Patent Description:
Atom-based quantum effects may be used in developing quantum sensors for various physical quantities, as is known in the art.

Detection of microwave signals based on quantum sensors often involves a read-out in an optical manner. A common setup for reading out the state of quantum sensors such as atomic vapor cells involves analyzing the transmitted power of a laser beam. Quantum sensors such as Nitrogen-vacancy (NV) diamonds are typically read out by analyzing their emitted fluorescence light.

The light pattern emanating from the quantum sensor depends on the frequency components of the analyzed microwave signal, and may be imaged with a digital camera and further transformed to identify said frequency components. For example, <CIT> discloses an implementation of a measurement system for analysis of RF signals being based on a digital camera and a subsequent transformation to identify frequency components.

According to a conventional implementation, the transformation on a CPU, DSP or FPGA consumes time and electrical energy.

The present disclosure therefore strives to improve an RF signal analysis of the background art. The objective is achieved by the embodiments as defined by the appended independent claims. Preferred embodiments are set forth in the dependent claims and in the following description and drawings.

A first aspect of the present disclosure, as defined in claim <NUM>, relates to a measurement system for analyzing an RF signal.

The system comprises a sensing medium, including at least one constituent being pumpable to an initial energy state, and being excitable from the initial energy state to a higher energy state by exposure to an electric and/or magnetic field. The system further comprises an optical pump configured to pump the at least one constituent of the medium to the initial energy state. The system further comprises an antenna configured to expose the medium to an electromagnetic field of the RF signal. The system further comprises an optical processor configured to apply a linear transformation to light emanating from the pumped medium. The system further comprises an optical detector configured to detect an optical property of the transformed light.

The system may further comprise a field generator configured to expose the medium to a static electric or magnetic field, a strength of which defines an absorption spectrum of the medium.

The strength of the generated field may have a gradient along a spatial dimension of the medium. The field generator may comprise a permanent magnet.

The optical processor comprises a trained artificial neural network, ANN, being configured to apply the linear transformation to the light emanating from the pumped medium.

The trained ANN comprises a number of diffractive layers being arranged in series for traversal by the light emanating from the pumped medium.

The diffractive layers may be established by supervised learning with labelled training data, and additive manufacture.

The labelling of the training data may take into account one or more of: a desired output of the linear transformation; a focusing of the transformed light to the optical detector; calibration; and error correction.

The medium may comprise an alkali metal enclosed in an atomic vapor cell; and the at least one constituent of the medium may comprise atoms or ions in a buffer gas. The light emanating from the pumped medium may comprise a pump light transmission through the medium having a cross-sectional intensity distribution depending on a frequency of the electromagnetic field of the RF signal.

The medium may comprise a Nitrogen vacancy, NV, diamond; and the at least one constituent of the medium may comprise point defects. The light emanating from the pumped medium may comprise a light emission of the medium having a directional intensity distribution depending on the frequency of the electromagnetic field of the RF signal. The system may further comprise an optical lens configured to collimate the light emanating from the pumped medium onto the optical processor.

The pump may comprise at least one coherent optical light source.

The detector may comprise at least one charge-coupled device, CCD, chip or CMOS chip etc., extending across a cross-section of the transformed light; and the detected optical property may comprise a cross-sectional intensity distribution of the transformed light.

A second aspect of the present disclosure relates to a method of analyzing an RF signal. The method, which is defined in claim <NUM>, comprises pumping at least one constituent of a sensing medium to an initial energy state. The at least one constituent is further excitable from the initial energy state to a higher energy state by exposure to an electric and/or magnetic field. The method further comprises exposing the medium to an electromagnetic field of the RF signal. The method further comprises applying a linear transformation to light emanating from the pumped medium. The method further comprises detecting an optical property of the transformed light.

The present disclosure provides a measurement system for analyzing RF/microwave signals which optically pre-processes the light pattern emanating from the pumped medium before it is imaged by a camera. This scheme does not consume electrical power at runtime (with regard to the optical processor), works at the speed of light, and requires no extra conversions.

It is possible to encode a trained neural network in such an optical processor ("AI lens"). The neural network may be trained to also perform tasks such as focusing the image to the optical detector, e.g. the afore-mentioned camera, or additional calibration, or error correction, yielding a multi-purpose AI lens that performs multiple tasks at once.

The technical effects and advantages described above in relation with the measurement system of the first aspect equally apply to the method of the second aspect having corresponding features.

The above-described aspects and implementations will now be explained with reference to the accompanying drawings, in which the same or similar reference numerals designate the same or similar elements.

The features of these aspects and implementations may be combined with each other unless specifically stated otherwise.

The drawings are to be regarded as being schematic representations, and elements illustrated in the drawings are not necessarily shown to scale. Rather, the various elements are represented such that their function and general purpose become apparent to those skilled in the art.

<FIG> illustrates a measurement system <NUM> in accordance with a first implementation for analyzing an RF signal.

The system <NUM> comprises a sensing medium <NUM>, including at least one constituent being pumpable to an initial energy state, and being excitable from the initial energy state to a higher energy state by exposure to an electric and/or magnetic field.

In particular, the medium <NUM> may comprise an alkali metal - such as Rubidium - enclosed in an atomic vapor cell <NUM>, and the at least one constituent of the medium <NUM> may comprise atoms or ions of the alkali metal in a buffer gas.

The system <NUM> further comprises an optical pump <NUM> configured to pump the at least one constituent of the medium <NUM> to the initial energy state.

The pump <NUM> may comprise at least one coherent optical light source.

In particular, the pump <NUM> may comprise a single coherent optical light source for pumping and readout of the medium <NUM>. Alternatively, the pump <NUM> may comprise a first coherent optical light source for pumping and a second coherent optical light source for readout. For example, the respective coherent optical light source may comprise a laser.

The system <NUM> further comprises an antenna <NUM> configured to expose the medium <NUM> to an electromagnetic field of the RF signal.

In particular, the antenna <NUM> may comprise a waveguide such as a metallic wire (shown in <FIG> and <FIG>) around which a near field may evolve responsive to the RF signal. Alternatively, the antenna <NUM> may comprise a microwave antenna (not shown) such as a reflector antenna, horn antenna, or the like. Using a single antenna ensures that a time-dependency of the RF signal under analysis is consistent across all regions of the cell.

The system <NUM> further comprises an optical processor <NUM> configured to apply a linear transformation to light emanating from the pumped medium <NUM>. That is, the optical processor <NUM> is an optical element configured to manipulate a spatial distribution of the light.

In the implementation of <FIG>, the light emanating from the pumped medium <NUM> may comprise a pump light transmission through the medium <NUM> having a cross-sectional intensity distribution depending on a frequency of the electromagnetic field of the RF signal.

The optical processor <NUM> may comprise a trained artificial neural network, ANN <NUM>, being configured to apply the linear transformation to the light emanating from the pumped medium <NUM>.

An example of such an optical processor <NUM> is described in "<NPL>).

The trained ANN <NUM> may comprise a number of diffractive layers <NUM> being arranged in series for traversal by the light emanating from the pumped medium <NUM>. The diffractive layers <NUM> are microstructured diffraction surfaces which implement a linear transformation on the input light.

The diffractive layers <NUM> may be established by supervised learning with labelled training data, and additive manufacture, such as 3D printing.

The labelling of the training data may take into account one or more of: a desired output of the linear transformation; a focusing of the transformed light to an optical detector <NUM>; calibration; and error correction.

The system <NUM> further comprises the optical detector <NUM> configured to detect an optical property of the transformed light.

The detector <NUM> may comprise at least one charge-coupled device, CCD, chip extending across a cross-section of the transformed light. For example, if the detector <NUM> cannot measure continuously, it is possible to use two camera chips taking turns. The detected optical property may comprise a cross-sectional intensity distribution of the transformed light.

The system <NUM> may further comprise a field generator <NUM> configured to expose the medium <NUM> to a static electric or magnetic field. A strength of the generated field may define an absorption spectrum of the medium <NUM>.

In particular, the strength of the generated field may have a gradient along a spatial dimension X of the medium <NUM>. In <FIG>, said spatial dimension X is indicated by an arrow pointing upwardly along the medium <NUM>.

In particular, the field generator <NUM> may comprise a permanent magnet. For example, <FIG> shows a pair of oppositely aligned permanent magnets <NUM> whose respective magnetic fields tend to cancel each other out halfway of their spacing. As a result, the strength of the generated magnetic field has a gradient along the spatial dimension X of the medium <NUM>.

A presence of such an inhomogeneous magnetic field may cause Zeeman splitting, which ensures availability of atoms, ions or point defects in an initial state for each frequency in a desired frequency range, which may be included in a microwave frequency range ranging between <NUM> and <NUM>, respectively.

Zeeman splitting may refer to splitting of a spectral line, such as the initial state, into several components in the presence of a static magnetic field. Stark splitting, the electric-field analogue of Zeeman splitting, may refer to splitting of a spectral line into several components in the presence of a static electric field.

<FIG> illustrates a measurement system <NUM> in accordance with a second implementation for analyzing an RF signal.

In the alternative implementation of <FIG>, the medium <NUM> may comprise a Nitrogen vacancy, NV, diamond, and the at least one constituent of the medium <NUM> may comprise point defects. In this case, the light emanating from the pumped medium <NUM> may comprise a - fluorescent - light emission of the medium <NUM> having a directional intensity distribution depending on the frequency of the electromagnetic field of the RF signal.

In other words, the light emission may be divergent. As such, the system <NUM> may further comprise an optical lens <NUM> configured to collimate the light emanating from the pumped medium <NUM> onto the optical processor <NUM>.

All other elements of <FIG> correspond to those already explained in connection with <FIG> and having same reference numerals.

<FIG> illustrate expected light patterns at interfaces A-A' of <FIG> and <FIG>.

<FIG> shows no RF signal at all (f = <NUM>).

<FIG> shows an expected multi-component light pattern resulting from a first exemplary RF frequency component (f = <NUM>).

<FIG> shows an expected multi-component light pattern resulting from a second exemplary RF frequency component (f = <NUM>).

The multi-component patterns of <FIG> complicate an identification of the analyzed frequency components, and this would become even more difficult when analyzing multiple frequency components.

After optical processing (i.e., transformation) of the expected light patterns of <FIG>, the detector images should ideally correspond to the light patterns of <FIG>.

<FIG> illustrate desired light patterns at interfaces B-B' of <FIG> and <FIG>.

<FIG> shows no RF signal (f = <NUM>), owing to a lack of frequency content.

<FIG> shows a desired single-component light pattern resulting from the first exemplary RF signal (f = <NUM>).

<FIG> shows a desired single-component light pattern resulting from the second exemplary RF signal (f = <NUM>).

<FIG> represent example light patterns that may be used as labelled training data for supervised learning. More specifically, this may involve applying <FIG> and similar light patterns one after another to an input layer of the ANN <NUM>, obtaining resulting output light patterns at an output layer of the ANN <NUM>, and performing a backpropagation (or similar) algorithm to train the ANN <NUM> based on discrepancies between pairs of output light patterns and desired light patterns.

<FIG> illustrates a flow chart of a method <NUM> in accordance with the present disclosure for analyzing an RF signal.

The method <NUM> comprises pumping <NUM> at least one constituent of a sensing medium <NUM> to an initial energy state. The at least one constituent is further excitable from the initial energy state to a higher energy state by exposure to an electric and/or magnetic field.

The method <NUM> further comprises exposing <NUM> the medium <NUM> to an electromagnetic field of the RF signal.

The method <NUM> further comprises applying <NUM> a linear transformation to light emanating from the pumped medium <NUM>.

Claim 1:
A measurement system (<NUM>) for analyzing an RF signal, comprising
- a sensing medium (<NUM>), including at least one constituent
- being pumpable to an initial energy state, and
- being excitable from the initial energy state to a higher energy state by exposure to an electric and/or magnetic field;
- an optical pump (<NUM>) configured to pump the at least one constituent of the sensing medium (<NUM>) to the initial energy state;
- an antenna (<NUM>) configured to expose the sensing medium (<NUM>) to an electromagnetic field of the RF signal in order to excite it;
wherein light emanating from the pumped sensing medium (<NUM>) has a spatial distribution, which depends on the frequency of the RF signal;
the measurement system (<NUM>) further comprising:
- an optical processor (<NUM>) comprising a trained diffractive deep neural network being an artificial neural network, ANN (<NUM>), that comprises a number of diffractive layers (<NUM>) being arranged in series for traversal by the light emanating from the pumped medium (<NUM>), and that is configured to manipulate the spatial distribution of the light such as to apply a linear transformation to the light emanating from the pumped sensing medium (<NUM>),
wherein the ANN (<NUM>) is trained based on discrepancies between pairs of output light patterns and desired light patterns; and
- an optical detector (<NUM>) configured to detect an optical property of the transformed light.