Method and apparatus for quantum measurement via mode matched photon conversion

Abstract

The present disclosure relates to a generally-applicable measurement technique based on coherent quantum enhancement effects and provides embodiments with nonlinear optics. The technique utilizes parametric nonlinear processes where the information-carrying electromagnetic quanta in a number of electromagnetic modes are converted phase coherently to signature quanta in a single mode or a few modes. The phase coherence means that while the quanta before conversion may have unequal or uncertain phase values across the modes, the signature quanta converted from those different modes have the (near) uniform phase. This can lead to significant increase in the signal to noise ratio in detecting weak signal buried in strong background noise. Applications can be found in remote sensing, ranging, biological imaging, field imaging, target detection and identification, covert communications, and other fields that can benefit from improved signal to noise ratios by using the phase coherent effect.

1 . A method for discriminatively detecting electromagnetic waves, comprising the steps of:
 generating a signal beam and an idler beam in a plurality of paired modes;   transmitting the signal beam;   receiving at least a portion of the transmitted signal beam;   temporally aligning and combining the idler beam, or a copy thereof, with the at least a portion of the transmitted signal beam to form combined signal and idler beams;   generating signature photons from the combined signal and idler beams, wherein the signature photons are not quantum-entangled; and   filtering and detecting the signature photons in at least one of the plurality of paired modes.   
     
     
         2 . The method of  claim 1 , further comprising the step of storing the idler beam in an optical delay line or in a memory device. 
     
     
         3 . The method of  claim 1 , wherein the at least a portion of the transmitted signal beam is reflected from a target object. 
     
     
         4 . The method of  claim 3 , further comprising the step of scanning the angle at which the signal beam is transmitted and the time delay of the idler beam from the signal beam to remotely obtain three-dimensional information regarding the object. 
     
     
         5 . The method of  claim 1 , wherein said step of generating a signal beam and an idler beam is performed using a parametric downconversion process to generate the signal beam; and wherein said step of generating signature photons includes step of performing a phase coherent nonlinear process by subjecting the combined signal and idler beams to a parametric upconversion process, which corresponds to the time reversal of the parametric downconversion process. 
     
     
         6 . The method of  claim 1 , wherein said step of generating a signal beam and an idler beam is performed using a difference-frequency generation process by using a seedling beam; and wherein said step of generating signature photons includes the step of subjecting the combined signal and idler beams to a sum-frequency generation process, which is the time reversal of the difference-frequency generation process. 
     
     
         7 . The method of  claim 6 , wherein said step of generating a signal beam is performed using a single-mode pump and a seedling idler beam to generate the signal beam through the difference-frequency generation process. 
     
     
         8 . The method of  claim 1 , wherein said step of generating a signal beam and an idler beam is performed using a single-mode pump. 
     
     
         9 . The method of  claim 8 , wherein said filtering and detecting step includes the step of filtering the signature photons in order to keep only those in a mode that is substantially identical with that of the single-mode pump. 
     
     
         10 . The method of  claim 1 , further comprising the step of optionally compensating for mode distortion of the signal beam. 
     
     
         11 . The method of  claim 1 , further comprising the step of optionally amplifying the idler beam prior to the performance of said aligning and combining step. 
     
     
         12 . The method of  claim 1 , further comprising the step of including a noise beam in the signal beam prior to its transmission for conducting a covert communication. 
     
     
         13 . Apparatus for discriminatively detecting electromagnetic waves, comprising:
 a generator for generating a signal beam and an idler beam in a plurality of paired modes,   a transmitter for transmitting the signal beam;   a receiver for receiving at least a portion of the transmitted signal beam;   an aligning device for temporally aligning and combining the idler beam, or a copy thereof, with the at least a portion of the transmitted signal beam so as to generate signature photons from the combined signal and idler beams, wherein the signature photons are not quantum-entangled; and   a detector, including a filter, for detecting the signature photons in at least one of the plurality of paired modes.   
     
     
         14 . The apparatus of  claim 13 , further comprising a storage device for storing the idler beam. 
     
     
         15 . The apparatus of  claim 14 , wherein said storage device includes an optical delay line or a memory device. 
     
     
         16 . The apparatus of  claim 13 , further comprising at least one scanner for scanning the angle at which the signal beam is transmitted and the time delay of the idler beam from the signal beam to remotely obtain three-dimensional information relating to an object from which the signal beam is reflected and received by said receiver. 
     
     
         17 . The apparatus of  claim 13 , wherein said generator includes a parametric downconverter to generate the signal beam; and wherein said aligning device includes a parametric upconverter, which corresponds to the time reversal of said parametric downconverter, to generate the signature photons. 
     
     
         18 . The apparatus of  claim 13 , wherein said generator includes a difference-frequency generator to generate the signal beam; and wherein said aligning device includes a sum-frequency generator, which is the time reversal of the difference-frequency generator, to generate the signature photons. 
     
     
         19 . The apparatus of  claim 13 , wherein said generator includes a single-mode pump to generate the signal beam. 
     
     
         20 . A covert communication method, comprising the steps of:
 sharing identical secret keys between first and second communication nodes;   at the first node, creating a broadband idler beam based on at least one of the secret keys and combining the idler beam with a single-mode pump to generate a signal beam, the signal beam having an intensity that is lower than the surrounding ambient light;   encoding information in the signal beam by modulating its electromagnetic wave properties;   transmitting the modulated signal beam to the second node;   creating a copy of the idler beam at the second node based on at least one of the secret keys and using the copy of the idler beam to create signature photons from the signal beam received from the first node through a process corresponding to the time reversal of the signal beam generation process at the second node; and   filtering and detecting the signature photons in a single mode resembling the pump.