Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B13/00—Transmission systems characterised by the medium used for transmission, not provided for in groups H04B3/00 - H04B11/00

Definitions

• This invention relates to quantum non-locality modulated signalling methods It has been demonstrated, by Aspect and others, that under some circumstances, certain atomic species and non-linear downconversion crystals can be induced to emit pairs of photons that have correlated polarizations, depending on the 0 nature of the source, the correlated linear polarizations of the photon pairs are either always at 90 degrees to each other or always parallel to each other
• the photons can be provided in separate streams, with either one of each pair in each stream or with each photon having an equal probability of being found in either stream It has further been strongly demonstrated that, under certain conditions, these photons are not 5 emitted with any predetermined directions of linear polarization, but that the polarization states of the photons is only fixed upon measurement of the polarization of one of the photons.
• the apparatus is considered to include the system at the sending end, the system at the receiving end, and the correlated stream of photons which connect the two.
• a change in the apparatus at the sending end immediately affects the observations at the receiving end since the two ends are connected by single quantum objects with ends in both locations.
• an object of the invention to provide a means for sending information by control of non-local correlation effects in correlated pairs of quantum objects.
• the subject invention is based on two quantum physics effects: the non-local correlation of quantum states of paired quantum objects and the interaction of individual quanta with a certain sequential arrangements of spin selection devices.
• Quantum mechanics is a very successful set of rules and mathematical operators which can be used to predict the statistical behavior of a large number of quantum objects such as bosons, fermions and atoms and including, in particular, photons, the quantum units of light. Quantum mechanics does not explain why these rules work, nor why they exist in the first place. The meaning of the rules and their underlying philosophy is open to wide interpretation. The most widely accepted interpretation of quantum mechanics is called the Copenhagen Interpretation.
• the second effect employed in this invention involves the specific nature of the 5 interaction of quantum objects with spin selection devices.
• the interaction of light with polarizers is usually explained in terms of electromagnetic wave theory, in which a polarizer selectively absorbs (or reflects) the vector component of the electric field which is perpendicular to its polarization axis. This view is satisfactory when dealing with huge numbers of photons, but individual o photons show a very different view.
• the energy of a photon is directly linked to the color of the photon.
• a linear polarizer When randomly polarized light impinges upon a linear polarizer, approximately 50 percent of the light is passed, and 50 percent is absorbed or reflected, depending on the type of polarizer. (For simplicity, the following explanation will be limited to absorption polarizers). If each photon gave up half its energy by losing its electric field component that was perpendicular to the polarization axis, then the color of that 5 photon would change dramatically. No color change is noted, however, when this experiment is performed, so individual photons do not interact with polarizers in that manner. One polarization direction causes the photon to be absorbed by the polarizer, the other direction causes it to pass through it. Half the photons choose one orientation, half the other, so the net result looks the same as the electromagnetic l o theory.
• the first polarizer has a 25 horizontal polarization axis and the second a vertical polarization axis, and that the polarizers are perfectly efficient.
• the polarization state of the photon is indeterminate. (Correlated photons emitted by certain non-linear parametric down-conversion crystals possess a "latent" polarization state, but the polarization correlation between the two photons can still be
• the photon Upon encountering the first polarizer, the photon must choose either a vertical polarization or a horizontal polarization. The photon has an equal probability of choosing horizontal or vertical. If a vertical polarization is chosen, the photon will be absorbed; its polarization has now been observed. If it chooses a horizontal polarization, it will be passed by the polarizer. It is important to note that a photon which passes through a polarizer has not yet been observed, its energy has not yet been delivered to an electron, so its polarization state is still subject to change. I refer to a photon in this state as having a "latent" polarization. This does not mean that it can take any arbitrary polarization without external influence, rather it means that external influences can alter the final observed polarization.
• the third polarizer enters the experiment.
• the first polarizer encountered by a photon is usually called the polarizer, and the second is called the analyzer.
• the third polarizer is placed in between the polarizer and the analyzer, and it will be called the gate.
• the gate is oriented with its polarization axis parallel to the polarizer. It is clear that this orientation of the gate will have no effect on the passage of photons through the analyzer; the photons which pass through the polarizer will also pass the gate and be stopped by the analyzer. If the gate is oriented parallel to the analyzer, it will also have no effect on the passage of photons through the analyzer. The gate then acts like the analyzer and the photons which pass the polarizer are stopped by the gate, never even getting to the analyzer.
• a photon passing through the polarizer has a "latent” horizontal polarization (latent because it has not been observed to have this polarization).
• This "horizontally polarized” photon has a 50/50 chance of passing through the gate or being absorbed by it. When it encounters the gate, it must choose a new polarization, either parallel to the polarization axis of the gate or perpendicular to it, and be passed or absorbed, respectively.
• the photon passes the gate, it now has a "latent polarization" of 45 degrees, and instead of having a zero probability of passing the analyzer, it has a 50 percent chance Upon encountering the analyzer, the photon chooses either to be absorbed as a horizontally polarized photon, or to be passed as a vertically polarized photon Thus, 5 the original "horizontally polarized" photon is caused to become a vertically polarized photon by imposing an intermediate quantum decision upon it.
• the above objects of the present invention are accomplished by providing a method and apparatus for controlling the quantum state 0 probability distribution of one quantum object of a pair of correlated quantum objects, which method includes the steps of providing a pair of correlated quantum objects, each of said objects having a uniform quantum state probability distribution, providing a means for controlling the quantum state probability distribution of the one quantum object by using said controlling means to choose the probability distribution of the 5 observable quantum states of the other quantum object of the pair of correlated quantum objects, using said controlling means to choose the probability distribution of the quantum states of the other quantum particle, choosing whether to observe the quantum state of the other quantum object, and subsequently observing the quantum state of the one quantum object of said pair of correlated quantum objects to determine 0 if said prepared quantum state probability distribution of said one quantum object has been altered by an observation of the quantum state of the other quantum object
• information may be selectively transmitted on observation of the quantum state of the one quantum object by selectively controlling the quantum state probability distribution of the other quantum object of the pair of correlated quantum objects and thereby selective
• the method of the invention is suitable for a variety of quantum objects including bosons, fermions, and atoms, including, in particular, photons.
• the pair of correlated quantum objects may be provided as a part of a pair of streams of correlated quantum objects which may be provided by any one of a number of means including, but not limited to, a two-quantum object absorption/two-quantum emission process, o such as spin conserving two photon emission processes including, for example, atomic cascade and spontaneous emission from atomic deuterium or atomic calcium, and optical parametric down-conversion processes, including both Type I and Type II spin correlation processes.
• the source of the pair of correlated quantum objects provides a pair 5 having a randomized quantum state probability distribution.
• the quantum state probability distribution can be randomized by various means, such as by rotating the plane of polarization, or spin direction, of one stream of quantum objects and combining it with the other, unrotated stream of 0 quantum objects. Ou and Mandel 1, supra.
• the means for controlling the quantum state probability distribution of the one quantum object by using the means to choose the probability distribution of the observable quantum states of the other quantum objects consist of quantum spin selection or quantum spin altering devices such as polarizing beam splitters, Nichols 5 prisms, wave plates, Pockels cells, dichroic polarizing plastic sheet material and Stern-
• the pair of correlated quantum objects is provided as a part of separated streams of correlated quantum objects.
• correlated photons this may be accomplished by use of a device selected from the group consisting of lenses, prisms, mirrors, polarizing beam splitters and combinations o thereof in conjunction with the source for providing such correlated photons in order to provide an equal probability of first detecting either photon of a pair in either stream.
• other correlated quantum objects other than photons this may be accomplished by use of devices which are the functional equivalent of the optical devices, such as the use of a uniform magnetic field to act as a 'prism' for charged correlated quantum objects
• the step of choosing whether to alter and observe the probability distribution 5 of the quantum states of the other quantum object may selectively include either observing or not observing the quantum state of the other quantum object, depending upon whether the user of the method desires to transmit information by modulating the quantum state probability distribution of the one quantum object, or not
• by observing the quantum state of the other quantum object by means of a spin 0 selection device it is possible to select whether to alter or not to alter the probability distribution of the one quantum object depending upon the choice of spin selection device
• Fig 1 is a schematic illustration of one embodiment of my present invention
• Fig 2 is a schematic illustration of the invention of Fig 1 modified to show how the signalling can be switched
• FIG. 3 is a schematic illustration of an alternative embodiment of my present o invention.
• Fig 4 is a schematic illustration of the invention of Fig 3 modified to show how signalling can be switched
• Fig 5 is a schematic illustration of a further alternative embodiment of my invention employing a different source of photons
• 5 Fig 6 is a schematic illustration of the invention of Fig 5 modified to show how signaling can be switched
• FIG. 1 and 2 illustrate the operation of this invention by tracing the polarization states of photons emitted from a source, 10, of Type II correlated photon pairs through two different optical paths
• the paths are labeled 'other' and 'one' They are drawn as though they are parallel to each other in order to make clear the temporal relationship of the processes acting on the photons In practice these paths are more likely to extend in opposite directions from the source, 10
• Each of the zones represents a co- temporal period for the photons in both paths, the beginning and ending positions of the zones represent equivalent optical path distances for their respective photons from the source, 10
• 'other' photons will arrive at the beginning of zone 2 in the 'other' path at the same time as 'one' photons will arrive at the beginning of zone 2 in the 'one' path, and both photons of the correlated pair will have travelled the same optical path distance from the source, 10
• the zones are encountered sequentially by the photons, so the
• a source, 10, of frequency degenerate Type II correlated photon pairs provides photons into the two paths, 'other' and 'one' These photons are preferably produced by a Type II optical degenerate parametric down- conversion process, arranged such that the photons consist of an equal number of 5 correlated pair signal and idler photons which all have an equal probability of being found in either path, with one preferred caveat; if a particular photon is observed in one path then its pair photon can only be subsequently observed in the other path This caveat can be relaxed at the expense of the signal to noise ratio
• a source of this type will provide the signal and idler photons in orthogonal polarization states which 0 are related to the polarization state of the pump beam of the source For convenience, the signal photons are assumed to be vertically polarized and the idler photons are assumed to be horizontally polarized.
• Half of the light entering the 'other' path consists of vertically polarized signal photons and half consists of horizontally polarized idler photons, as shown at the top of zone 1 of the 'other' path.
• These signal 5 and idler photons are not paired with each other, but are paired with idler and signal photons, respectively, entering the 'one' path.
• the signal photons in the 'other' path are labeled SI and the idlers 12
• the signal photons in the 'one' path are labeled S2 and the idlers II .
• S I signal photons are paired with II idler photons and S2 signal photons are paired with 12 idler photons, but only upon observation of one of o the photons of a pair Until that time all signal photons and all idler photons have an equal probability of being detected in either path.
• the horizontal-vertical (H-N) polarization state of a photon and the +/- 45 degree polarization state of the same photon are complimentary quantum states subject to the Heisenberg Uncertainty principle. If complete information exists about one of 5 these states, then no information exists about its complimentary state Since the H-V state of the photons emitted from the source, 10, is completely known, the +/- 45 degree state of these photons is completely indeterminate, as shown at the bottom of zone 1 Since the signal and idler photons are degenerate in frequency, indistinguishable in +/- 45 degree polarization state, and indistinguishable in o propagation direction and in the probability of being detected in either path, the signal and idler photons are completely indistinquishable from each other I refer to this as maintaining the anonymity of the photons, and it is a requirement for maintaining observable non-local quantum correlation effects The correlated photons leaving zone 1 enter zone 2 in this uniform, anonymous state
• This invention enables signaling by discarding photons which make 'bad' polarization state choices and retaining photons which make 'good' polarization state choices
• the first of these 'purifying' steps is made in zone 2 by the +/- 45 degree polarizing beam splitter, 12, in the 'other' path
• the 'other' photons which enter polarizer 12 have an equal probability of leaving to the left with a +45 degree polarization and being detected by detector Dl, or passing straight through with a 'latent' polarization of -45 degrees This is a 'latent' polarization because the photon has not yet been observed to be in this state, and its final observed polarization state may be altered by subsequent passage through additional polarizing optics
• zone 3 the 'one' photons enter polarizing beam splitter 14, which deflects all of the single photons and half of the remaining paired photons into detector D2
• the detection of the single photons by D2 does not have any effect on the photons in the 'other' path, since the 'other' photons which were paired with the single 'one' photons were previously detected by detector Dl in zone 2
• the paired 'one' photons which are detected by D2 are observed to be in the -45 degree state, so their pairs in the 'other' path correlate to a +45 degree state, becoming single photons This is indicated by the correlation symbol labeled B.
• the 'one' photons which pass through polarizer 14 attain a latent +45 degree polarization state.
• the 'other' photons now consist of an equal mixture of single photons in the +45 degree polarization state and paired photons with a latent -45 degree polarization.
• these 'other' photons encounter +/-45 degree polarizing beam splitter 16, where the now single photons are deflected to detector D3 and the paired photons pass through, retaining their latent -45 degree polarization state.
• These remaining 'other' photons are the pairs to the remaining 'one' photons.
• the paired 'one' photons arriving in zone 5 enter horizontal-vertical (H-V) polarizer 18 and are separated with equal probabilities into rightward deflected horizontal (H) photons and downward passing vertical (V) photons.
• H-V horizontal-vertical
• the 'other' photons arriving in zone 5 enter H-V polarizer 20 and are equally divided into leftward deflected H photons and downward passing V photons in a similar manner, the H photons being reflected from mirror 22 for the same reason as the 'one' photons were reflected from mirror 23.
• Both the 'one' and the 'other' photons leave zone 5 in determinate H-V states and indeterminite +/-45 degree states.
• the H-V 'other' photons arriving in zone 6 enter polarizing beam splitters 26 and 24, respectively, and are detected in definite +/-45 degree polarization states by detectors D4a, D4b, D5a and D5b.
• Detectors D4a and D4b observe the 'other' photons which attain a +45 degree polarization state and the detectors D5a and D5b observe the 'other' photons which attain a -45 degree polarization state.
• the observation of the 'other' photons constitute correlation events which set the +/-45 degree polarization states of their pairs in the 'one' path. This is indicated by the correlation symbol labeled C.
• the single 'one' photons leaving zone 6 enter polarizers 28 and 30 in zone 7 and are observed in definite +/-45 degree polarization states by detectors D6a, D6b, D7a and D7b.
• Detectors D6a and D6b observe the 'one' photons having a +45 degree polarization state and detectors D7a and D7b observe the 'one' photons having a -45 degree polarization state.
• the probability distribution of the photons detected in zones 6 & 7, represented as a proportion of the total photons provided by source 10 into each of the 'one' and the 'other' paths which are observed to be in the +45 degree state, and the proportion in the -45 degree state.
• the probability distribution of the 'other' photons is (0.125, 0.125).
• the probability distribution of the 'one' photons also (0.125, 0.125). This will be the observed result with the H-V polarizer 20 in place.
• These 'one' probability distributions may be considered to be the first state of a binary state signalling method.
• the second state is illustrated in Figure 2.
• FIG. 2 The optical arrangement of Figure 2 is identical to that of Figure 1 , with one exception; H-V polarizer 20 has been removed from the 'other' path.
• the optical processes and polarization states of zones 1, 2, 3 and 4 of Figure 2 are the same as shown in the same zones of Figure 1.
• 'Other' photons entering zone 5 pass through it unaltered, remaining in their latent -45 degree state established in zone 2.
• No 'other' photons are deflected to mirror 22 and therefore no 'other' photons enter +/-45 degree polarizer 26 and none are observed by detectors D4a and D5a in zone 6.
• the 'other' photons arriving in zone 6 enter +/-45 polarizer 24 and pass straight through to detector D5b.
• the polarizers are of the thin film beam splitter variety They could, however, be of other varieties, such as Wollaston prism polarizers (Karl Lambrecht part number MW2A-10-5), magnesium fluoride Rochon prisms (Karl Lambrecht part number MFRV-9), traditional 'pile of plates' polarizers, or dichroic plastic polarizing sheet pola ⁇ zers (International Polarizer part number IP38)
• the signal modulating polarizer, H-V polarizer 20 could be replaced by an electro-optic device which can be controlled to either deflect the 'other' photons through an H-V polarizer or to pass them unaltered, or by other active pola ⁇ zation altering components, such as a Kerr cell or a Po
• H-V polarizers 18 and 20 and the mirrors 22 and 23 may be replaced by suitably arranged quarter wave plates which randomize the polarization probability distribution of the photons passing through them
• polarizer 16 and detector D3 can be eliminated from the apparatus without altering the probability distribution of the 'one' photons and the dependency of that distribution on the presence or absence of the zone 5 'other' polarization randomizing element (polarizer 20 or a quarter wave plate in that position)
• This simplified apparatus is illustrated in Figures 3 and 4
• Figure 3 illustrates a simplified embodiment of the invention in which most of the optional elements have been removed and the H-V polarizers 18 and 20 have been replaced by quarter wave plates 32 and 34, respectively
• the function of quarter wave plates 32 and 34 is the same as the function of H-V polarizers 18 and 20, both optical devices randomize the observable +/
• zones 1, 2, 3 and 4 of Figure 3 are the same as shown in the same zones of Figures 1 and 2 'One' photons leaving zone 4 enter into zone 5 where they pass through quarter wave plate 32, which is aligned so as to convert their linear polarization state into a circular polarization state
• Circularly polarized light has a fifty percent probability of passing through a linear pola ⁇ zer of any orientation, circularly polarized light has no latent linear polarization state 'Other' photons leaving zone 4 pass through quarter wave plate 34 in zone 5, also becoming circularly polarized
• zone 6 the circularly polarized 'other' photons enter +/- 45 degree polarizer 24 and are deflected with equal probability to detectors D4b and D5b
• the observation of each 'other' pair photon constitutes a correlation event, setting their corresponding 'one' photons to perpendicular polarization states with equal probability of +/- 45 degrees
• the 'one' photons then pass into zone 7 where they are deflected by +/-45 degree polarizer 28 to detectors D6a and D7a
• the observed probability distribution of the pair 'other' photons at detectors D4b and D5b is (0 125, 0 125)
• the probability distribution of the 'one' photons at detectors D6a and D7a is also (0 125, 0 125)
• the portion of the apparatus from zone 1 through zone 4 and including the 'one' path quarter wave plate in zone 5 is enclosed by a dashed box in both Figures 3 and 4 All of the elements within this box can be considered to constitute a prepared state correlated photon source, 36, which provides correlated photons in prepared quantum probability states to the remaining 'one' and 'other' optical elements
• the remaining 'one' apparatus, polarizer 28 and detectors D6a and D7a, and the remaining 'other' apparatus, quarter wave plate 34, polarizer 24, and detectors D4b and D5b can be located at any convenient distance from the prepared state correlated photon source 36, providing that the optical path length from source 10 to 'one' polarizer 28 is greater than the optical path length from source 10 to 'other' detectors D4b and D5b
• Figure 4 is identical to Figure 3 except that 'other' quarter waveplate 34 has been removed The result is to leave the pair 'other' photons in zone 5 with the -45 degree latent polarization they attained in zone 2 When these pair 'other' photons are observed by detectors D4b and D5b m zone 6 they cause their 'one' pairs to correlate to a +45 degree polarization state The observed probabilities for the 'other' and 'one' photons are thus changed to (0 0, 0 25) and (0 25, 0 0), respectively, which change in probabilities again constitutes a signalling event
• Figures 5 and 6 illustrate the use of these methods with a Type I, parallel polarization correlation, correlated photon source 38
• the arranegment of optical elements is identical in Figure 5 to that of Figure 3 with one exception, +/- 45 degree 'one' path polarizer 14 has been rotated so as to deflect +45 degree polarized photons to detector D2 and to pass -45 degree polarized
• optical elements enclosed by the large dashed-line box in both Figures 5 and 6, labeled 40 constitute another form of a prepared state correlated photon source, driven in this case by a Type I correlated photon source 38.
• the non ⁇ local quantum correlation connection sets the latent polarization state of the corresponding 'one' photons to the same +45 degree polarization state. It is these single 'one' photons which are extracted from the 'one' path by polarizer 14.
• the observed probability distribution of the 'other' and the 'one' photons is the same for Figure 5 as for Figure 3, (0.125,0.125) for both 'other' and 'one'.
• Figure 6 illustrates the signaling state for a Type I source which is equivalent to that of Figure 4 for a Type II source.
• Polarizer 14 is in the same position as in Figure 5, and it serves the same function as in that Figure.
• the 'other' quarter wave plate 34 is removed, allowing the -45 degree state of the 'other' photon to be passed on to detector D5b, setting the polarization state of the corresponding 'one' photons to -45 degrees.
• the observed probability distribution is now the same for both paths in this figure, (0.0,0.25). Note that the probability distributions of the paths of Figure 4 were not identical, but opposite each other.
• my invention is suitable for a variety of correlated quantum objects including also bosons, fermions, and atoms.
• Any source of quantum objects is suitable for my invention provided the source produces correlated quantum objects.
• the controlling means described above, particularly described as beam splitters, or a quarter wave plate may be replaced by any suitable spin selection device which may be employed to select a desired quantum state probability distribution of the quantum objects to be observed.
• suitable spin selection devices include, not only polarizing beam splitters, but also Nichols prisms, wave plates, Kerr cells, Pockels cells, polarizing plastic sheet material and Stern-Gerlach spin analyzers.
• Suitable types of detectors for detecting or making an observation of the quantum state of one or both of the pair of quantum objects include micro channel plates, scintillation detectors and Faraday cups.

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• 1997
  • 1997-03-18 JP JP09533640A patent/JP2000515642A/ja active Pending
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