Systems and methods for entanglement assisted sensing and radars with phase conjugation on idler photons

Abstract

A system and method are provided for entanglement assisted quantum sensing. An entangled source generates entangle photon pairs that include a signal photon and an idler photon. The signal photon is modulated and transmitted to a target. In the monostatic configuration, the idler photon stays at the radar, where the idler photon passes through a quantum memory or delay line and an optical phase-conjugate module. The radar return signal includes signal photons that have interacted with the target (e.g., reflected from the target). The received signal photons are detected using balanced homodyne detection by beating the received signal photons against the phase-conjugate idler photons, which function as a local oscillator. The target is detected using a cross-correlation between the electrical signal from the homodyne balanced detector and the modulation pattern used to modulate the signal photons.

Description

085067-817582 (UA24-038) SYSTEMS AND METHODS FOR ENTANGLEMENT ASSISTED SENSING AND RADARS WITH PHASE CONJUGATION ON IDLER PHOTONS CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This is a PCT application that claims priority to U.S. Provisional Application No.63 / 589,288 filed on October 10, 2023, which is expressly incorporated by reference herein in its entirety. FIELD

[0002] The present disclosure generally relates to the use of an entanglement assisted receiverfor performing an optical phase-conjugation process on received photons BACKGROUND

[0003] Entanglement represents an extremely important quantum information processing(QIP) feature. Among others, entanglement enables: (i) quantum sensors with sensitivity better than the standard quantum limit, (ii) quantum radars with high detection probability in low signal-to-noise ratio regime, (iii) communications with spectral efficiency higher than the Shannon limit, (iv) secure communication with security guaranteed by the QIP theorems, (v) distributed quantum sensing, and (vi) secure distributed quantum computing, just to name few.

[0004] To exploit unique properties of entanglement, quantum communication links areestablished to distribute entanglement towards the remote nodes. To distribute entanglement fiber-optics based links are typically used. To enable wider area and / or global coverage, entanglement can be distributed with the help of satellite-to-ground links; however, this approach suffers from long propagation delays. Terrestrial free-space optical links can also be used to distribute entanglement, even in the strong turbulence regime.

[0005] It is with these observations in mind, among others, that various aspects of the presentdisclosure were conceived and developed. SUMMARY

[0006] The challenges presented by making a radar both covert and practical are addressed bythe proposed systems and methods.085067-817582 (UA24-038)

[0007] In some aspects, the techniques described herein relate to a system including: atransmitter that includes: an entangled source that generates a first optical field and a second optical field in a second quantum state, and a combination of the first optical field and the second optical field including a quantum entangled state, and output optics that transmit the first optical field to provide a transmitted field; an optical memory that stores the second optical field; a receiver that includes: input optics that receive the transmitted field to provide a received field, and a balanced detector that receives the received field at a first port and receives a phase-conjugated field at a second port to generate an electrical signal; and a phase- conjugate component arranged in an optical path of the second optical field between the entangled source and the balanced detector, the phase-conjugate component applying phase conjugation to the second optical field to generate the phase-conjugated field.

[0008] In some aspects, the techniques described herein relate to a method including:generating, by an entangled source of a transmitter, a first optical field and a second optical field in a second quantum state, wherein a combination of the first optical field and the second optical field includes a quantum entangled state; using a phase-conjugate component to apply phase conjugation to the second optical field to generate a phase-conjugated field; storing, in an optical memory, at least one of the second optical field or the phase-conjugated field; transmitting, from the transmitter, the first optical field to provide a transmitted field; receiving the transmitted field at a receiver to provide a received field, and inputting the received field at a first port of a balanced detector and the phase-conjugated field at a second port of the balanced detector to generate an electrical signal.

[0009] In some aspects, the techniques described herein relate to a system including: anentangled photon pair generation engine that generates an entangled photon pair; a periodically poled lithium niobate waveguide that receives a pump photon and generates, based on the pump photon, a signal photon and an idler photon; an optical phase-conjugation module configured to receive the idler photon; a quantum memory; a homodyne balanced detector; one or more processors; and a computer-readable storage medium storing instructions which, when executed by the one or more processors, cause the one or more processors to perform operations including: generating, by the optical phase-conjugation module and based on the idler photon, a phase-conjugated idler photon; transmitting the signal photon to a target to obtain a reflected probe signal photon; storing the phase-conjugated idler photon in the quantum memory;085067-817582 (UA24-038) receiving, at the homodyne balanced detector, the reflected probe signal photon and the phase- conjugated idler photon; and detecting, at the homodyne balanced detector, one or more of an amplitude variation and a phase variation. BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0010] In order to describe the manner in which the above-recited and other advantages andfeatures of the disclosure can be obtained, a more particular description of the principles briefly described above will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. Understanding that these drawings depict only exemplary embodiments of the disclosure and are not therefore to be considered to be limiting of its scope, the principles herein are described and explained with additional specificity and detail through the use of the accompanying drawings in which:

[0011] FIG. 1 illustrates a monostatic entanglement assisted (EA) radar, in accordance withsome embodiments.

[0012] FIG. 2 illustrates an entanglement assisted receiver performing the optical phaseconjugation on receiver side signal photons.

[0013] FIG. 3 illustrates C-band pump-based multiwavelength entangled-photon source, inaccordance with some embodiments.

[0014] FIG. 4 illustrates an entanglement assisted module performing phase-conjugation onidler photons, in accordance with some embodiments.

[0015] FIG. 5 illustrates aa block diagram for a first implementation of a monostatic / bistaticentanglement assisted quantum radar, in accordance with some embodiments.

[0016] FIG. 6 illustrates a flow diagram of a method for implementing an entanglementassisted quantum radar, in accordance with some embodiments.

[0017] FIG. 7 illustrates a block diagram for a second implementation of a monostaticbroadband incoherent light radar, in accordance with some embodiments.

[0018] FIG. 8A illustrates a plot of target detection probabilities for different atmosphericturbulence realizations, in accordance with some embodiments.

[0019] FIG. 8B illustrates a histogram plot for a received power distribution in strongturbulence, in accordance with some embodiments.085067-817582 (UA24-038)

[0020] FIG. 8C illustrates a histogram plot for a received power distribution in mediumturbulence, in accordance with some embodiments.

[0021] FIG. 9 illustrates a plot of target detection probabilities for an entanglement assistedquantum radar with and without using adaptive optics, in accordance with some embodiments.

[0022] FIG. 10 illustrates a C-band pump-based multiwavelength entangled-photon source, inaccordance with some embodiments.

[0023] FIG. 11 illustrates a plot of coincidence count measurement results for 1550nm-1570nm entangled photon pairs in a back-to-back configuration, in accordance with some embodiments.

[0024] FIG. 12A illustrates a block diagram of a reflective architecture for a quantum sensor,in accordance with some embodiments.

[0025] FIG. 12B illustrates a block diagram of a transmissive architecture for a quantumsensor, in accordance with some embodiments.

[0026] FIG. 13 illustrates a block diagram of a computing device, in accordance with someembodiments. DESCRIPTION OF EXAMPLE EMBODIMENTS

[0027] Various embodiments of the disclosure are discussed in detail below. While specificimplementations are discussed, it should be understood that this is done for illustration purposes only. A person skilled in the relevant art will recognize that other components and configurations may be used without parting from the spirit and scope of the disclosure.

[0028] Additional features and advantages of the disclosure will be set forth in the descriptionwhich follows, and in part will be obvious from the description, or can be learned by practice of the herein disclosed principles. The features and advantages of the disclosure can be realized and obtained by means of the instruments and combinations particularly pointed out in the appended claims. These and other features of the disclosure will become more fully apparent from the following description and appended claims, or can be learned by the practice of the principles set forth herein.

[0029] The disclosed technology addresses the need in the art for improved radar detection,which can be achieved using quantum entanglement.085067-817582 (UA24-038)

[0030] Entanglement assisted (EA) communication and sensing represent excellentalternatives to classical communication and sensing in particular in either low-brightness or high-attenuation regime and when the signal photons are buried in noise. In EA communication idler photons are stored in memory while the signal photons, carry information, are transmitted over lossy, noisy, and for communication over free-space optical (FSO) channels signal photons are also affected by the atmospheric turbulence and scattering effects. In optical phase conjugation (OPC)-based EA receiver, the OPC operation is performed on signal photons, which are severely affected by FSO channel impairments, with many signal photons being either absorbed or scattered by the FSO channel. Proposed herein is the concept of performing the OPC operation on bright idler photons instead. The OPC operation is performed using low- cost, C-band components including tunable laser, periodically polled lithium niobate (PPLN) waveguides, tunable filter, and WDM demultiplexer; and this implementation is suitable for the operation in strong atmospheric turbulence regime and beyond.

[0031] A similar approach is applied to implement the C-band devices-based entanglementsource. Both PPLN waveguides-based entanglement generation source and OPC module are operated at room temperature. Given that the idler photons are brighter compared to the signal photons transmitted over either FSO channel or fiber-optics channel, the OPC operation is much more efficient. Moreover, it can be done at various locations during the distribution of entanglement, including transmitting side, receiver side, or an intermediate location. In the OPC-based receiver for FSO communications, one needs to couple the signal photons to the single-mode fiber (SMF) before the OPC takes place, making the OPC process sensitive to the FSO-to-SMF coupling inefficiency. By performing the OPC on the idler photons instead, the OPC process is insensitive to poor coupling efficiency. In addition to being superior in terms of spectral efficiency compared to classical counterparts, in particular in highly lossy and noisy environment, the proposed EA scheme with the phase-conjugation on idler photons is superior to the corresponding scheme performing the phase-conjugation on signal photons in terms of receiver sensitivity making it an attractive option for radar and lidar applications. To validate the proposed concept, a terrestrial FSO testbed is developed. Experiments demonstrate that the target detection probability of the proposed entanglement assisted radar over turbulent FSO channel is significantly better than that of corresponding classical detection scheme.085067-817582 (UA24-038)

[0032] The entanglement assisted (EA) communication, utilizing the continuous variable (CV)degrees of freedom, has been studied for decades. Nevertheless, various practical implementation aspects appear to be still unsolved. To illustrate, some have shown by numerical analysis that employing a large enough number of the feedforward sum-frequency generation (FF-SFG) module sections in an EA receiver, it is possible to detect the signal in a very noisy and lossy environment. Unfortunately, FF-SFG module imperfections have not been studied, and complexity of implementation appears to be extremely high. Others propose to employ repetition coding applied over a large number of bosonic modes (>106). However, with such an approach full C- and L-bands, portions of S- and U-bands will be occupied, leaving no space for commercial telecom applications. Yet others propose an approach where limited number of bosonic modes is used in combination with a Gaussian modulation.

[0033] Contrary to the common practice to perform the OPC on signal photons at the receiverside, proposed herein is the idea to perform the OPC on the idler photons instead. In classical communications where there is not any correlation between the transmitted signal and LO signal, one can perform the OPC on transmitted signal. In EA communications, there exists the quantum phase-sensitive correlation between signal and idler photons that gives us the flexibility to choose to perform the OPC either on signal or idler photons. Given that idler photons are distributed by high-quality medium (such as fiber), they get preserved in the communication and sensing processes, while many signal photons get lost in atmospheric turbulent channel, so it makes sense to perform the OPC on idler photons instead.

[0034] The advantages of this approach can be summarized as follows. Firstly, instead ofperforming the OPC on signal photons that are transmitted over very lossy and noisy medium, with many signal photons being absorbed or scattered by the channel, wherein the signal photons reaching the receive side are extremely weak and buried in noise, the disclosed system performs the OPC on bright idler photons, making this process very efficient and reliable. Secondly, given that the idler photons need to be distributed over low-loss links to the receiver where they are stored in quantum memory until needed, in principle the system can perform the OPC on idler photons at any point during distribution process, including transmit node, receive node, and any intermediate node, which gives a desired flexibility for quantum networking and quantum sensing applications. Thirdly, after the OPC on idler photons, the classical homodyne balanced detection receiver can be used as the EA receiver. Fourthly, the proposed OPC085067-817582 (UA24-038) module implementation is suitable for realization in photonic integrated circuit (PIC) technology. Fifthly, the EA capacity of the proposed scheme is higher than that of conventional EA scheme with OPC being performed on received signal photons.

[0035] To reduce the overall system cost, the system can perform the OPC on idler photonsusing widely available, low-cost telecom devices operating in the C-band (or near C-band, e.g., but not limited to L-band, E-band, O-band, U-band, and S-band) including tunable laser, periodically polled lithium niobate (PPLN) waveguides already used for fiber-optics communications, optical bandpass filters, and WDM demultiplexers. To implement the entangled source, the system uses a similar approach by employing the same set of fiber-optics devices.

[0036] FIG. 1 illustrates a concept for entanglement assisted (EA) radars with OPC on idlerphotons. FIG.1 illustrates a non-limiting example in which the EA radar concept is applied using monostatic radar configuration (i.e. both transmitter and receiver are placed on the same location). However, this concept is also applicable on the bistatic scenario.

[0037] According to certain non-limiting examples, an entangled source is used on transmitterside to generate quantum correlated signal photons (the probe signal) and idler photons serving the role of LO laser (local reference). The OPC is performed on idler photons and phase- conjugated photons are stored in quantum memory. In the absence of quantum memory, the tunable optical delay line (ODL) can be used instead. The signal photons are with the help of expanding telescope transmitted over noisy, lossy, and atmospheric turbulent channel towards the target. The reflected signal photons are collected by the compressing telescope and detected by the radar’s receiver, and quantum correlation between radar return and retained reference signal (phase-conjugated idler photons) is exploited on receive side to improve the receiver sensitivity.

[0038] FIG. 1 illustrates a non-limiting example of system 100 in which target 114 is detectedusing EA radar techniques in which entangled source 104 generates signal photons 106 and idler photons 108. Signal photons 106 can be modulated (optional) and then sent to expanding telescope 110. Expanding telescope 110 transmits signal photons 106 as a free-space optical (FSO) beam (e.g., transmitted beam 112) towards target 114. Return beam 116 from target 114 is collected by compressing telescope 118 and coupled into a multimode fiber (MMF), such as085067-817582 (UA24-038) multimode fiber 120, which guides the signal photons 106 in return beam 116 to entanglement assisted receiver 122.

[0039] Idler photons 108 are received at optical phase-conjugate module 124 to generateconjugate idler photons (e.g., phase-conjugated idler 126) via difference frequency mixing. Quantum memory 128 can be arranged before or after optical phase-conjugate module 124. Quantum memory 128 is used to match a time delay of signal photons 106 to reach entanglement assisted receiver 122.

[0040] Entanglement assisted receiver 122 mixes the received signal photons 106 with thephase-conjugated idler 126 to generate mixed light. The mixed light is detected using balanced homodyne detection in which phase-conjugated idler 126 functions as the local oscillator. As a result of the balanced homodyne detection, entanglement assisted receiver 122 generates electrical signal 130, which is analyzed by processor 132 to generate a detection result (e.g., result 134).

[0041] As illustrated in FIG. 1 the systems and methods disclosed herein perform phaseconjugation on the idler photons, whereas other EA systems for communications apply phase conjugation to the signal photons. As discussed below, performing phase conjugation on the idler photons provides not previously expected beneficial results. To demonstrate these unexpected beneficial results, the discussion below contrast the scenario using optical phase conjugation (OPC) on the signal photons with the systems and methods disclosed herein that use OPC on the idler photons. EA scheme using OPC on the signal photons

[0042] In certain entanglement assisted optical communications with OPC performed onreceived signal photons. EA continuous variable (CV) communication systems can be used with the classical communication, operated at room temperature, at rates that are higher than the Shannon channel capacity.

[0043] FIG. 2 illustration of the EA receiver performing the OPC on receiver signal photons.For derivations herein, the photodetector responsivity is set to R=1 A / W, without loss of generality.085067-817582 (UA24-038)

[0044] Each signal-idler pair is in fact a two-mode squeezed vacuum (TMSV) state, generatedby the spontaneous parametric down conversion (SPDC), which can be represented in the Fock basis as follows: Eq. (1) with the meanand idler creation operators denoted by The phase sensitive signal-idlercross-correlation coefficient, defined as , is used to describe the signal-idler entanglement. Clearly in sothat , which is . The TMSV state is a pure entangled zero-mean Gaussian state, which corresponding Wigner covariance matrix is described by: , Eq. (2)where 1 Pauli -matrix. The spontaneous parametric down-conversion (SPDC)-based entangled source is in fact a broadband source having i.i.d. signal-idler mode pairs, with being the phase- matching bandwidth andan interval of the measurement.

[0045] The Alice-to-Bob (the main) channel has been modelled as a single-mode thermallossy Bosonic channel model as follows [1]: it’s Eq. (3)where denotes the transmissivity of the Alice-to-Bob channel, and denotes the annihilation operator of a thermal (background) mode, wherein the corresponding mean photon number is .

[0046] To improve the bandwidth efficiency of repetition phase encoding scheme over largenumber of bosonic modes, some have proposed to apply the Gaussian modulation (GM) on single photon of the TMSV state, with the receiver illustrated in FIG. 2. Alice performs the GM085067-817582 (UA24-038) by generating the I and Q coordinates in RF domain and using them as the RF inputs to an electro-optical I / Q modulator, wherein Gaussian samples are properly scaled to account for the I / Q modulator insertion loss such that average number of transmitted signal photons per mode is equal to . The following covariance matrix between Alice and Bob can be derived:, Eq. (4)

[0047] The optical phase-conjugate (OPC) receiver performing the OPC on received signalphotons, shown in FIG.2, is very often used as the EA detector. In this receiver the optical parametric optical amplifier (OPA) is used to nonlinearly interreact the signal mode and the vacuum mode and obtain the following output at the idler.

[0048] By setting the OPA gain to , the output idler portsimply . By interacting the and idler-modes on a balanced beam splitter (BBS),balanced detection (BD) circuit, one can obtain the following BD photocurrent operator: Eq. (5)

[0049] Forfor theexpectation of the BDoperator: Eq. (6)wherein in Eq. (6) one can assume that vacuum- and idler-modes are mutually uncorrelated.

[0050] If one does not ignore the variance terms originating from the vacuum state in theOPC-based EA receiver shown in FIG.2, one can obtain the following expression for the BD photocurrent operator variance:085067-817582 (UA24-038) Eq. (7) OPCon in photonic integrated circuit (PIC) technology. By moving the OPA to the idler branch, one can get the flexibility to perform the OPC on the transmit side, receive side, or in the middle of the link (at an intermediate node in networking scenario). By ensuring that , where the signal photon brightness is much higher, the output at the idler the OPA willbe just phase-conjugated signal mode, given that contributions originating from vacuum state can be neglected in high-brightness regime. By placing the OPA on transmitter side, one can potentially integrate the OPC module with the spontaneous parametric down-conversion (SPDC) module on the same chip. Moreover, many commercial, classical homodyne coherent detection schemes can be used as the EA detectors.

[0052] Alternatively, similarly to fiber-optics communications, one can use periodically poledLiNbO3 (PPLN) waveguide to realize the phase-conjugation by the difference frequency generation (DFG), and corresponding quantum transmitter is provided in FIG.3.

[0053] The first PPLN waveguide is used to generate signal-idler photons’ pair through theSPDC process. The signal and idler photons are separated after the first PPLN waveguide. In second PPLN waveguide through the DFG the pump photon interacts with input signal mode to get the phase-conjugated photon at. The idler photon is distributed to Bob’s receiver by an optical fiber (serving as a. This signal mode is modulated by an electro-optical (E / O) modulator, implemented also using the LiNbO3 technology. Therefore, the proposed quantum transmitter is perfectly suited for the integration on the same chip based on the LiNbO3 technology. The E / O modulator can also be swapped with the OPC PPLN waveguide, and in this case the modulation will take place before the phase-conjugation.

[0054] Strong pump 308 feeds parametric down conversion PPLN (e.g., PDC PPLN 302) togenerate signal photons which are directed along a top branch to an electro-optic modulator (e.g., E / O modulator 306). E / O modulator 306 modulates the signal photons to generate modulated signal photons. On the bottom branch after strong pump 308, residual pump 310085067-817582 (UA24-038) together with the idler photons feed optical phase-conjugation PPLN (e.g. OPC PPLN 304) to generate phase-conjugated idler photons.

[0055] As an illustration, for the strong pump at nm, through the SPDC an idlerphoton at nm and a signal photon at nm are obtained. In thesecond (OPC) PPLN the idler photon interacts with the pump photon through DFG to get the phase-conjugated (PC) signal photon at nm, which is the same wavelength as the idler photon. EA scheme using OPC on the idler photons

[0056] Next is discussed the proposed EA scheme of performing optical phase conjugation(OPC) on the idler photons. FIG.4 illustrates an example of a scheme using OPC on the idler photons and a corresponding receiver. More particularly, FIG.4 illustrates an entanglement assisted receiver corresponding to EA transmitter implemented as a homodyne balanced detector with optical hybrid based on balanced beam splitter

[0057] By moving the OPC to the idler branch of the transmitter, one can use balanceddetection schemes devised for classical communications in EA detection, with one such scheme provided in FIG.4, where one can interact the phase-conjugated signal and idler modes directly on BBS. The BD photocurrent operator is now simply: , Eq. (8)and the expectation of the BD with and , and assuming that the phase shift of the phase modulator in FIG. 4 is set toby:which is identical to that of the OPC receiver [see Eq. (6)]. On the other hand, in this classical coherent detection receiver one can use the phase-conjugated idler photon at the local oscillator (LO) laser port, while the received signal photons at the signal port. The corresponding BD photocurrent operator variance is given by:085067-817582 (UA24-038) and

[0058] When M-ary QAM is used instead of PSK, one can havethat where is the signal constellation point, so that for the the BD photocurrent operator is given by: which ispoint. For the expectation of the BD photocurrent operator is now: which ispoint.

[0059] In the absence of atmospheric turbulence, the entanglement assisted channel capacity,assuming that the Gaussian modulation can be used, is determined by:wherein , where the OPC is performed on the idler photons. Therefore, in the absence of turbulence, the two schemes (i.e., conducting the OPC on signal photons on transmitter side and OPC on idler photons) perform similarly. By performing the OPC on the transmitter side, the corresponding Wigner covariance matrix changes, and the phase-sensitive cross-correlation changes as well. Therefore, those two schemes will perform differently in the presence of turbulence or for any other non-Gaussian channel. By performing the OPC on085067-817582 (UA24-038) signal photons on receiver side, when signal photons are either absorbed or scattered by the turbulent medium, the cross-correlation will be lower compared to that when the OPC is performed on idler photons that are not affected by turbulence effects at all. Thus the higher SNR in the proposed scheme will result in higher spectral efficiency.

[0060] Based on Eqs. (9) and (12), the phase shift introduced by the presence of the target(which is denoted as ) can be determined as follows:

[0061] Because theis the wavenumber, the range to the target can be determined.

[0062] FIG. 5 illustrates a non-limiting example of an entanglement assisted radar system thatis applicable to both monostatic and bistatic radar concepts. Entanglement assisted radar system 500 includes a transmitter (i.e., transmitter 502), a transmitted beam 504, an FSO channel 506, a receiver (i.e., receiver 508), and an adaptive optics (AO) subsystem (i.e., adaptive optics system 528). Transmitter 502 includes entangled source 510, modulator 514, and expanding telescope 516. Receiver 508 includes quantum memory 518 (e.g., an optical memory or optical delay line) , detector 520, and target detection processor 522 that generates detection results 524 based on the cross-correlation of the signal from detector 520 and modulation pattern 538. Adaptive optics system 528 includes beam splitter 526, AO processor 512, deformable mirror 530, and wavefront sensor 532. Entanglement assisted radar system 500 also includes compressing telescope 540 that collects light from the radar return signal, which is provided to receiver 508 (e.g., through the beam splitter BS 526) and adaptive optics system 528 as the received signal. Further, entanglement assisted radar system 500 includes optical phase- conjugation module 542 that converts an idler beam (e.g., idler photons 548) to phase- conjugated idler photons 550 and includes quantum memory 518 (e.g., a fiber optic delay line) that stores the idler to match the delay of the signal photons 544 to and from target 534.

[0063] According to certain non-limiting examples, transmitter 502 includes an entangled-photon source (e.g., entangled source 510) that generates signal photons 544 and idler photons 548. Further, transmitter 502 includes a modulator (e.g., modulator 514) that modulates signal photons 544 according to a predefined modulation scheme to generate a modulated optical085067-817582 (UA24-038) signal. Additionally, transmitter 502 includes output optics (e.g. coupling optics, such as a collimator, and expanding telescope 516) that transmit the modulated radar signal from the transmitter through free space towards a target. For example, the predefined modulation scheme can use phase shift keying (PSK) modulation and the pattern can be a digital code (modulation pattern 538) that is encoded on signal photons 544.

[0064] The radar return signal from 534 can be collected at compressing telescope 540, whichprovides the received signal to adaptive optics system 528 and receiver 508.

[0065] According to certain non-limiting examples, the received signal is detected by detector520 of receiver 508. Detector 520 can be a balanced homodyne detector that mixes the received optical signal (i.e., radar return signal photons) with phase-conjugated idler photons 550, which functions as a local oscillator to provide a mixed signal that is detected by a balanced photoreceiver to generate an electrical radio frequency (RF) signal. Further, detector 520 can include an analog-to-digital converter that converts the electrical signal to a digital signal. Additionally, receiver 508 can include one or more processors (e.g., target detection processor 522) that process the digital signal to detect the target.

[0066] According to certain non-limiting examples, the modulation scheme used to modulatethe light uses constant amplitude modulation to encode a pattern (e.g., modulation pattern 538) on the signal photons from the entanglement generation source, and the target detection processor 522 uses a cross-correlation between the pattern and the digital signal to detect the target.

[0067] According to certain non-limiting examples, adaptive optics system 528 includes adeformable mirror (e.g., deformable mirror 530) arranged in an optical path of the reflected / scattered light before the balanced detector (e.g., detector 520).

[0068] Further, adaptive optics system 528 can include the beam splitter 526, which can beimplemented as a partially reflected mirror or dielectric mirror, arranged in the optical path between compressing telescope 540 and detector 520, wherein the smaller portion of the compressed reflected light beam is passed to deformable mirror 530, while the rest to detector 520. Additionally, adaptive optics system 528 can include a wavefront sensor (e.g., wavefront sensor 532) that measures the wavefront of the reflected / scattered light using the part of the reflected / scattered light. Adaptive optics system 228 can also include a processor (e.g., target085067-817582 (UA24-038) detection processor 522) that controls a deformation of the deformable mirror to realize a desired wavefront shape for the wavefront of the reflected / scattered light.

[0069] According to certain non-limiting examples, adaptive optics system 528 increases theamount of the reflected / scattered light that is coupled into the receiver by changing a shape of a wavefront of the reflected / scattered light.

[0070] According to certain non-limiting examples, adaptive optics system 528 reduces thewavefront distortion of the received beam and improves the coupling into the fiber.

[0071] According to certain non-limiting examples, adaptive optics system 528 dynamicallyadapts to wavefront distortions of the reflected / scattered light, the wavefront distortions being caused by atmospheric turbulence between the receiver and the target.

[0072] According to certain non-limiting examples, adaptive optics system 528 dynamicallyadapts to wavefront distortions of the reflected / forward scattered light, the wavefront distortions being caused by atmospheric turbulence between the transmitter and target and then the target and the receiver.

[0073] According to certain non-limiting examples, expanding telescope 516 can launchtransmitted beam 504 from transmitter 502 through free-space FSO channel 506 towards target 534. Upon reaching target 534, a portion of transmitted beam 504 (e.g., reflected / forward scattered beam 536) is scattered back towards receiver 508. For example, the optical signal from transmitter 502 can transition to free-space propagation from an optical fiber, a photonic waveguide, free-space optics, or other optical format that is used to generate, condition, modulate, and otherwise prepare the optical signal.

[0074] According to certain non-limiting examples, the optical signal can be modulated usinga modulator to generate a binary phase shift keying (BPSK) signal that encodes a transmitted pattern / sequence (e.g., modulation pattern 538), which is known to both the receiver and the transmitter.

[0075] According to certain non-limiting examples, transmitter 502 includes an entangledsource that generates a first optical field (e.g., signal photons 544) in a first quantum state and a second optical field (e.g., idler photons 548) in a second quantum state, and a photon pair of a signal photon 544 and an idler photon 548 comprises a quantum entangled state. Receiver 508 include a balanced detector that receives the received field at a first port and receives a phase- conjugated field at a second port to generate an electrical signal. Entanglement assisted radar085067-817582 (UA24-038) system 500 includes a phase-conjugate component (e.g., optical phase-conjugation module 542) arranged in an optical path of the idler photons 548 between the entangled source and the balanced detector, the phase-conjugate component applying phase conjugation to the second optical field to generate the phase-conjugated field

[0076] According to certain non-limiting examples, the entangled source uses spontaneousparametric down conversion to generate a signal field as the first optical field and an idler field as the second optical field, and the quantum entangled state is two-mode squeezed vacuum state.

[0077] According to certain non-limiting examples, the transmitter includes a modulator thatmodulates the first optical field before the output optics to encode a modulation pattern on the first optical field, and the balanced detector uses a balanced beam splitter to combine a first- port input with a second-port input and uses a homodyne balanced detector to detect outputs from the balanced beam splitter to generate the electrical signal.

[0078] According to certain non-limiting examples, entanglement assisted radar system 500 isa remote sensing system, the output optics transmit the first optical field towards a target, the input optics receive a return signal from the target as the received field, and the system further comprises one or more processors analyze the electrical signal to detect the target based on a correlation of the modulation pattern and the electrical signal.

[0079] According to certain non-limiting examples, the balanced detector uses homodynedetection to beat the received field with the phase-conjugated field to generate the electrical signal, and the one or more processors analyze the electrical signal by applying a cross- correlation method to detect the target.

[0080] FIG. 6 illustrates an example method 600 for entanglement assisted (EA) radardetection. Although the example method 600 depicts a particular sequence of operations, the sequence may be altered without departing from the scope of the present disclosure. For example, some of the operations depicted may be performed in parallel or in a different sequence that does not materially affect the function of the method 600. In other examples, different components of an example device or system that implements the method 600 may perform functions at substantially the same time or in a specific sequence.

[0081] According to some examples, the method includes generating, by an entangled sourceof a transmitter, a first optical field (e.g., signal photons) and a second optical field (e.g., idler085067-817582 (UA24-038) photons) that are in quantum entangled state at block 602. For example, entangled source 510 illustrated in FIG.5 may generate, by an entangled source of a transmitter, a first optical field (e.g., signal photons) and a second optical field (e.g., idler photons) that are in quantum entangled state.

[0082] For example, the entangled source includes a first nonlinear crystal / waveguide that ispumped by light at a pump frequency to generate, via parametric down conversion, entangled photon pairs that respectively include a first photon at a first frequency and a second photon at a second frequency, wherein the first optical field includes the first photons of the entangled photon pairs, the second optical field includes the second photons of the entangled photon pairs, and the pump frequency equals a sum of the second frequency and the first frequency. Further, the first nonlinear crystal / waveguide and the second nonlinear crystal / waveguide can be periodically poled lithium niobate (LiNbO3) crystals / waveguides. The pump frequency can be a C-band (or near C-band, e.g., but not limited to L-band, E-band, O-band, U-band, and S- band) pump frequency.

[0083] According to some examples, the method includes using a phase-conjugate component(also referred to as a phase-conjugate module) to apply phase conjugation to the second optical field to generate a phase-conjugated field at block 604. For example, optical phase-conjugation module 542 illustrated in FIG.5 may use a phase-conjugate component to apply phase conjugation to the second optical field to generate a phase-conjugated field.

[0084] For example, the phase-conjugate component includes a second nonlinearcrystal / waveguide that is pumped by the light at the first frequency to generate the phase- conjugated field by difference frequency mixing of the light at the pump frequency and the second photons.

[0085] According to some examples, the method includes storing, in an optical memory, atleast one of the second optical field or the phase-conjugated field at block 606. For example, quantum memory 518 illustrated in FIG. 5 may store, in an optical memory, at least one of the second optical field or the phase-conjugated field.

[0086] For example, the optical memory can be a free-space or fiberoptic delay line.

[0087] According to some examples, the method includes modulating, by a modulator of thetransmitter, the first optical field to encode a modulation pattern on the first optical field at085067-817582 (UA24-038) block 608. For example, modulator 514 illustrated in FIG.5 may modulate, by a modulator of the transmitter, the first optical field to encode a modulation pattern on the first optical field.

[0088] According to some examples, the method includes transmitting the first optical field asa transmitted field to a target, which reflects or forward scatters part of the transmitted field as a radar return at block 610. For example, expanding telescope 516 illustrated in FIG.5 may transmit the first optical field as a transmitted field to a target, which reflects or forward scatters part of the transmitted field as a radar return.

[0089] According to some examples, the method includes receiving the radar return signalfrom transmitted field to provide a received field at block 612. For example, compressing telescope 540 illustrated in FIG.5 may receive the radar return signal from the transmitted field to provide a received field.

[0090] According to some examples, the method includes modifying a wavefront of thereceived field using an adaptive optics system at block 614. For example, adaptive optics system 528 illustrated in FIG.5 may modify a wavefront of the received field using an adaptive optics system.

[0091] For example, the adaptive optics system can include a deformable mirror arranged inan optical path of the received field before the receiver, a wavefront sensor that measures a wavefront of received field, a beam splitter, and an adaptive optics controller. The beam splitter can be arranged in the optical path between the deformable mirror and the receiver, the beam splitter including a partially reflecting mirror or dielectric mirror that reflects less than 20% of the received field to the wavefront sensor and passes a remainder of the received field to the input optics. The adaptive optics controller can include a processor that controls a deformation of the deformable mirror to realize a desired wavefront shape for the wavefront of the received field. Further, modifying the wavefront of the received field can include dynamically adapting to wavefront distortions of the received field, the wavefront distortions being caused by atmospheric turbulence along a path of the first optical field from the transmitter to the receiver.

[0092] According to some examples, the method includes inputting the received field at a firstport of a balanced detector and the phase-conjugated field at a second port of the balanced detector to generate an electrical signal at block 616. For example, detector 520 illustrated in085067-817582 (UA24-038) FIG. 5 may input the received field at a first port of a balanced detector and the phase- conjugated field at a second port of the balanced detector to generate an electrical signal.

[0093] According to some examples, the method includes analyzing the electrical signal todetect the target based on a correlation of the modulation pattern and the electrical signal at block 618. For example, target detection processor 522 illustrated in FIG.5 may analyze the electrical signal to detect the target based on a correlation of the modulation pattern and the electrical signal.

[0094] FIG. 7 illustrates an example implementation of the systems and methods disclosedherein. Further, this example implementation was used in a case study demonstrating the efficacy of the systems and methods disclosed herein.

[0095] The case study provides an experimental demonstration of an entanglement assisted(EA) radar operating over turbulent terrestrial FSO channels. Test bed 700 is used to demonstrate the disclosed EA quantum radar technique over turbulent FSO channels or to obtain experimental results of EA assisted radar operations, one can develop an FSO testbed. Corner cube 720 is used as the target and is placed on a roof-top, which is a distance d=750 m away from the radar. Test bed 700 is divided into several stages: entangled photon pairs generation stage (e.g., tunable laser 702, erbium-doped fiber amplifier 704, entanglement source 706, and coarse wavelength division multiplexer 708), optical transceiver (e.g., modulator 714, beam expander 716, beam compressor 722, mirrors 724, and fiber coupler 726), FSO link with the target, adaptive optics (AO) stage (e.g., deformable mirror 734, beam splitter 736, wavefront sensor 738, and adaptive optics processor 740), and the homodyne detection stage (e.g., optical phase-conjugation PPLN waveguide 710, optical delay line 712, balanced detector 728, real-time scope 730 or an analog-to-digital converter, and computer 732).

[0096] According to certain non-limiting examples, test bed 700 provides the generation ofentangled photon pairs, which can be generated using a tunable laser 702 that is tuned at 1529.75 nm. The output signal from tunable laser 702 is further amplified using a high-power EDFA (e.g., erbium-doped fiber amplifier 704), which feeds entanglement source 706. According to certain non-limiting examples, entanglement source 706 is a periodically polled lithium niobate (PPLN) waveguides-based entangled source. According to certain non-limiting examples, the PPLN waveguides-based entangled source can provide flexibility because the085067-817582 (UA24-038) PPLN waveguides-based entangled source can use a different pump wavelength to get signal photons at a desired wavelength in either C- or L-band.

[0097] In test bed 700, the output of erbium-doped fiber amplifier 704 is split into two parts.The upper part is used as the input of entanglement source 706. Coarse wavelength division multiplexer 708 is used to select 1550 nm and 1510 nm photon pairs as the signal and idler photons, respectively. That is, to separate signal and idler photons a coarse WDM (CWDM) demultiplexer can be used after entanglement source 706.

[0098] At optical phase-conjugation PPLN waveguide 710, the idler photons from coarsewavelength division multiplexer 708 are mixed with the lower part of 1529.75 nm pump from erbium-doped fiber amplifier 704 and then passed on to and optical phase-conjugation (OPC) PPLN waveguide to perform the phase-conjugation using a difference frequency generation process. Then the output of the OPC PPLN waveguide is passed through a CWDM demultiplexer, which functions as a bandpass filter to select the 1550 nm phase-conjugated idler photons as the output from optical phase-conjugation PPLN waveguide 710.

[0099] The outputs from optical phase-conjugation PPLN waveguide 710 are input to opticaldelay line 712. For example, the 1550 nm idler photons from optical phase-conjugation PPLN waveguide 710 can be passed through a single-mode fiber (SMF) that acts as an optical delay line (ODL) 712. The length of the SMF can be adjusted to match the delay incurred by the signal photons before reaching balanced detector 728. Thus, the arrival time for the reflected signal photons transmitted over the FSO link and the idler photons at the balanced detector are matched.

[0100] The signal photons from coarse wavelength division multiplexer 708 pass throughmodulator 714, beam expander 716, the transmit side of periscope 718, and the FSO channel between periscope 718 and corner cube 720 before the signal photons reach beam compressor 722, after having passed through the receive side of periscope 718. That is, the signal photons propagated towards the corner-cube retro reflector (i.e., corner cube 720), which serves as the target.

[0101] The case study was performed using FSO transmissions from the ECE 549 Lab roomin the ECE Dept. building to a second (Meinel) building rooftop, which are separated by distance “d,” which is approximately 750 m. Corner cube 720 is a retroreflector that is used a target for the proof of concept. The radar beam is pointed from the ECE Dept. building room085067-817582 (UA24-038) 549 towards the second (Meinel) building where a retroreflector (corner cube 720), on the rooftop is placed, which reflects beam back to the window of the ECE room 549.

[0102] The reflected signal photons from corner cube 720 (representing the radar return) arepassed through beam compressor 722 and the AO subsystem (e.g., mirrors 724, deformable mirror 734, and beam splitter 736, before being coupled into a multimode fiber (MMF) at fiber coupler 726.

[0103] The presence of the target is detected by the homodyne receiver composed of anoptical hybrid and a free space coupled balanced detector (e.g., balanced detector 728). The signal photons are applied on one input of the homodyne detector, while the phase-conjugated idler photons are used as the LO signal. The RF output from balanced detector 728 can be digitized using a real-time oscilloscope (e.g., real-time scope 730) and analyzed using computer 732 for the presence of the target.

[0104] To improve the performance in the presence of atmospheric turbulence effects the AOsubsystem is used, the AO subsystem includes a wavefront sensor (WFS) (e.g., wavefront sensor 738) and a deformable mirror (DM) (e.g., deformable mirror 734). Deformable mirror 734 and wavefront sensor 738 operate in a servo loop. Wavefront sensor 738 looks for wavefront distortions, and a powerful personal computer (e.g., adaptive optics processor 740) calculates the corresponding correction signals that are applied to deformable mirror 734 by using a DM controller to deforms the mirror in order to compensate for the wavefront distortions.

[0105] The AO system cost can be reduced, by using the residual 1529.75 nm pump signalfrom the SHG waveguide in entanglement source 706 as part of the radar beacon (e.g., the part of the 1529.75 nm pump sign that is not filtered can be used as a beacon signal to operate the AO subsystem). This is a benefit of selecting the pump signal wavelength to be 1529.75 nm rather than 1560 nm in order to not contaminate the quantum signals.

[0106] The AO subsystem improves performance in the presence of atmospheric turbulenceeffects. The AO subsystem includes wavefront sensor 738 and deformable mirror 734 operating in a servo loop. Wavefront sensor 738 detects wavefront distortions. Adaptive optics processor 740 calculates the corresponding correction signals for deformable mirror 734, and these correction signals are communicated to deformable mirror 734 to control the deformation of deformable mirror 734 to compensate for the wavefront distortions, which are due to085067-817582 (UA24-038) atmospheric turbulence. In the case study, system cost was reduced by using an 8% pickoff from the radar return signal as a beacon signal to operate the AO subsystem, which is enabled by using a constant amplitude modulation format.

[0107] Modulator 714 is drawn using a dashed line indicating that, according to certain non-limiting examples, modulator 714 can be omitted, in particular when the pulse laser is used as the pump laser. In other examples, modulator 714 is not omitted. For the case study, modulator 714 is not omitted because continuous wave (CW) laser is used as a pump laser.

[0108] FIG. 8A, FIG. 8B, and FIG. 8C show results from the case study, demonstrating theadvantages of an EA quantum radar relative to a comparable classical radar. In FIG.8A, the horizontal axis represents time indices for different transmissions over turbulent FSO link. The total transmit power of signal photons was set to 3.3 mW. To simplify the implementation, a phase-modulator (e.g., modulator 714) is used to encode on the signal photons a binary phase shift keying (BPSK) packet that has a length of 4000 bits, this packet is known to the receiver. Homodyne detection in balanced detector is realized by beating received signal photons and phase-conjugated idler photons. Following the homodyne detection in balanced detector, computer 732 uses a cross-correlation method to determine the presence of the packet and target.

[0109] For the classical radar results the received signal is a BPSK modulated beam at thewavelength of 1550 nm, and this received signal is mixed with a local oscillator (LO) laser signal in balanced detector, followed by using the cross-correlation method to determine the presence of the target. Given that the corner-cube retro reflector, serving as the target, is present all the time, the detection probability is quite straightforward to determine.

[0110] Corresponding histograms of received optical power are provided as well. The EAquantum radar was operated in a strong turbulence regime. Given that the distribution of the received power in a histogram plot in FIG.8B follows Rayleigh distribution the corresponding turbulence conditions were strong. In this turbulence regime, the classical radar was not operational at all (detection probability tends to zero and as such is not shown in the figure). The classical radar was functional in medium turbulence regime, which is provided as the red curve in FIG.8A, wherein the wide log-normal distribution of received power in FIG. 8C indicates medium turbulence regime. Clearly, the proposed EA quantum radar operating in085067-817582 (UA24-038) strong turbulence outperforms the classical radar operating in medium turbulence, thus providing a clear quantum advantage.

[0111] FIG. 8B illustrates the histogram of received optical power corresponding to the EAquantum radar measurement results. The EA quantum radar was operated in a strong turbulence regime, as evidenced by the received optical power distribution being a Rayleigh-like distribution. When the received power in a histogram plot follows Rayleigh distribution the corresponding turbulence conditions were strong.

[0112] FIG. 8C illustrates the histogram of received optical power corresponding to theclassical radar measurement results. The classical radar was operated in a medium turbulence regime, as evidenced by the received optical power distribution having a distribution that appears to be between Rician and log-normal distributions. The wide log-normal distribution of received power indicates a medium turbulence regime.

[0113] Based on FIG. 8A, FIG. 8B, and FIG. 8C, it can be observed that the EA quantumradar operating in strong turbulence outperforms the classical radar operating in medium turbulence, demonstrating the advantage of the EA quantum radar relative to the classical radar.

[0114] FIG. 9 shows a comparison of results for the EA quantum radar with and without usingadaptive optics (AO), when operating in the strong turbulence regime. Here, the AO was designed to operate in weak turbulence regime for astronomic applications. Nevertheless, it provides the relevant improvements in target detection probabilities in strong turbulence regime for the proposed EA quantum radar technique.

[0115] The FSO experiment in which OPC is performed on receive side is extremely difficultbecause one would need to couple the beam to the single-mode fiber (SMF), with typical core diameter 9-10 µm. In strong turbulence, because of the beam wandering introduced by turbulence, will have too frequent outages. Performing the OPC in this condition is practically impossible. In the proposed scheme, one can use the multi-mode fiber (MMF) of 1 mm in core diameter to couple the beam, which makes the system reliable even in the strong turbulence regime. This is why one can perform the comparison with classical case only.

[0116] FIG. 10 illustrates a C-band pump-based multiwavelength entangled-photon sourcesuitable to implement in photonic integrated circuits. The 1550-nm and 1570-nm bands are entangled; 1530-nm and 1590-nm bands are also entangled. The illustrated concept can generate entangled states based on telecom C-band (or near C-band) devices.085067-817582 (UA24-038)

[0117] Previous approaches to generate entangled states suitable for quantum communicationover fiber-optics links have used the expensive high-power 780 nm pump laser. The systems and methods disclosed herein can provide a more cost-effective approach for generating entangled states suitable for quantum communication over both fiber-optics and FSO links.

[0118] For high-speed EA communications, the linewidth of 780 nm pump laser should be inthe order of tens of kHz. Such high-power tunable lasers could be orders of magnitude more expensive compared to the corresponding C-band tunable lasers. FIG.10 illustrate a solution to generate entangled states that uses mature, low-cost telecom devices operating in the C-band (or near C-band), including tunable lasers, PPLN waveguides, wavelength division multiplexing (WDM) demultiplexers, and tunable optical filters. Thanks to a strong Pockels nonlinearity, several critical quantum devices have been implemented already using the same LiNbO3 platform such as heralded single-photon source, squeezed light generator, and quantum frequency / wavelength conversion module. In addition to entanglement generation with parametric down-conversion, the strong Pockels coefficient (^^33~30 pm / V) enables fast reconfiguration of quantum transceivers. Moreover, the LiNbO3 material has a very broad transparency window (from 400 nm to 5 µm), which makes it an excellent material for the generation of entangled states by employing the C-band devices. By using this concept, one can generate bright entangled photons enabling the distribution of entanglement even over terrestrial free-space optical links in the presence of strong turbulence. So far either fiber-optics links or satellite-to-ground links have been used to distribute entanglement. Moreover, the PPLN waveguides have already been used in fiber-optics communications to perform the phase-conjugation of the whole WDM comb to deal with fiber nonlinearities.

[0119] The entangled-photon source shown in FIG. 10 (e.g., entangled photon source 1000)includes pump laser 1002, second harmonic generation crystal / waveguide 1004, bandpass filter 1008, parametric down-conversion crystal / waveguide 1006, and coarse wavelength division multiplexer (CWDM) demultiplexer 1010. Entangled photon source 1000 generates entangled photons 1014. According to certain non-limiting examples, entangled photon source 1000 uses type-0 PPLN waveguide (i.e., the waveguide suppresses higher-order spatial modes) that is pumped by a continuous-wave 1560 nm laser signal (pump laser 1002). Second-harmonic generation occurs in the first PPLN waveguide (second harmonic generation crystal / waveguide 1004), which converts the 1560 nm pump signal to the secondary 780 nm pump. The properly085067-817582 (UA24-038) designed optical bandpass filter passes 780nm signal and blocks residual 1560 nm pump signal. The PDC process occurs in the second PPLN waveguide (parametric down-conversion crystal / waveguide 1006). Entangled photon source 1000 can be fabricated to ensure that higher- order spatial-mode processes are suppressed. The PPLN waveguides can interface to one or more polarization maintaining 1550 nm fibers that have FC / APC connectors, and an integrated thermistor / Peltier thermoelectric cooler to optimize the operating temperature. Given that the phase-matching bandwidth of the PPLN waveguide is very wide, one can use a commercial coarse wavelength division multiplexer (CWDM) demultiplexer to separate out four channels each with a 16-nm bandwidth centered around 1530, 1550, 1570, and 1590 nm, respectively. Due to energy conservation, the photons in the 1530-nm and 1590-nm bands are entangled. In a similar fashion, photons in the 1550-nm and 1570-nm bands also form pairs of time-energy entangled photons.

[0120] FIG. 11 illustrates coincidence count measurement results for 1530nm−1570nmentangled photon pairs in a back-to-back configuration.

[0121] To illustrate high potential of the proposed C-band pump-based multiwavelengthentangled-photon source, one can conduct the experiment according to FIG.10 and measure the coincidence counts between signal photons at 1550 nm and idler photons at 1570 nm with the help of the Nucrypt correlated photon detection system, clocked at 50 MHz, and corresponding results are summarized in FIG.11. In the same figure, one can also provide coincidence counts results when 780 nm pump laser from TOPTICA (DLC DL PRO 780 FD2 S) was used. It can be observed that the proposed C-band devices-based entanglement generation source provides orders of magnitude higher coincidence counts.

[0122] FIG. 12A and FIG. 12B show non-limiting examples of EA sensing modules andarchitectures as two configurations based on lithium niobate (LN) thin-films and reflective and transmissive Slepian fiber Bragg gratings (FBGs). The FBGs can be implemented as reflective devices, while the transmissive FBGs depend on a special design.

[0123] The Slepian-FBGs provide orthogonal impulse responses which can be used todistinguish different FBGs placed on different locations. Both reflective and transmissive configurations can be used to implement optomechanical, optical, and electro-optical (EO) quantum sensors.085067-817582 (UA24-038)

[0124] FIG. 12A shows a reflective architecture 1202 to be used for an EA sensing module.The reflective architecture 1202 uses PDC source and OPC module 300 to generate signal photons and idler photons. The idler photons are stored in quantum memory 1206 before they are received at one input of homodyne balanced detector 1204. The signal photons are directed through circulator 1210 towards a series of Slepian-FBGs (e.g., Slepian FBG sensor 1212a, …, Slepian FBG sensor 1212a, …, Slepian FBG sensor 1212a) that reflect the signal photons back to circulator 1210, which directs the reflected signal photons through tunable Slepian conjugate FBG 1208 to the other input to homodyne balanced detector 1204. Homodyne balanced detector 1204 mixes the received idler photons with the received signal photons to perform balanced homodyne detection to generate an electrical signal.

[0125] In reflective architecture 1202 shown in FIG. 12A, PDC source and OPC module 300can use a parametric down conversion (PDC) based on PPLN waveguide to generate the signal and idler photons. PDC source and OPC module 300 also includes an optical phase-conjugation (OPC) module that performs phase conjugation on the idler photons. The idler photons are stored in quantum memory 1206 (e.g., an optical delay line). According to certain non-limiting examples, PDC source and OPC module 300 can be an integrated device in which a PDC source is integrated with an OPC module on the same chip through a periodically polled thin- film LN waveguide technology with fabrication. The signal photons are then transmitted towards the reflective Slepian-FBG sensors with fixed optical impulse responses (e.g., Slepian FBG sensor 1212a, …, Slepian FBG sensor 1212a, …, Slepian FBG sensor 1212a). The sensing parameters will modify the impulse response, and as such modulate the corresponding impulse responses of the Slepian-FBG sensor. After reflection, corresponding signal photons will pass through circulator 1210 towards a tunable conjugate Slepian-FBG (e.g., tunable Slepian conjugate FBG 1208), which selects the reading from a desired FBG-sensor. At homodyne balanced detector 1204, beating between signal and idler photons is used to perform balanced homodyne detection to measure the amplitude and phase variations corresponding the respective Slepian-FBG sensors.

[0126] FIG. 12B shows a transmissive architecture 1240 to be used for an EA sensing module.In FIG.12B, the transmissive Slepian-FBGs’ based configuration includes multipartite entangled source 1242 such as one provided in FIG. 10, which directs respective signal photons through fiber Bragg gratings 1244 followed by optical sensors 1246 and conjugate fiber Bragg085067-817582 (UA24-038) gratings 1248. The idler photons at balanced detectors 1250 can be phase-conjugated idler photons that are distributed before quantum sensing occurs. To reduce the cost, EO (entanglement optical) sensors can be based on a thin-film LN phase modulator to detect the presence of high-speed electrical and electromagnetic fields.

[0127] FIG. 13 shows an example of computing system 1300. The computing system 1300 canbe AO processor 512, target detection processor 522, adaptive optics processor 740, and / or computer 732. The computing system 1300 can perform the functions of method 600. The computing system 1300 can be part of a distributed computing network in which several computers perform respective steps in method 600 and / or the functions of entanglement assisted radar system 500. The computing system 1300 can be connected to the other parts of the distributed computing network via connection 1302 or communication interface 1328. Connection 1302 can be a physical connection via a bus, or a direct connection into processor 1304, such as in a chipset architecture. Connection 1302 can also be a virtual connection, networked connection, or logical connection.

[0128] In some embodiments, computing system 1300 is a distributed system in which thefunctions described in this disclosure can be distributed within a datacenter, multiple data centers, a peer network, etc. In some embodiments, one or more of the described system components represents many such components each performing some or all of the function for which the component is described. In some embodiments, the components can be physical or virtual devices.

[0129] Example computing system 1300 includes at least one processing unit (CPU orprocessor) 1304 and connection 1302 that couples various system components including system memory 1308, such as read-only memory (ROM) 1310 and random access memory (RAM) 1312 to processor 1304. Computing system 1300 can include a cache of high-speed memory 1306 connected directly with, in close proximity to, or integrated as part of processor 1304. Processor 1304 may essentially be a completely self-contained computing system, containing multiple cores or processors, a bus, memory controller, cache, etc. A multi-core processor may be symmetric or asymmetric.

[0130] Processor 1304 can include any general-purpose processor and a hardware service orsoftware service, such as services 1320, 1322, and 1324 stored in storage device 1314,085067-817582 (UA24-038) configured to control processor 1304 as well as a special-purpose processor where software instructions are incorporated into the actual processor design.

[0131] To enable user interaction, computing system 1300 includes an input device 1330,which can represent any number of input mechanisms, such as a microphone for speech, a touch-sensitive screen for gesture or graphical input, keyboard, mouse, motion input, speech, etc. Computing system 1300 can also include output device 1326, which can be one or more of a number of output mechanisms known to those of skill in the art. In some instances, multimodal systems can enable a user to provide multiple types of input / output to communicate with computing system 1300. Computing system 1300 can include a communication interface 1328, which can generally govern and manage the user input and system output. There is no restriction on operating on any particular hardware arrangement, and therefore the basic features here may easily be substituted for improved hardware or firmware arrangements as they are developed.

[0132] Storage device 1314 can be a non-volatile memory device and can be a hard disk orother types of computer-readable media that can store data that are accessible by a computer, such as magnetic cassettes, flash memory cards, solid state memory devices, digital versatile disks, cartridges, random access memories (RAMs), read-only memory (ROM), and / or some combination of these devices.

[0133] The storage device 1314 can include software services, servers, services, etc., thatwhen the code that defines such software is executed by processor 1304, it causes the system to perform a function. In some embodiments, a hardware service that performs a particular function can include the software component stored in a computer-readable medium in connection with the necessary hardware components, such as processor 1304, connection 1302, output device 1326, etc., to carry out the function.

[0134] For clarity of explanation, in some instances, the present technology may be presentedas including individual functional blocks including functional blocks comprising devices, device components, steps or routines in a method embodied in software, or combinations of hardware and software.

[0135] Any of the steps, operations, functions, or processes described herein may beperformed or implemented by a combination of hardware and software services or services, alone or in combination with other devices. In some embodiments, a service can be software085067-817582 (UA24-038) that resides in memory of an AO processor 512, target detection processor 522, adaptive optics processor 740 and performs one or more functions of method 600 when a processor executes the software associated with the service. In some embodiments, a service is a program or a collection of programs that carry out a specific function. In some embodiments, a service can be considered a server. The memory can be a non-transitory computer-readable medium.

[0136] In some embodiments, the computer-readable storage devices, mediums, and memoriescan include a cable or wireless signal containing a bit stream and the like. However, when mentioned, non-transitory computer-readable storage media expressly exclude media such as energy, carrier signals, electromagnetic waves, and signals per se.

[0137] Methods according to the above-described examples can be implemented usingcomputer-executable instructions that are stored or otherwise available from computer-readable media. Such instructions can comprise, e.g., instructions and data that cause or otherwise configure a general-purpose computer, special-purpose computer, or special-purpose processing device to perform a certain function or group of functions. Portions of computer resources used can be accessible over a network. The executable computer instructions may be, e.g., binaries, intermediate format instructions such as assembly language, firmware, or source code. Examples of computer-readable media that may be used to store instructions, information used, and / or information created during methods according to described examples include magnetic or optical disks, solid-state memory devices, flash memory, USB devices provided with non-volatile memory, networked storage devices, and so on.

[0138] Devices implementing methods according to these disclosures can comprise hardware,firmware and / or software, and can take any of a variety of form factors. Typical examples of such form factors include servers, laptops, smartphones, small form factor personal computers, personal digital assistants, and so on. The functionality described herein also can be embodied in peripherals or add-in cards. Such functionality can also be implemented on a circuit board among different chips or different processes executing in a single device, by way of further example.

[0139] The instructions, media for conveying such instructions, computing resources forexecuting them, and other structures for supporting such computing resources are means for providing the functions described in these disclosures.085067-817582 (UA24-038)

[0140] For clarity of explanation, in some instances the present technology may be presentedas including individual functional blocks including functional blocks comprising devices, device components, steps or routines in a method embodied in software, or combinations of hardware and software.

[0141] Any of the steps, operations, functions, or processes described herein may beperformed or implemented by a combination of hardware and software services or services, alone or in combination with other devices. In some embodiments, a service can be software that resides in memory of a client device and / or one or more servers of a content management system and perform one or more functions when a processor executes the software associated with the service. In some embodiments, a service is a program, or a collection of programs that carry out a specific function. In some embodiments, a service can be considered a server. The memory can be a non-transitory computer-readable medium.

[0142] In some embodiments the computer-readable storage devices, mediums, and memoriescan include a cable or wireless signal containing a bit stream and the like. However, when mentioned, non-transitory computer-readable storage media expressly exclude media such as energy, carrier signals, electromagnetic waves, and signals per se.

[0143] Methods according to the above-described examples can be implemented usingcomputer-executable instructions that are stored or otherwise available from computer readable media. Such instructions can comprise, e.g., instructions and data which cause or otherwise configure a general-purpose computer, special purpose computer, or special purpose processing device to perform a certain function or group of functions. Portions of computer resources used can be accessible over a network. The computer executable instructions may be, e.g. binaries, intermediate format instructions such as assembly language, firmware, or source code. Examples of computer-readable media that may be used to store instructions, information used, and / or information created during methods according to described examples include magnetic or optical disks, solid state memory devices, flash memory, USB devices provided with non- volatile memory, networked storage devices, and so on.

[0144] Devices implementing methods according to these disclosures can comprise hardware,firmware and / or software, and can take any of a variety of form factors. Typical examples of such form factors include servers, laptops, smart phones, small form factor personal computers, personal digital assistants, and so on. Functionality described herein also can be embodied in085067-817582 (UA24-038) peripherals or add-in cards. Such functionality can also be implemented on a circuit board among different chips or different processes executing in a single device, by way of further example.

[0145] The instructions, media for conveying such instructions, computing resources forexecuting them, and other structures for supporting such computing resources are means for providing the functions described in these disclosures.

[0146] Although a variety of examples and other information was used to explain aspectswithin the scope of the appended claims, no limitation of the claims should be implied based on particular features or arrangements in such examples, as one of ordinary skill would be able to use these examples to derive a wide variety of implementations. Further and although some subject matter may have been described in language specific to examples of structural features and / or method steps, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to these described features or acts. For example, such functionality can be distributed differently or performed in components other than those identified herein. Rather, the described features and steps are disclosed as examples of components of systems and methods within the scope of the appended claims.

[0147] The operations of the systems disclosed herein can be performed via a computingdevice having a processor, a bus, a computer-readable memory and so forth. The term one or more processors or processor can encompass one or more of an application-specific integrated circuit (ASIC), a field programmable gate array (FPGA), or a more traditional computer processor. In many cases, radar systems as disclosed do not use standard computer processors but use ASICs or FPGAs to perform their operations.

[0148] While the present disclosure has been described with reference to variousembodiments, it should be understood that these embodiments are illustrative and that the scope of the disclosure is not limited to them. Many variations, modifications, additions, and improvements are possible. More generally, embodiments in accordance with the present disclosure have been described in the context of particular implementations. Functionality may be separated or combined in blocks differently in various embodiments of the disclosure or described with different terminology. These and other variations, modifications, additions, and improvements may fall within the scope of the disclosure as defined in the claims that follow. To illustrate, the proposed concept is directly applicable to the bistatic radars, in which085067-817582 (UA24-038) transmitters and receivers are separated. In this scenario, the forward scattered beam from the target is used instead of the reflected beam in the monostatic scenario.

[0149] Claim clauses include:

[0150] Clause 1. A system comprising: a transmitter that includes: an entangled source thatgenerates a first optical field and a second optical field in a second quantum state, and a combination of the first optical field and the second optical field comprising a quantum entangled state, and output optics that transmit the first optical field to provide a transmitted field; an optical memory that stores the second optical field; a receiver that includes: input optics that receive the transmitted field to provide a received field, and a balanced detector that receives the received field at a first port and receives a phase-conjugated field at a second port to generate an electrical signal; and a phase-conjugate component arranged in an optical path of the second optical field between the entangled source and the balanced detector, the phase- conjugate component applying phase conjugation to the second optical field to generate the phase-conjugated field.

[0151] Clause 2. The system of clause 1, wherein: the entangled source uses spontaneousparametric down conversion to generate a signal field as the first optical field and an idler field as the second optical field, and the quantum entangled state is two-mode squeezed vacuum state.

[0152] Clause 3. The system of clause 1 or clause 2, wherein: the transmitter includes amodulator that modulates the first optical field before the output optics to encode a modulation pattern on the first optical field, and the balanced detector uses a balanced beam splitter to combine a first-port input with a second-port input and uses a homodyne balanced detector to detect outputs from the balanced beam splitter to generate the electrical signal.

[0153] Clause 4. The system of clause 3, wherein the modulator is an electro-optic modulatorthat modulates the first optical field using phase shift keying modulation to encode the modulation pattern on the first optical field.

[0154] Clause 5. The system of clause 3, wherein: the system is a remote sensing system, theoutput optics transmit the first optical field towards a target, the input optics receive a return signal from the target as the received field, and the system further comprises one or more processors analyze the electrical signal to detect the target based on a correlation of the modulation pattern and the electrical signal.085067-817582 (UA24-038)

[0155] Clause 6. The system of clause 5, wherein: the balanced detector uses homodynedetection to beat the received field with the phase-conjugated field to generate the electrical signal, and the one or more processors analyze the electrical signal by applying a cross- correlation method to detect the target.

[0156] Clause 7. The system of clause 3, wherein: the system is a communication system, themodulation pattern uses a modulation scheme to encode a codeword (or modulation) on the first optical field, and the system further comprises one or more processors analyze the electrical signal to recreate the codeword (or modulation) from the electrical signal.

[0157] Clause 8. The system of any of clause 1 through clause 7, further comprising anadaptive optics system that comprises: a deformable mirror arranged in an optical path of the received field before the receiver, a wavefront sensor that measures a wavefront of the received field, a beam splitter arranged in an optical path between the deformable mirror and the receiver, the beam splitter including a partially reflecting mirror or dielectric mirror that reflects less than 20% of the received field to the wavefront sensor and passes a remainder of the received field to the input optics, and an adaptive optics controller comprising a processor that controls a deformation of the deformable mirror to realize a desired wavefront shape for the wavefront of the received field.

[0158] Clause 9. The system of clause 8, wherein the adaptive optics system dynamicallyadapts to wavefront distortions of the received field, the wavefront distortions being caused by atmospheric turbulence along a path of the first optical field from the transmitter to the receiver.

[0159] Clause 10. The system of any of clause 1 through clause 9, wherein: the entangledsource includes a nonlinear crystal / waveguide that is pumped by light at a pump frequency to generate, via parametric down conversion, entangled photon pairs that respectively include a first photon at a first frequency and a second photon at a second frequency, wherein the first optical field includes the first photons of the entangled photon pairs, the second optical field includes the second photons of the entangled photon pairs, and the pump frequency equals a sum of the second frequency and the first frequency, and the phase-conjugate component includes another nonlinear crystal / waveguide that is pumped by the light at the first frequency to generate the phase-conjugated field by difference frequency mixing of the light at the pump frequency and the second photons.085067-817582 (UA24-038)

[0160] Clause 11. The system of clause 10, wherein the nonlinear crystal / waveguide and theanother nonlinear crystal / waveguide are periodically poled lithium niobate (LiNbO3) waveguides.

[0161] Clause 12. The system of clause 10, wherein the pump frequency is a C-band (or nearC-band, e.g., but not limited to L-band, E-band, O-band, U-band, and S-band) pump frequency

[0162] Clause 13. The system of any of clause 1 through clause 12, wherein the opticalmemory is a free-space or fiberoptic delay line.

[0163] Clause 14. A method comprising: generating, by an entangled source of a transmitter, afirst optical field and a second optical field in a second quantum state, wherein a combination of the first optical field and the second optical field comprises a quantum entangled state; using a phase-conjugate component to apply phase conjugation to the second optical field to generate a phase-conjugated field; storing, in an optical memory, at least one of the second optical field or the phase-conjugated field; transmitting, from the transmitter, the first optical field to provide a transmitted field; receiving the transmitted field at a receiver to provide a received field, and inputting the received field at a first port of a balanced detector and the phase- conjugated field at a second port of the balanced detector to generate an electrical signal.

[0164] Clause 15. The method of clause 14, wherein: the entangled source uses spontaneousparametric down conversion to generate a signal field as the first optical field and an idler field as the second optical field, and the quantum entangled state is two-mode squeezed vacuum state.

[0165] Clause 16. The method of clause 14 or clause 15, further comprising: modulating, by amodulator of the transmitter, the first optical field to encode a modulation pattern on the first optical field, and generating, by the balanced detector, the electrical signal by using a balanced beam splitter to combine a first-port input with a second-port input and using a homodyne balanced detector to detect outputs from the balanced beam splitter to generate the electrical signal.

[0166] Clause 17. The method of clause 16, the modulator is an electro-optic modulator thatmodulates the first optical field using phase shift keying modulation to encode the modulation pattern on the first optical field.

[0167] Clause 18. The method of clause 16, wherein the method performs remote sensing by:transmitting the first optical field towards a target; receiving a return signal from the target as085067-817582 (UA24-038) the received field; and analyzing, by one or more processors, the electrical signal to detect the target based on a correlation of the modulation pattern and the electrical signal.

[0168] Clause 19. The method of clause 18, wherein: the balanced detector uses homodynedetection to beat the received field with the phase-conjugated field to generate the electrical signal, and the one or more processors analyze the electrical signal by applying a cross- correlation method to detect the target.

[0169] Clause 20. The method of clause 16, wherein the method performs communications by:modulating the first optical field to encode the modulation pattern, wherein the modulation pattern encodes a codeword (or modulation) on the first optical field using a modulation scheme; and analyzing, by one or more processors, the electrical signal to recreate the codeword (or modulation) from the electrical signal.

[0170] Clause 21. The method of any of clause 14 through clause 20, further comprisingmodifying a wavefront of the received field using an adaptive optics system that comprises: a deformable mirror arranged in an optical path of the received field before the receiver, a wavefront sensor that measures a wavefront of received field, a beam splitter arranged in the optical path between the deformable mirror and the receiver, the beam splitter including a partially reflecting mirror or dielectric mirror that reflects less than 20% of the received field to the wavefront sensor and passes a remainder of the received field to the input optics, and an adaptive optics controller comprising a processor that controls a deformation of the deformable mirror to realize a desired wavefront shape for the wavefront of the received field.

[0171] Clause 22. The method of clause 21, wherein modifying the wavefront of the receivedfield includes dynamically adapting to wavefront distortions of the received field, the wavefront distortions being caused by atmospheric turbulence along a path of the first optical field from the transmitter to the receiver.

[0172] Clause 23. The method of any of clause 14 through clause 22, wherein: the entangledsource includes a nonlinear crystal / waveguide that is pumped by light at a pump frequency to generate, via parametric down conversion, entangled photon pairs that respectively include a first photon at a first frequency and a second photon at a second frequency, wherein the first optical field includes the first photons of the entangled photon pairs, the second optical field includes the second photons of the entangled photon pairs, and the pump frequency equals a sum of the second frequency and the first frequency, and the phase-conjugate component085067-817582 (UA24-038) includes another nonlinear crystal / waveguide that is pumped by the light at the first frequency to generate the phase-conjugated field by difference frequency mixing of the light at the pump frequency and the second photons.

[0173] Clause 24. The method of clause 23, the nonlinear crystal / waveguide and the anothernonlinear crystal / waveguide are periodically poled lithium niobate (LiNbO3) waveguides.

[0174] Clause 25. The method of clause 23, wherein the pump frequency is a C-band (or nearC-band, e.g., but not limited to L-band, E-band, O-band, U-band, and S-band) pump frequency.

[0175] Clause 26. The method of any of clause 14 through clause 25, wherein the opticalmemory is a free-space or fiberoptic delay line.

[0176] Clause 27. A system comprising: an entangled photon pair generation engine thatgenerates an entangled photon pair; a periodically poled lithium niobate waveguide that receives a pump photon and generates, based on the pump photon, a signal photon and an idler photon; an optical phase-conjugation module configured to receive the idler photon; a quantum memory; a homodyne balanced detector; one or more processors; and a computer-readable storage medium storing instructions which, when executed by the one or more processors, cause the one or more processors to perform operations comprising: generating, by the optical phase-conjugation module and based on the idler photon, a phase-conjugated idler photon; transmitting the signal photon to a target to obtain a reflected probe signal photon; storing the phase-conjugated idler photon in the quantum memory; receiving, at the homodyne balanced detector, the reflected probe signal photon and the phase-conjugated idler photon; and detecting, at the homodyne balanced detector, one or more of an amplitude variation and a phase variation.

[0177] Clause 28. The system of clause 27, wherein the entangled photon pair generationengine comprises a C-band (or near C-band, e.g., but not limited to L-band, E-band, O-band, U- band, and S-band) pump laser, a PPLN waveguide performing as a second harmonic generation process to get a secondary pump, a bandpass filter to filter out residual C-band (or near C- band) pump, the PPLN waveguide performing a parametric down-conversion process and thus generating the entangled photon pair that get separated by a compact coarse wavelength division multiplexing (WDM) demultiplexer.085067-817582 (UA24-038)

[0178] Clause 29. The system of clause 27 or clause 28, wherein the optical phase-conjugationmodule comprises one or more of a tunable laser, a periodically polled lithium niobate waveguide performing a phase conjugation of the input idler photon that gets combined with the pump signal, a tunable filter to filter out residual pump, and a wavelength division multiplexing (WDM) demultiplexer whose corresponding output contains the phase-conjugated idler photon.

[0179] Clause 30. The system of any of clause 27 through clause 29, wherein the opticalphase-conjugation module comprises an optical phase conjugation periodically polled lithium niobate waveguide that generates the phase-conjugated idler photon.

[0180] Clause 31. The system of any of clause 27 through clause 30, wherein systemcomprises one or more reflective Slepian-fiber Bragg grating (FGB) sensor(s) with a fixed optical impulse response.

[0181] Clause 32. The system of clause 31, further comprising: a circulator; and a tunableconjugate Slepian-fiber Bragg grating (FGB), wherein the circulator routes the reflected probe signal photon to the tunable conjugate Slepian-FGB which selects a reading from a desired FBG sensor of one or more reflective Slepian-FGB sensor(s) to yield the reflected probe signal photon.

[0182] Clause 33. The system of any of clause 27 through clause 33, wherein detecting, at thehomodyne balanced detector, one or more of an amplitude variation and a phase variation further comprises beating the reflected signal probe photon and the phase-conjugated idler photon to determine a presence of a packet and the target.

[0183] Clause 34. The system of clause 33, wherein the phase-conjugated idler photonperforms a role of a local oscillator laser reference in the system.

[0184] Clause 35. The system of any of clause 27 through clause 34, wherein the quantummemory comprises a tunable optical delay line and wherein the one or more processors comprise a computer processor, an application specific integrated circuit or a field programmable gate array.

[0185] Clause 36. The system of any of clause 27 through clause 35, wherein transmitting thesignal photon to the target to generate the reflected probe signal photon occurs using an expanding telescope and the reflected probe signal photon is collected by a compressing telescope.085067-817582 (UA24-038)

[0186] Clause 37. The system of any of clause 27 through clause 36, wherein the signalphoton and the idler photon are quantum entangled particles.

[0187] Clause 38. A method comprising: generating, by an optical phase-conjugation moduleand based on an idler photon, a phase-conjugated idler photon, the idler photon generated by an entangled photon pair generation engine that generates an entangled photon pair comprising a signal photon and the idler photon; transmitting the signal photon to a target to obtain a reflected probe signal photon; storing the phase-conjugated idler photon in a quantum memory; receiving, at a homodyne balanced detector, the reflected probe signal photon and the phase- conjugated idler photon; and detecting, at the homodyne balanced detector, one or more of an amplitude variation and a phase variation.

[0188] Clause 39. An entangled assisted receiver comprising: a beam splitter; a homodynebalanced detector; one or more processors; and a computer-readable storage medium storing instructions which, when executed by the one or more processors, cause the one or more processors to perform operations comprising: receiving, at the beam splitter, a phase- conjugated idler photon; receiving, at the beam splitter, a signal photon; generating, by the beam splitter a first signal and a second phase-conjugated signal based on the idler photon and the signal photon; and detecting, at the homodyne balanced detector, one or more of an amplitude variation and a phase variation based on the first signal and the second phase- conjugated signal.

[0189] Clause 40. The entangled assisted receiver of clause 39, wherein the one or moreprocessors comprise a computer processor, an application specific integrated circuit or a field programmable gate array

[0190] Clause 41. An entangled assisted sensor comprising: a plurality of optical sensors; aplurality of transmissive Slepian-FBGs; a plurality of balanced detectors; one or more processors; and a computer-readable storage medium storing instructions which, when executed by the one or more processors, cause the one or more processors to perform operations comprising: receiving, at the plurality of optical sensors, a plurality of signal photons to generate a plurality of sensor outputs; transmitting, via the plurality of transmissive Slepian- fiber Bragg gratings (FBGs), the plurality of sensor outputs to the plurality of balanced detectors; receiving, at the plurality of balanced detectors, a plurality of idler photons; and085067-817582 (UA24-038) detecting, at the plurality of balanced detect, one or more of an amplitude variation and a phase variation based on the plurality of idler photons and the plurality of sensor outputs.

[0191] Clause 42. The entangled assisted sensor of clause 41, wherein the one or moreprocessors comprise a computer processor, an application specific integrated circuit or a field programmable gate array.

[0192] Clause 43. An entanglement assisted bistatic radar comprising: transmissioncomponents; and receiver components, wherein the transmission components and the receiver components are separated, and wherein a probe signal comprises a forward scattered signal photons from a target.

Claims

085067-817582 (UA24-038) CLAIMS What is claimed is:

1. A system comprising: a transmitter that includes: an entangled source that generates a first optical field and a second optical field in a second quantum state, and a combination of the first optical field and the second optical field comprising a quantum entangled state, and output optics that transmit the first optical field to provide a transmitted field; an optical memory that stores the second optical field; a receiver that includes: input optics that receive the transmitted field to provide a received field, and a balanced detector that receives the received field at a first port and receives a phase-conjugated field at a second port to generate an electrical signal; and a phase-conjugate component arranged in an optical path of the second optical field between the entangled source and the balanced detector, the phase-conjugate component applying phase conjugation to the second optical field to generate the phase-conjugated field.

2. The system of claim 1, wherein: the entangled source uses spontaneous parametric down conversion to generate a signal field as the first optical field and an idler field as the second optical field, and the quantum entangled state is two-mode squeezed vacuum state.

3. The system of claim 1, wherein: the transmitter includes a modulator that modulates the first optical field before the output optics to encode a modulation pattern on the first optical field, and the balanced detector uses a balanced beam splitter to combine a first-port input with a second-port input and uses a homodyne balanced detector to detect outputs from the balanced beam splitter to generate the electrical signal.

4. The system of claim 3, wherein the modulator is an electro-optic modulator that modulates the first optical field using phase shift keying modulation to encode the modulation pattern on the first optical field.085067-817582 (UA24-038) 5. The system of claim 3, wherein: the system is a remote sensing system, the output optics transmit the first optical field towards a target, the input optics receive a return signal from the target as the received field, and the system further comprises one or more processors analyze the electrical signal to detect the target based on a correlation of the modulation pattern and the electrical signal.

6. The system of claim 5, wherein: the balanced detector uses homodyne detection to beat the received field with the phase- conjugated field to generate the electrical signal, and the one or more processors analyze the electrical signal by applying a cross-correlation method to detect the target.

7. The system of claim 1, further comprising an adaptive optics system that comprises: a deformable mirror arranged in an optical path of the received field before the receiver, a wavefront sensor that measures a wavefront of the received field, a beam splitter arranged in an optical path between the deformable mirror and the receiver, the beam splitter including a partially reflecting mirror or dielectric mirror that reflects less than 20% of the received field to the wavefront sensor and passes a remainder of the received field to the input optics, and an adaptive optics controller comprising a processor that controls a deformation of the deformable mirror to realize a desired wavefront shape for the wavefront of the received field.

8. The system of claim 7, wherein the adaptive optics system dynamically adapts to wavefront distortions of the received field, the wavefront distortions being caused by atmospheric turbulence along a path of the first optical field from the transmitter to the receiver.

9. The system of claim 1, wherein: the entangled source includes a nonlinear crystal / waveguide that is pumped by light at a pump frequency to generate, via parametric down conversion, entangled photon pairs that respectively include a first photon at a first frequency and a second photon at a second frequency, wherein the first optical field includes the first photons of the entangled photon085067-817582 (UA24-038) pairs, the second optical field includes the second photons of the entangled photon pairs, and the pump frequency equals a sum of the second frequency and the first frequency, and the phase-conjugate component includes another nonlinear crystal / waveguide that is pumped by the light at the first frequency to generate the phase-conjugated field by difference frequency mixing of the light at the pump frequency and the second photons.

10. The system of claim 9, wherein the nonlinear crystal / waveguide and the another nonlinear crystal / waveguide are periodically poled lithium niobate (LiNbO3) waveguides.

11. The system of claim 9, wherein: the pump frequency is a C-band pump frequency, an L-band pump frequency, an E- band pump frequency, an O-band pump frequency, a U-band pump frequency, or an S-band pump frequency, and the optical memory is a free-space or fiberoptic delay line.

12. A method comprising: generating, by an entangled source of a transmitter, a first optical field and a second optical field in a second quantum state, wherein a combination of the first optical field and the second optical field comprises a quantum entangled state; using a phase-conjugate component to apply phase conjugation to the second optical field to generate a phase-conjugated field; storing, in an optical memory, at least one of the second optical field or the phase- conjugated field; transmitting, from the transmitter, the first optical field to provide a transmitted field; receiving the transmitted field at a receiver to provide a received field, and inputting the received field at a first port of a balanced detector and the phase- conjugated field at a second port of the balanced detector to generate an electrical signal.

13. The method of claim 12, wherein: the entangled source uses spontaneous parametric down conversion to generate a signal field as the first optical field and an idler field as the second optical field, and the quantum entangled state is two-mode squeezed vacuum state.085067-817582 (UA24-038) 14. The method of claim 12, further comprising: modulating, by a modulator of the transmitter, the first optical field to encode a modulation pattern on the first optical field, and generating, by the balanced detector, the electrical signal by using a balanced beam splitter to combine a first-port input with a second-port input and using a homodyne balanced detector to detect outputs from the balanced beam splitter to generate the electrical signal.

15. The method of claim 14, the modulator is an electro-optic modulator that modulates the first optical field using phase shift keying modulation to encode the modulation pattern on the first optical field.

16. The method of claim 14, wherein the method performs remote sensing by: transmitting the first optical field towards a target; receiving a return signal from the target as the received field; and analyzing, by one or more processors, the electrical signal to detect the target based on a correlation of the modulation pattern and the electrical signal.

17. The method of claim 16, wherein: the balanced detector uses homodyne detection to beat the received field with the phase- conjugated field to generate the electrical signal, and the one or more processors analyze the electrical signal by applying a cross-correlation method to detect the target.

18. The method of claim 12, further comprising modifying a wavefront of the received field using an adaptive optics system that comprises: a deformable mirror arranged in an optical path of the received field before the receiver, a wavefront sensor that measures a wavefront of received field, a beam splitter arranged in the optical path between the deformable mirror and the receiver, the beam splitter including a partially reflecting mirror or dielectric mirror that reflects less than 20% of the received field to the wavefront sensor and passes a remainder of the received field to the input optics, and085067-817582 (UA24-038) an adaptive optics controller comprising a processor that controls a deformation of the deformable mirror to realize a desired wavefront shape for the wavefront of the received field.

19. The method of claim 12, wherein: the entangled source includes a nonlinear crystal / waveguide that is pumped by light at a pump frequency to generate, via parametric down conversion, entangled photon pairs that respectively include a first photon at a first frequency and a second photon at a second frequency, wherein the first optical field includes the first photons of the entangled photon pairs, the second optical field includes the second photons of the entangled photon pairs, and the pump frequency equals a sum of the second frequency and the first frequency, and the phase-conjugate component includes another nonlinear crystal / waveguide that is pumped by the light at the first frequency to generate the phase-conjugated field by difference frequency mixing of the light at the pump frequency and the second photons.

20. The method of claim 19, the nonlinear crystal / waveguide and the another nonlinear crystal / waveguide are periodically poled lithium niobate (LiNbO3) waveguides.

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