pulse is detuned relative to an electronic transition of the atoms of the atomic vapor.

Here, the chaotic dynamics of the spin system is created based on the AC-Stark effect. In particular, a light pulse, for example a polarization signal and / or a kick pulse and / or a test beam, can traverse the spin system or the atomic vapor once. The magnetic field sensor can furthermore have a light guide device which guides at least one light pulse in such a way that the at least one light pulse traverses the spin system or the atomic vapor at least twice. In particular, a chaotic dynamic can be generated through an interaction of the test beam with the atomic vapor based on the Faraday effect or based on paramagnetic Faraday rotation of the polarization of a linearly polarized test beam at least twice. For this purpose, the light-guiding device can for example at least partially have mirrors and / or glass fibers and / or waveguides. Alternatively or additionally, the optical manipulation device can be designed to emit squeezed light. In this sense, squeezed light is to be understood as electromagnetic radiation whose quantum mechanical fuzziness has been asymmetrically changed. Either the uncertainty of the amplitude of the electromagnetic radiation at the expense of the uncertainty of the phase of the electromagnetic radiation or the uncertainty of the phase of the electromagnetic radiation at the expense of the uncertainty of the amplitude of the electromagnetic radiation can be changed. The squeezed state of the squeezed light can be at least partially transferred to the spin system through interaction with the spin system, whereby a chaotic dynamics of the spin system can be produced. In particular, the optical manipulation device can alternatively or additionally be designed in such a way that it produces a chaotic dynamic of the spin system on the basis of an effective non-linear interaction between individual spins.

The optical manipulation device can also be designed so that an emission direction of the at least one polarization signal is essentially orthogonal to an emission direction of the at least one optical kick pulse. In particular, the optical manipulation device can also be designed so that at least one point in the measuring cell is passed through or reached by the at least one optical polarization signal and the at least one optical kick pulse.

In particular, a polarization volume can be defined, the polarization volume comprising all spins of the spin system or atoms of the atomic vapor which are polarized by the at least one polarization signal. In this case, the polarization volume can in particular include all spins of the spin system or atoms of the atomic vapor, which are caused by a spin photon Interaction or electron-photon interaction are polarized with the at least one polarization signal, and optionally include all spins of the spin system or atoms of atomic vapor, which by a spin-spin interaction or atom-atom interaction based on the at least polarized a polarization signal.

In particular, a chaos volume can be defined, the chaos volume comprising all spins of the spin system or atoms of the atomic vapor which interact with the at least one optical kick pulse through spin-photon interaction or electron-photon interaction. Here, the chaos volume can in particular include all spins of the spin system or atoms of the atomic vapor, which interact with the at least one optical kick pulse by spin-photon interaction or electron-photon interaction, and optionally all spins of the spin system or Include atoms of the atomic vapor, which interact through a spin-spin interaction or atom-atom interaction based on the at least one optical kick pulse.

The magnetic field sensor is preferably designed so that an intersection between the polarization volume and the chaos volume comprises at least one element or one spin or one atom of atomic vapor. A number of the elements of the intersection can represent the number of atoms N from equation 1.

The optical probe is designed to emit a test beam through the measuring cell or through the atomic vapor. Here the optical probe can be designed to emit coherent and / or monochromatic electromagnetic radiation. In particular, the optical probe can be designed as a measuring laser. Preferably, the optical probe is further configured to emit the test beam with a low intensity. For example, the optical probe can generate a test beam with an intensity of at least 0.1 mW / cm ² , preferably of at least 0.3 mW / cm ² , most preferably of at least 0.4 mW / cm ² and of a maximum of 5 mW / cm ² , preferably of a maximum of 1 mW / cm ² , most preferably of a maximum of 0.6 mW / cm ² . The optical test beam has a measuring frequency, the measuring frequency being set as a function of a resonance of an electronic transition of the atomic vapor or the measuring probe. In particular, the measuring frequency is red-tuned to an electronic transition of the atomic vapor or the measuring probe.

The optical detector is designed to measure a transmission of the test beam through the atomic vapor or a physical quantity of the transmission of the test beam through the atomic vapor. For this purpose, the optical detector can have at least one photodiode. However, the optical detector is not limited to photodiodes, but can have at least any desired photodetector, for example a photodetector based on the internal and / or the external photoelectric effect. The optical detector can here preferably be designed to receive an optical signal or a transmission of the test beam through the atomic vapor and to convert it into an electrical data signal.

The optical detector is preferably designed to measure the transmission of the test beam during the chaotic dynamics of the spin system. In particular, this enables an improved measuring accuracy of the magnetic field compared to the measuring accuracy of a conventional atomic vapor magnetometer.

The optical manipulation device preferably comprises at least one pump laser which is designed to polarize the spin system in an initial state by emitting light. In particular, the pump laser is designed to emit the at least one optical polarization signal. In particular, at least one monochromatic and coherent optical polarization signal can be emitted by the at least one pump laser, which enables high measurement accuracy and reliable reproducibility of a measurement. The at least one pump laser is preferably configured to emit circularly polarized light.

The optical manipulation device preferably comprises at least one kick laser which is designed to emit the at least one optical kick pulse. In particular, at least one monochromatic and coherent optical kick pulse can be emitted by the at least one kick laser, which enables a high level of measurement accuracy and reliable reproducibility of a measurement. Furthermore, the at least one kick laser enables precise control or controlled maintenance of the chaotic dynamics of the atomic vapor or the spin system. The at least one kick laser is preferably configured to emit linearly polarized light.

The at least one kick laser is preferably configured to emit the optical kick pulse parallel to the optical test beam. Alternatively, the at least one kick laser is configured so that a path of the test beam and a path of the at least one optical kick pulse intersect.

The kick laser or the optical manipulation device is preferably configured to emit the test beam or be designed as the optical probe. Thus, the kick laser or the optical manipulation device can take on the role of the optical probe or can also be designed as an optical probe. For this purpose, the kick laser is configured to emit laser light with adjustable, variable intensity. Preferably, the kick laser can also be configured to emit at least one first optical kick pulse and at least one last optical kick pulse, the optical detector at least partially measuring the last optical kick pulse in order to measure an external magnetic field.

Alternatively, the optical probe can be designed as at least one kick laser, the optical probe is designed here to emit the at least one optical kick pulse.

The test beam and / or the at least one optical kick pulse are preferably aligned in such a way that an interaction, in particular based on the AC Stark effect, between the test beam and / or the at least one optical kick pulse with the spins of the spin system or with the atoms of the atomic vapor is caused or occurs. The polarization of the spins of the spin system or of the atoms of the atomic vapor can preferably be aligned before the measurement or the measuring process of a magnetic field in order to ensure such an interaction.

In particular, a test volume can be defined, the test volume comprising all spins of the spin system or atoms of the atomic vapor which interact with the one optical test beam by spin-photon interaction or electron-photon interaction.

An alignment direction or alignment of the pump laser or an alignment of the at least one polarization signal preferably forms an acute or right angle with the external magnetic field or with the magnetic field to be measured. Preferably, an alignment direction or alignment of the polarization of the kick laser or an alignment of the polarization of the at least one optical kick pulse forms an acute or right angle with the external magnetic field or with the magnetic field to be measured.

The magnetic field sensor preferably comprises at least one magnetic field device which is designed to generate magnetic field pulses in the measuring cell. For this purpose, the magnetic field device can comprise at least one magnetic field coil which is arranged around the measuring cell. In particular, the magnetic field device is designed to rotate or rotate the initial state of the spin system or the spins of the spin system and / or thus to align it along a desired direction. In particular, the magnetic field device is designed to rotate or rotate the initial state of the spin system or the spins of the spin system polarized by the optical manipulation device and / or thus to align it along a desired direction.

The at least one kick laser, the at least one pump laser and the optical probe can preferably be aligned in parallel, so that the at least one kick pulse, the at least one polarization signal and the at least one test beam are emitted essentially in parallel. In this way, in particular, an additional rotation or alignment of the initial state of the spin system, for example by the at least one magnetic field device, can be omitted.

The optical manipulation device is preferably designed to maintain the chaotic dynamics of the spin system by emitting at least one further optical kick pulse, the optical manipulation device being designed to emit the at least one further optical kick pulse at essentially periodic time intervals. The at least one further optical kick pulse can be designed to be identical to the at least one optical kick pulse, particularly with regard to frequency and / or intensity and / or duration. Even if the at least one further optical kick pulse can differ from the at least one optical kick pulse, statements on the at least one optical kick pulse in this description can in principle also be applied to the at least one further optical kick pulse, unless expressly stated otherwise.

An intensity of the optical kick pulse preferably has a rectangular function and / or a triangular function and / or a non-linear function. This means that, if the intensity of the optical kick pulse has a rectangular function, the intensity is set to around 100% of a kick laser intensity during an entire kick length essentially at the beginning of the kick length and is kept at around 100% of a kick laser intensity until the end of the kick length . It is also to be understood that, if the intensity of the optical kick pulse has a triangular function, the intensity increases essentially linearly over an entire kick length from about 0% of the kick laser intensity to about 100% of the kick laser intensity and then by about 100% until the end of the kick length the kick laser intensity is reduced essentially linearly to about 0% of the kick laser intensity. Here, the intensity of the optical kick pulse can be kept between the essentially linear increase and the essentially linear reduction of the intensity to approximately 100% of the kick laser intensity. It is also to be understood that, if the intensity of the optical kick pulse has a non-linear function, the intensity is increased essentially non-linearly to about 100% of the kick laser intensity during an entire kick length from about 0% of the kick laser intensity and / or subsequently up to At the end of the kick length of approximately 100% of the kick laser intensity is reduced essentially non-linearly to approximately 0% of the kick laser intensity. The intensity of the optical kick pulse can be kept between the increase and the reduction of the intensity to about 100% of the kick laser intensity. In the context of the invention, the kick length is to be understood as the laser irradiation time of the kick laser per optical kick pulse or per measurement period. The kick laser intensity represents a set maximum irradiation intensity of the kick laser.

The optical detector is preferably designed to measure an intensity and / or a polarization of the transmission of the test beam. The external magnetic field can be calculated or estimated on the basis of the intensity and / or the polarization of the transmission of the test beam.

The atomic vapor preferably comprises alkali atoms, preferably ¹³³ Cs atoms. Alkali atoms have a single free electron in the valence shell and are therefore particularly suitable as atomic vapor of the magnetic field sensor.

The atomic vapor can preferably comprise at least one protective gas, preferably helium and / or nitrogen. In particular, helium can act as a buffer gas and thus reduce diffusion or collisions of the atomic vapor with the walls of the measuring cell or reduce impairment of the spin system due to collisions or angular momentum transfers with the walls of the measuring cell. In particular, nitrogen can act as a protective gas and thus reduce radiation interactions between the atoms of the atomic vapor or within the spin system.

The atomic vapor preferably has a density of at least about 10 ⁴ atoms / cm ³ , preferably of at least about 109 atoms / cm ³ , and / or of a maximum of about 10 ¹⁵ atoms / cm ³ , preferably of a maximum of about 10 ¹¹ atoms / cm ³ .

The initial state is preferably a hyperfine state or a mixed state of hyperfine states of the spin system.

The optical manipulation device is preferably designed to polarize and / or generate the initial state by means of a circularly polarized light field.

The magnetic field sensor preferably has a total volume, the total volume being scalable according to the area of application. Thus, a chip-based embodiment of the magnetic field sensor, a total volume of at least 0.01cm ^3, preferably at least 0.1cm ^3, more preferably at least 1 cm ³ and a maximum of 10cm ^3, preferably 5 cm ^3, more preferably 2cm ³ have. However, the total volume can be adapted to the application. Thus, the magnetic field sensor can be vehicle-supported and / or aircraft-supported and / or drone-supported and / or satellite-supported.

Another aspect relates to a method for measuring a magnetic field, comprising providing a measuring cell which comprises an atomic vapor, the atomic vapor having a spin system of spins of individual atoms. The method further comprises polarizing the spin system in an initial state by means of an optical manipulation device. The method further comprises generating chaotic dynamics of the spin system by outputting at least one optical kick pulse from the manipulation device to the spin system. The method further includes generating an optical test beam from an optical probe through the atomic vapor. The method further includes measuring a transmission of the test optical beam through the atomic vapor from an optical detector that receives the test optical beam.

The measuring cell and / or the optical manipulation device and / or the optical probe and / or the optical detector can be designed according to the magnetic field sensor described above.

The method preferably further comprises rotating the initial state, after polarizing the spin system and before generating the chaotic dynamics, by generating at least one magnetic field pulse by at least one magnetic field device. This enables a controlled and well-defined initial state before the emission of the at least one optical kick pulse. The magnetic field device can be designed in accordance with the magnetic field sensor described above.

Preferably, the method further comprises rotating a state of the spin system, after generating the optical test beam and before measuring the transmission, by generating at least one magnetic field pulse by at least one magnetic field device. As a result, the spin system can be rotated by an optical detector into an optimal final state for reading out or measuring the transmission of the optical test beam through the atomic vapor. The magnetic field device can be designed in accordance with the magnetic field sensor described above.

A first exemplary embodiment, referred to below as “Example 1”, is described and compared with a reference measurement method or reference method.

A measuring cell or glass cell contains a droplet of ¹³³ Cs metal, which has a density of about 2 * 10 ¹⁰ / cm ³ and forms a spin system, with the cesium forming an atomic cloud or atomic vapor.

A pump laser is aimed at the glass cell and ^{tuned to the D1 electronic transition of the 133} Cs atomic vapor. In particular, the pump laser polarizes the atomic vapor or the spin system at the beginning of the measurement process along the X axis. The pump laser is set to a frequency of 335.116048807 THz (resonant to the D1 transition) and configured to emit circularly polarized light.

To describe the initial state of the spin system in a mathematical state space, spherical coordinates with polar angle θ ∈ [0, π), plotted from the positive Z-axis, and azimuthal angle φ ∈ [0, 2π), plotted from the positive X-axis, used.

For the implementation of the reference measurement, the measurement dynamics are given by the precession of the spin system in the magnetic field (in the Z direction). The status is read out after a measurement process. In the implementation under consideration, this takes place by means of polarization measurement, a polarization plane of a linearly polarized red detuned test beam, which is emitted by a measuring laser, being rotated and then measured using photodiodes.

For example 1 and the reference method, the measuring laser is set to a frequency which is red-detuned to a D2 transition of ¹³³ Cs, and configured to emit linearly polarized light or a linearly polarized test beam. An intensity of the test beam is set to 0.5 mW / cm ² .

The magnetic field sensor from example 1 further comprises magnetic field coils which are arranged around the glass cell. The magnetic field coils are designed to generate a magnetic field pulse at least in the glass cell. Since a polarized state of the spin system precesses in the magnetic field, the state of the spin system can thus be rotated to a desired position. In the measurement method used in example 1, this is done before a measurement dynamic. The measurement dynamics are described in more detail below.

• I = 7/2, der Kernspin;
• f = 3, 4, Hyperfeinstruktur-Quantenzahlen des Grundzustands;
• f'= 3, 4, Hyperfeinstruktur-Quantenzahlen des angeregten Zustands;
• g(f = 3) = -1/4; g(f = 4) =1/4, gyromagnetisches Verhältnis;
• Γ = 4.561257 MHz, natürliche Linienbreite des D1 Übergangs;
• Δ_ground = 9.192631770 GHz, Hyperfeinaufspaltung des Grundzustands;
• Δ_exciled = 1167.680 MHz, Hyperfeinaufspaltung des angeregten Zustands;
• I_sat = 2.498122 mW/cm², Sättigungsintensität für stark verstimmtes π-polarisiertes Licht.

The spin system and the D1 electronic transition of ¹³³ Cs have the following key data in the context of example 1:

• I = 7/2, the nuclear spin;
• f = 3, 4, hyperfine structure quantum numbers of the ground state;
• f '= 3, 4, hyperfine structure quantum numbers of the excited state;
• g (f = 3) = -1/4; g (f = 4) = 1/4, gyromagnetic ratio;
• Γ = 4.561257 MHz, natural line width of the D1 transition;
• Δ _ground = 9.192631770 GHz, hyperfine splitting of the ground state;
• Δ _exciled = 1167.680 MHz, hyperfine splitting of the excited state;
• I _sat = 2,498,122 mW / cm ² , saturation intensity for strongly detuned π-polarized light.

To implement the magnetic field sensor, the implementation of the reference measurement is supplemented by a kick laser, which is designed to emit at least one optical kick pulse into the spin system parallel to the measuring laser. The laser light from the kick laser is linearly polarized in the X direction and red-tuned to the D1 transition. The at least one optical kick pulse can be repeated at predetermined time intervals, preferably periodically. As in the reference measurement, the state is read out and thus the magnetic field is measured or estimated.

External parameters and settings of the kick laser are as follows:

• - Detuning of the kick laser to the D1 transition: $$\Delta =-{\Delta }_{excited}/2=-583.84\text{MHz};$$
  
• - Kick laser intensity: I _kick ≅ 0.1 mW / cm ² ;
• - Kick laser frequency: 335.116048807 THz - 583.84 MHz;

• - Magnetic field to be measured: B = 4 * 10 ^-14 T;
• Alignment of the initial polarized state: θ = π / 2rad; φ = π / 2rad (so that the initial state points in the y-direction);
• - Period duration (kick and precession): r = 1 ms;
• - Duration of a single kick: T _Kick = 2 * 10 ^-6 s;
• - Angle of rotation of the state about the Z axis immediately before the polarization measurement: ϑ = π / 2rad;
• - temperature: T = 21 ° C;
• - Radius of the measuring cell: r = 1.5 cm;
• - (optimal) number of periods of the measurement dynamics: N _Kick = 87354;
• - (optimal) number of periods for the reference _{measurement: N Ref} = 144056;
• - Density of atomic vapor 2 * 10 ¹⁰ atoms / cm ³

1. 1. Polarisieren der Spins des Spin-Systems in einem Anfangszustand durch Emission von mindestens einem Polarisierungssignals durch den Pumplaser;
2. 2. Rotieren des Anfangszustands durch Emission von mindestens einem Magnetfeldpuls über die mindestens eine Magnetfeldspule;

Beginn der Messdynamik

• 3. Durchführen einer Messdynamik über N_Kick Perioden. Hierbei besteht jede Periode aus einer Präzessionszeit der Spins und einem darauffolgenden optischen Kickpuls der Länge T_Kick;

Ende der Messdynamik

• 4. Rotieren des Zustands des Spin-Systems um einen Winkel ϑ nach der Messdynamik durch Emission von mindestens einem Magnetfeldpuls über die mindestens eine Magnetfeldspule;
• 5. Auslesen bzw. Messen eines Endzustands des Spin-Systems mittels Polarisationsmessung;
• 6. Wiederholen des Messverfahrens von Schritt 1 bis Schritt 5, wobei die Wiederholung beliebig oft wiederholt werden kann;
• 7. Schätzung bzw. Berechnung des zu messenden Magnetfeldes aus den Messergebnissen, beispielsweise mittels einer Maximum-Likelihood-Methode.

A measurement of the magnetic field to be measured using one as described above Magnetic field sensor takes place according to the following steps in the given order:

1. 1. Polarizing the spins of the spin system in an initial state by emission of at least one polarization signal by the pump laser;
2. 2. Rotation of the initial state by emission of at least one magnetic field pulse via the at least one magnetic field coil;

Beginning of the measurement dynamics

• 3. Performing a dynamic measurement over N _kick periods. Each period consists of a precession time of the spins and a subsequent optical kick pulse of length T _kick ;

End of measurement dynamics

• 4. Rotating the state of the spin system by an angle ϑ according to the measurement dynamics by emitting at least one magnetic field pulse via the at least one magnetic field coil;
• 5. Reading out or measuring a final state of the spin system by means of polarization measurement;
• 6. Repeat the measurement procedure from step 1 up step 5 , whereby the repetition can be repeated as often as desired;
• 7. Estimation or calculation of the magnetic field to be measured from the measurement results, for example by means of a maximum likelihood method.

1. 1. Polarisieren der Spins des Spin-Systems in einem Anfangszustand durch Emission von mindestens einem Polarisierungssignals durch den Pumplaser;
2. 2. Rotieren (optional) des Anfangszustands durch Emission von mindestens einem Magnetfeldpuls über die mindestens eine Magnetfeldspule;

Beginn der Messdynamik

• 3. Durchführen einer Messdynamik über N_Ref Perioden, lediglich bestehend aus einer Präzessionszeit der Spins;

Ende der Messdynamik

• 4. Rotieren (optional) des Zustands des Spin-Systems um einen Winkel 9 nach der Messdynamik durch Emission von mindestens einem Magnetfeldpuls über die mindestens eine Magnetfeldspule;
• 5. Auslesen bzw. Messen eines Endzustands des Spin-Systems mittels Polarisationsmessung;
• 6. Wiederholen des Messverfahrens von Schritt 1 bis Schritt 5, wobei die Wiederholung beliebig oft wiederholt werden kann;
• 7. Schätzung bzw. Berechnung des zu messenden Magnetfeldes aus den Messergebnissen, beispielsweise mittels einer Maximum-Likelihood-Methode.

A measurement of the magnetic field to be measured using the reference method is carried out according to the following steps in the specified order:

1. 1. Polarizing the spins of the spin system in an initial state by emission of at least one polarization signal by the pump laser;
2. 2. Rotation (optional) of the initial state by emission of at least one magnetic field pulse via the at least one magnetic field coil;

Beginning of the measurement dynamics

• 3. Performing a measurement dynamic over N _Ref periods, consisting only of a precession time of the spins;

End of measurement dynamics

• 4. Rotate (optional) the state of the spin system by an angle 9 according to the measurement dynamics by emission of at least one magnetic field pulse via the at least one magnetic field coil;
• 5. Reading out or measuring a final state of the spin system by means of polarization measurement;
• 6. Repeat the measurement procedure from step 1 up step 5 , whereby the repetition can be repeated as often as desired;
• 7. Estimation or calculation of the magnetic field to be measured from the measurement results, for example by means of a maximum likelihood method.

In a comparison between a measuring method using optical kick pulses with the reference method under comparable conditions, an approximately 68% improvement in the measuring accuracy compared to the reference method can be determined. The detailed simulation results are 2 and the corresponding description of the figures.

• 1: Eine schematische Darstellung einer Messdynamik zur Messung eines Magnetfeldes auf Basis von optischen Kickpulsen;
• 2: Eine schematische Darstellung eines Magnetfeldsensors mit einer optischen Manipulations-Einrichtung;
• 3: Eine graphische Darstellung der Messgenauigkeit für verschiedene Magnetfeld-Messmethoden basierend auf Beispiel 1.

The invention is further described below by exemplary embodiments shown in the figures. Show it:

• 1 : A schematic representation of a measurement dynamics for measuring a magnetic field based on optical kick pulses;
• 2 : A schematic representation of a magnetic field sensor with an optical manipulation device;
• 3 : A graphical representation of the measurement accuracy for various magnetic field measurement methods based on Example 1.

1 a schematic representation of a measurement dynamics for measuring a magnetic field based on optical kick pulses KP . Here, a measuring cell encloses an atomic vapor in an initial state AZ . The initial state AZ can be a polarized initial state AZ be. The measuring cell and the atomic vapor comprised by the measuring cell in the initial state AZ are exposed to an external magnetic field. This causes a precession R _z (α) the spins of atomic vapor take place. This (regular) precession R _z (α) is at least once by an optical kick pulse KP interrupted. Depending on the position of a spin of the atomic vapor in a state space of the spin, an angular momentum state of the spin is rotated to different degrees, which creates a chaotic dynamic. The optical kick pulses KP can be emitted periodically or at identical time intervals or aperiodically or at different time intervals. After a predetermined number of optical kick pulses KP the system reaches a final state EZ which is read out or measured by means of an intensity and / or polarization measurement of a test beam emitted by the atomic vapor. The measurement dynamics can be as often as required are repeated, the external magnetic field being calculated or estimated on the basis of the measured values. This can be achieved, for example, using a maximum likelihood method.

2 a schematic representation of an exemplary magnetic field sensor 100 with an optical manipulation device. The magnetic field sensor 100 is here arranged schematically in an XY plane, but is not limited to such an arrangement. Here is an external magnetic field to be measured B. exemplarily aligned parallel to the Z-axis. The external magnetic field B. here penetrates the magnetic field sensor 100 , the magnetic field sensor 100 preferably the external magnetic field B. essentially unchanged. Essentially, in the context of this description is to be understood as comprehensively low manufacturing and environmental-related deviations.

The magnetic field sensor 100 furthermore comprises a measuring cell 1 , the measuring cell 1 exemplarily centrally within the magnetic field sensor 100 is arranged. In particular, the external magnetic field penetrates B. the measuring cell 1 , the measuring cell 1 preferably the external magnetic field B. essentially unchanged. The measuring cell 1 can be designed in particular spherical or cylindrical. The measuring cell 1 can be formed from a material transparent to electromagnetic radiation, the material transparent to electromagnetic radiation being in particular formed in such a way that the material transparent to electromagnetic radiation is particularly suitable for electromagnetic radiation or laser light of an optical manipulation device or a pump laser 5 and a kick laser 6th , and / or an optical probe 4th is transparent, which are further described below.

The measuring cell 1 includes or surrounds an atomic vapor 2 . The measuring cell can 1 be designed in such a way that no chemical reactions between the measuring cell 1 or a measuring cell wall and the atomic vapor 2 can take place. The measuring cell 1 is preferably designed to be sealed or designed in such a way that parts of the through the measuring cell 1 included atomic vapor 2 not in an environment outside of the measuring cell 1 can escape. The measuring cell 1 is preferably designed such that parts of the through the measuring cell 1 included atomic vapor 2 not in a material of the measuring cell 1 can penetrate and / or that parts of the through the measuring cell 1 included atomic vapor 2 not in a material of the measuring cell 1 be able to store or intercalate.

The atomic vapor 2 is in the measuring cell 1 arranged or surrounded by them. The atomic vapor 2 is in particular as a measuring probe of the magnetic field sensor 100 which are sensitive to magnetic fields B. is formed, in particular spins of atoms of atomic vapor 2 form the measuring probe. The atomic vapor 2 preferably comprises alkali atoms, preferably ¹³³ Cs atoms, with other atoms from the atomic vapor as well 2 can be included. In particular, the atomic vapor 2 comprise a mixture of atoms of at least two different elements and / or of at least two different isotopes.

The atomic vapor 2 can comprise at least one protective gas, preferably helium and / or nitrogen, the at least one protective gas, for example, a diffusion or collision of the atoms of the atomic vapor 2 with the walls of the measuring cell 1 reduced or impairment of the spin system due to collisions or angular momentum transfers with the walls of the measuring cell 1 reduced and / or radiation interactions between the atoms of atomic vapor 2 or reduced within the spin system. Alternatively, the measuring cell 1 on at least one surface of the measuring cell 1 , especially within the measuring cell 1 , be coated with at least one protective layer, the at least one protective layer, for example, a diffusion or collision of the atoms of the atomic vapor 2 with the walls of the measuring cell 1 reduced or impairment of the spin system due to collisions or angular momentum transfers with the walls of the measuring cell 1 reduced and / or the measuring cell 1 protects from damage and wear. The at least one protective layer can have at least one protective film based on paraffin and / or at least one protective film based on alkenes, for example 1-nonadecs (see, for example, US 2012/0 112 749 A1).

The atomic vapor 2 can have a density of at least about 10 ⁴ atoms / cm ³ , preferably of at least about 10 ⁹ atoms / cm ³ , and of a maximum of about 10 ¹⁵ atoms / cm ³ , preferably of a maximum of about 10 ¹¹ atoms / cm ³ . In particular, the atomic vapor 2 have a variable density, the density of the atomic vapor 2 through or via the magnetic field sensor 100 can be adjusted.

The magnetic field sensor 100 comprises an optical manipulation device. The optical manipulation device is designed to reduce the spin system in the initial state by emitting light AZ to polarize. Here, the optical manipulation device is designed to have at least one optical polarization signal PS to emit, the at least one optical polarization signal PS the atomic vapor 2 and polarizes the spins of the spin system. For this purpose, the optical manipulation device can have at least one polarization laser or a pump laser 5 have, the at least one pump laser 5 is designed the at least one polarization signal PS to emit. The at least one pump laser 5 is in particular designed such that the at least one polarization signal PS preferably has a frequency so that the at least one polarization signal PS resonant to a first electronic transition of the atoms of atomic vapor 2 is. The pump laser 5 can be designed in particular to bring about a complete or a partial polarization of the spins of the spin system. The total degree of polarization p of the spin system preferably has a value of at least 10%, preferably at least 50%, more preferably at least 80%, most preferably at least 90%.

The optical manipulation device is designed to have at least one optical kick pulse KP to emit. The optical kick pulse KP is especially designed through electron-photon interaction with the spin system of atomic vapor 2 to interact and thus a state of the spin system, especially the initial state AZ of the spin system. The optical manipulation device is thus designed to generate or establish a chaotic dynamics of the spin system. The at least one optical kick pulse KP preferably has a frequency which is lower than the at least one polarization signal PS .

The optical manipulation device preferably comprises at least one kick laser 6th , which is designed, the at least one optical kick pulse KP to emit. With at least one kick laser 6th can in particular at least one monochromatic and coherent optical kick pulse KP are emitted. Furthermore, the at least one kick laser enables 6th in particular a precise control of the state or a controlled maintenance of the chaotic dynamics of the atomic vapor 2 or the spin system. The at least one kick laser is preferably used 6th configured to emit linearly polarized light.

The optical manipulation device is designed in particular so that a polarization direction of the at least one polarization signal PS essentially orthogonal to an emission direction of the at least one optical kick pulse KP is. In particular, the optical manipulation device can preferably be designed so that at least one point in the measuring cell 1 by the at least one optical polarization signal PS and by the at least one optical kick pulse KP is passed through or reached. Or the pump laser 5 and the kick laser 6th in particular be aligned so that the polarization signal PS and the at least one optical kick pulse KP at one point within the measuring cell 1 can cross.

In particular, a polarization volume can be defined, the polarization volume being all spins of the spin system or atoms of atomic vapor 2 comprises which by the at least one polarization signal PS be polarized. Furthermore, a chaos volume can in particular be defined, the chaos volume having all spins of the spin system or atoms of atomic vapor 2 includes which with the at least one optical kick pulse KP interact by spin-photon interaction or electron-photon interaction. The magnetic field sensor 100 is preferably designed so that an intersection between the polarization volume and the chaos volume is at least one element or one spin or one atom of atomic vapor 2 includes.

The magnetic field sensor 100 comprises a sensor device, the sensor device being an optical probe 4th includes. The optical probe 4th is designed to use a test beam TS through the measuring cell 1 or by the atomic vapor 2 to emit.

Here the optical probe 4th in particular be designed to emit coherent and / or monochromatic electromagnetic radiation. In particular, the optical probe 4th be designed as a measuring laser. Preferably the optical probe is 4th further configured the test beam TS to emit with a low intensity. The optical test beam TS preferably has a measuring frequency, the measuring frequency depending on a resonance of an electronic transition of the atomic vapor 2 or the measuring probe is set.

The sensor device further comprises an optical detector 3 , the optical detector 3 is designed, a transmission of the test beam TS through the atomic vapor 2 or a physical quantity of the transmission of the test beam TS through the atomic vapor 2 to eat. The optical detector can do this 3 an example of a signal splitter 9 have, which is designed, an optical signal received by the signal splitter or the transmission of the test beam TS through the atomic vapor 2 divide into two, preferably identical, signal parts in particular. A first signal part is sent to a first photodiode 10A and a second signal part is sent to a second photodiode 10B which convert the received signal part into a first or second electrical data signal and this to an evaluation unit 11 conduct. The optical detector 3 is not limited to photodiodes, but can have at least any desired photodetector, for example a photodetector based on the internal and / or the external photoelectric effect. The evaluation unit 11 receives the first and second data signals, respectively, and determines the external one based on the first and second data signal Magnetic field B. . Here is the optical detector 3 preferably designed, the transmission of the test beam TS to measure during the chaotic dynamics of the spin system.

The optical detector 3 can preferably be designed a position of the transmission of the test beam TS through the atomic vapor 2 at which the transmission of the test beam TS through the atomic vapor 2 hits the optical detector to determine. The magnetic field sensor 100 can preferably be a position of the optical probe 4th determine or determine. Alternatively, the position of the optical probe 4th be stored in the magnetic field sensor. In particular, the magnetic field sensor 100 based on the position of the optical probe 4th and the position of the transmission of the test beam TS through the atomic vapor 2 at which the transmission of the test beam TS through the atomic vapor 2 on the optical detector 3 hits a beam path of the test beam TS determine. The magnetic field sensor can preferably 100 a probe position unit which is designed to include a position and / or an orientation of the optical probe 4th to vary. In particular, the magnetic field sensor 100 based on the determined beam path of the test beam TS control the probe position unit to perform a position calibration of the optical probe 4th or a calibration / adaptation of the beam path of the test beam TS to enable.

The optical detector 3 can preferably be designed a polarization of the transmission of the test beam TS through the atomic vapor 2 to eat. The magnetic field sensor 100 can preferably have a probe polarization unit which is designed to polarize the test beam TS to vary. In particular, the magnetic field sensor 100 based on the measured polarization of the test beam TS control the probe polarization unit to carry out a polarization calibration of the optical probe 4th to enable.

The optical detector 3 can preferably be designed an intensity of the transmission of the test beam TS through the atomic vapor 2 to eat. The magnetic field sensor 100 can preferably have a probe intensity unit which is designed to indicate an intensity of the test beam TS to vary. In particular, the magnetic field sensor 100 based on the measured intensity of the test beam TS control the probe intensity unit to carry out a polarization calibration of the optical probe 4th to enable.

The sensor device can furthermore comprise an optical polarization signal detector, the optical polarization signal detector being designed to transmit the polarization signal PS through the atomic vapor 2 or a physical quantity of the transmission of the polarization signal PS through the atomic vapor 2 to eat.

The optical polarization signal detector can preferably be designed for a position of the transmission of the polarization signal PS through the atomic vapor 2 at which the transmission of the polarization signal PS through the atomic vapor 2 meets the optical polarization signal detector to determine. The magnetic field sensor 100 can preferably be a position of the pump laser 5 determine or determine. Alternatively, the position of the pump laser 5 in the magnetic field sensor 100 be saved. In particular, the magnetic field sensor 100 based on the position of the pump laser 5 and the position of the transmission of the polarization signal PS through the atomic vapor 2 at which the transmission of the polarization signal PS through the atomic vapor 2 hits the optical polarization signal detector, a beam path of the polarization signal PS determine. The magnetic field sensor can preferably 100 comprise a pump laser position unit which is designed to include a position and / or an orientation of the pump laser 5 to vary. In particular, the magnetic field sensor 100 based on the determined beam path of the polarization signal PS control the pump laser position unit to perform a position calibration of the pump laser 5 or a calibration / adaptation of the beam path of the polarization signal PS to enable.

The optical polarization signal detector can preferably be designed for a polarization of the transmission of the polarization signal PS through the atomic vapor 2 to eat. The magnetic field sensor 100 can preferably have a pump laser polarization unit which is designed to polarize the polarization signal PS to vary. In particular, the magnetic field sensor 100 based on the measured polarization of the polarization signal PS control the pump laser polarization unit in order to carry out a polarization calibration of the pump laser 5 to enable.

The optical polarization signal detector can preferably be designed to measure an intensity of the transmission of the polarization signal PS through the atomic vapor 2 to eat. The magnetic field sensor 100 can preferably have a pump laser intensity unit which is designed to provide an intensity of the polarization signal PS to vary. In particular, the magnetic field sensor 100 based on the measured intensity of the polarization signal PS control the pump laser intensity unit in order to carry out a polarization calibration of the pump laser 5 to enable.

The sensor device can furthermore comprise an optical kick pulse detector, the optical kick pulse detector being designed to transmit an optical kick pulse KP through the atomic vapor 2 or a physical quantity of the transmission of the optical kick pulse KP through the atomic vapor 2 to eat.

The optical kick pulse detector can preferably be designed for a position of the transmission of the optical kick pulse KP through the atomic vapor 2 at which the transmission of the optical kick pulse KP through the atomic vapor 2 hits the optical kick pulse detector to determine. The magnetic field sensor 100 can preferably be a position of the kick laser 6th determine or determine. Alternatively, the position of the kick laser 6th in the magnetic field sensor 100 be saved. In particular, the magnetic field sensor 100 based on the position of the kick laser 6th and the position of the transmission of the optical kick pulse KP through the atomic vapor 2 at which the transmission of the optical kick pulse KP through the atomic vapor 2 hits the optical kick pulse detector, a beam path of the optical kick pulse KP determine. The magnetic field sensor can preferably 100 a kick laser position unit which is designed to include a position and / or an orientation of the kick laser 6th to vary. In particular, the magnetic field sensor 100 based on the determined beam path of the optical kick pulse KP control the kick laser position unit in order to calibrate the position of the kick laser 6th or a calibration / adaptation of the beam path of the optical kick pulse KP to enable.

The optical kick pulse detector can preferably be designed to polarize the transmission of the optical kick pulse KP through the atomic vapor 2 to eat.

The magnetic field sensor 100 can preferably have a kick laser polarization unit which is designed to polarize the optical kick pulse KP to vary. In particular, the magnetic field sensor 100 based on the measured polarization of the optical kick pulse KP control the kick laser polarization unit to carry out a polarization calibration of the kick laser 6th to enable.

The optical kick pulse detector can preferably be designed to indicate an intensity of the transmission of the optical kick pulse KP through the atomic vapor 2 to eat. The magnetic field sensor 100 can preferably have a kick laser intensity unit which is designed to provide an intensity of the optical kick pulse KP to vary. In particular, the magnetic field sensor 100 based on the measured intensity of the optical kick pulse KP Control the kick laser intensity unit to calibrate the polarization of the kick laser 6th to enable.

In particular, a test volume can be defined, the test volume having all spins of the spin system or atoms of the atomic vapor 2 includes which with the one optical test beam TS interact by spin-photon interaction or electron-photon interaction. The magnetic field sensor 100 is preferably designed here so that an intersection between the polarization volume, the test volume and the chaos volume is at least one element or one spin or one atom of atomic vapor 2 includes. In particular, the magnetic field sensor 100 be designed, the beam path of the test beam TS and / or the beam path of the polarization signal PS and / or the beam path of the at least one optical kick pulse KP to be calibrated in such a way that an intersection between the polarization volume, the test volume and the chaos volume is at least one element or one spin or one atom of atomic vapor 2 includes.

The at least one kick laser 6th is preferably configured to use the optical kick pulse KP parallel to the optical test beam TS to emit. Alternatively, there is at least one kick laser 6th configured so that a path of the test beam TS and a distance of the at least one optical kick pulse KP cross. Here are the test beam TS and / or the at least one optical kick pulse KP preferably aligned in such a way that an interaction, in particular based on the Faraday effect, between the test beam TS and / or the at least one optical kick pulse KP with the spins of the spin system or with the atoms of atomic vapor 2 is effected or occurs. The polarization of the spins of the spin system or of the atoms of the atomic vapor can preferably 2 before the measurement or the measuring process of a magnetic field B. aligned to ensure such interaction.

Preferably forms an alignment direction or alignment of the pump laser 5 or an alignment of the at least one polarization signal PS an acute or right angle with the external magnetic field B. or with the magnetic field to be measured B. . Preferably forms a polarization direction or alignment of the kick laser 6th or an alignment of the at least one optical kick pulse KP an acute or right angle with the external magnetic field B. or with the magnetic field to be measured B. .

In particular, the magnetic field sensor 100 be designed so that the kick laser 6th or the optical manipulation device configured, the test beam TS to emit. In other words, the magnetic field sensor comprises 100 in particular, no separate optical probe 4th , with the kick laser instead 6th is designed to give at least one visual kick KP and the test beam TS to emit. Thus, the kick laser 6th or the optical manipulation device takes on the role of the optical probe 4th take over or additionally as an optical probe 4th be trained. The kick laser is for this 6th configured to emit laser light with controllable, variable intensity. The kick laser can preferably 6th in this case also be configured to have at least one first optical kick pulse KP and at least one last optical kick pulse KP to emit, the optical detector 3 the last optical kick pulse KP at least partially measures to an external magnetic field B. to eat.

The magnetic field sensor 100 preferably comprises at least one magnetic field device 7th , which is designed to generate magnetic field pulses in the measuring cell 1 to create. The magnetic field device 7th comprise at least one magnetic field coil which surrounds the measuring cell 1 is arranged. In particular, the magnetic field device 7th designed the initial state AZ of the spin system or the spins of the spin system to rotate or rotate and / or thus to align along a desired direction. In particular, the magnetic field device 7th designed, the initial state polarized by the optical manipulation device AZ of the spin system or the spins of the spin system to rotate or rotate and / or thus to align along a desired direction. In particular, the magnetic field device 7th be designed the initial state AZ of the spin system or the spins of the spin system to rotate or rotate, so that the polarization direction of the at least one polarization signal PS essentially orthogonal to the emission direction of the at least one optical kick pulse KP is.

The magnetic field sensor 100 can preferably be a heating device 8th have, wherein the heating device 8th is designed, the measuring cell 1 to heat and thus the atomic vapor 2 keep at a predetermined temperature. The heating device 8th comprise at least one heating element, for example heating coils and / or Peltier elements and / or electromagnetic heating elements. For this purpose, the heating device can furthermore comprise at least one thermometer element and at least one temperature control element. The at least one thermometer element is designed here to be a temperature of the atomic vapor 2 or an object, which in a known way thermally with the atomic vapor 2 is coupled and from its temperature the temperature of the atomic vapor 2 can be determined, measure and thus the temperature of the atomic vapor 2 to determine. The determined temperature of the atomic vapor 2 can be transmitted to the at least one temperature control element, which is designed based on the determined temperature of the atomic vapor 2 to control the at least one heating element in such a way that the temperature of the atomic vapor 2 corresponds to a predetermined value.

mit dem ein Magnetfeld pro 1 cm³ Volumen des Atomdampfes gemessen werden kann, (a) für eine Polarisationsmessung auf Basis von periodischen optischen Kickpulsen (Werte durch eine punktiert-gestrichelte Linie gekennzeichnet) und für (b) eine Magnetfeldmessung auf Basis einer Referenzmethode (Werte durch eine gestrichelte Linie gekennzeichnet) dargestellt und kontrastiert. Die X-Achse repräsentiert hierbei die Messzeit T_Mess , welche hierbei in diskreten Schritten angegeben ist, welche der Zahl der emittierten optischen Kickpulse der Länge τ entsprechen. 3 shows an example of a graphic representation of the measurement accuracy for various magnetic field measurement methods based on example 1. In particular, the minimum error or the measurement accuracy (standard deviation) is δB pro $\sqrt{Hz,}$

with which a magnetic field per 1 cm ³ volume of atomic vapor can be measured, (a) for a polarization measurement based on periodic optical kick pulses (values indicated by a dotted-dashed line) and for (b) a magnetic field measurement based on a reference method (values indicated by a dashed line) and contrasted. The X-axis represents the measurement time T _Mess , which is specified in discrete steps which correspond to the number of emitted optical kick pulses of length τ.

Hierbei ist N' die Anzahl der Atome des Atomdampfes, welche bei einer Dichte von 2*10¹⁰ Atomen/cm³ in 1 cm³ enthalten sind, N'= 2*10¹⁰ , und F_t=F/T_Mess die zeitskalierte Fisher-Information ist, wobei F die Fisher-Information und T_Mess eine Dauer der Messdynamik repräsentiert. Aus der Simulation ergeben sich die jeweiligen Minimalwerte für die Standardabweichung δB für (a) δB_a = 3.68*10^-18, (b) δB_b=1.15*10^-17. Die jeweiligen Minimalwerte sind in 3 durch horizontale bzw. der X-Achse parallele Balken gekennzeichnet. Für einen Vergleich der Fälle (a) und (b) ist der minimale Fehler um etwa 68% gegenüber der Referenzmethode reduziert.The measurement accuracy ΔB was calculated on the basis of Fisher information: $$\Delta \mathrm{B.}=\frac{1}{\sqrt{N\text{'}{\mathrm{F.}}_i}}$$

Here N 'is the number of atoms of atomic vapor which are contained in 1 cm ^{3 at a density of 2 * 10 10} atoms / cm ³ , N' = 2 * 10 ¹⁰ , and F _t = F / T _{Mess is} the time-scaled Fisher -Information, where F represents Fisher information and T _Mess a duration of the measurement dynamics. The respective minimum values for the standard deviation δB for (a) δB _a = 3.68 * 10 ^-18 , (b) δB _b = 1.15 * 10 ^-17 result from the simulation. The respective minimum values are in 3 marked by horizontal bars or bars parallel to the X-axis. To compare cases (a) and (b), the minimal error is reduced by around 68% compared to the reference method.

In the context of this description, the term “essentially” is to be understood as comprehensively minor manufacturing and environmental deviations.

The invention is not limited to the above in the description and in the drawings

List of reference symbols

100

Magnetic field sensor

1

Measuring cell

2

Atomic vapor

3

Optical detector

4th

Optical probe

5

Pump laser

6th

Kick laser

7th

Magnetic field device

8th

Heating device

9

Signal divider

10A

First photodiode

10B

Second photodiode

11

Evaluation unit

B.

External or magnetic field to be measured

PS

Polarization signal

KP

Optical kick pulse

TS

Optical test beam

AZ

Initial state

EZ

Final state

R _z (α)

Precession

Claims (19)

Magnetic field sensor (100) for measuring a magnetic field (B), comprising: a measuring cell (1) which comprises an atomic vapor (2), the atomic vapor (2) having a spin system of spins of individual atoms; an optical manipulation device which is designed to polarize the spin system in an initial state (AZ) by emitting light and to establish a state of the spin during a measuring process of the magnetic field (B) by emitting at least one optical kick pulse (KP) Change system, wherein the at least one optical kick pulse (KP) generates chaotic dynamics of the spin system; and a sensor device comprising: - an optical probe (4) which is designed to emit an optical test beam (TS) through the atomic vapor (2), and - An optical detector (3) which is designed to measure a transmission of the optical test beam (TS) through the atomic vapor (2). Magnetic field sensor (100) according to one of the preceding claims, wherein the optical detector (3) is designed to measure the transmission of the test beam (TS) during the chaotic dynamics of the spin system. Magnetic field sensor (100) according to one of the preceding claims, wherein the optical manipulation device comprises at least one pump laser (5) which is designed to polarize the spin system in an initial state (AZ) by emitting light. Magnetic field sensor (100) Claim 3 wherein the at least one pump laser (5) is configured to emit circularly polarized light. Magnetic field sensor (100) according to one of the preceding claims, wherein the optical manipulation device comprises at least one kick laser (6) which is designed to emit the at least one optical kick pulse (KP), or the optical probe (4) as at least one Kick laser (6) is designed and is also designed to emit the at least one optical kick pulse (KP). Magnetic field sensor (100) Claim 5 , wherein the at least one kick laser (6) is configured to emit the optical kick pulse (KP) parallel to the optical test beam (TS). Magnetic field sensor (100) Claim 5 or 6th , wherein the at least one kick laser (6) is configured to emit linearly polarized light. Magnetic field sensor (100) according to one of the preceding claims, wherein the magnetic field sensor (100) comprises at least one magnetic field device (7) which is designed to generate magnetic field pulses in the measuring cell (1). Magnetic field sensor (100) according to one of the preceding claims, wherein the optical manipulation device is designed to maintain the chaotic dynamics of the spin system by emitting at least one optical kick pulse, wherein the optical manipulation device is designed to receive the at least one optical kick pulse to emit at essentially periodic intervals. Magnetic field sensor (100) according to one of the preceding claims, wherein an intensity of the optical kick pulse (KP) has a rectangular function or a triangular function and / or a non-linear function. Magnetic field sensor (100) according to one of the preceding claims, wherein the optical detector (3) is designed to measure an intensity and / or a polarization of the transmission of the test beam (TS). Magnetic field sensor (100) according to one of the preceding claims, wherein the atomic vapor (2) ^{comprises alkali atoms, preferably 133} Cs atoms. Magnetic field sensor (100) according to one of the preceding claims, wherein I the atomic vapor (2) comprises at least one. Magnetic field sensor (100) according to one of the preceding claims, wherein the atomic vapor (2) has a density of at least about 10 ⁴ atoms / cm ³ , preferably of at least about 10 ⁹ atoms / cm ³ , and / or of a maximum of about 10 ¹⁵ atoms / cm ³ , preferably of a maximum of about 10 ¹¹ atoms / cm ³ . Magnetic field sensor (100) according to one of the preceding claims, wherein the initial state (AZ) is a hyperfine ground state of the spin system. Magnetic field sensor (100) according to one of the preceding claims, wherein the optical manipulation device is designed to generate the initial state (AZ) by means of a circularly polarized light field. A method for measuring a magnetic field (B), comprising: Providing a measuring cell (1) which comprises an atomic vapor (2), the atomic vapor (2) having a spin system of spins of individual atoms; Polarizing the spin system in an initial state (AZ) by means of an optical manipulation device; Generating chaotic dynamics of the spin system by outputting at least one optical kick pulse (KP) from the manipulation device to the spin system; Generating an optical test beam (TS) from an optical probe (4) through the atomic vapor (2); and Measuring a transmission of the optical test beam (TS) through the atomic vapor (2) from an optical detector (3) which receives the optical test beam (TS). Procedure for measuring a magnetic field (B) according to Claim 17 , further comprising: rotating the initial state (AZ) after polarizing the spin system and before generating the chaotic dynamics by generating at least one magnetic field pulse by at least one magnetic field device (7). Method for measuring a magnetic field (B) according to one of the Claims 17 to 18th , further comprising: rotating a state of the spin system, after generating the optical test beam (TS) and before measuring the transmission, by generating at least one magnetic field pulse by at least one magnetic field device (7).

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