Note: Descriptions are shown in the official language in which they were submitted.
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CONTROLLING CORRELATE~) QUANTUM STATE PROBABILITY DISTRIBUTIONS
BACKGROUND OF THE INVENTION
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
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 notemitted 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. Thus, ~sl-ming perpendicular polarization correlation, if the one
photon is measured to be vertically polarized, then the other photon becomes
horizontally polarized at that moment, no matter how far apart the two photons have
2 o traveled prior to the measurement. The polarization states of the two photons are 100
percent entangled; measurement of the polarization state of one photon determines the
polarization state of the other, but prior to measurement, their polarization states are
indeterminate. In essence, the two photons are parts of the same object; no matter
how far they travel apart from each other, ch~ngin~ the properties of one photoninstantly changes the properties of the whole object, including the properties of the
other photon. The experiments of Aspect, et al., have convinced most quantum
theorists that the polarizations of these correlated photons are non-local; the
polarizations are not predetermined at the time of emission, but are rather condensed
into a particular state at the moment of "observation" of one of them. A. Aspect, P.
Grangier and G. Roger, Phys. Lett. 47, 460 (1981) and 49, 91 (1982). A. Aspect, J.
Dalibard and G. Roger, Phys. Lett. 49, 1804 (1982); Z.Y. Ou and L. Mandel, Phys.Lett. 61, 50 (1988) and 61, 54 (1988).
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Various quantum theorists and experimentalists have addressed the question of
whether the non-locality effects of correlated particles can be employed as the basis for
sending information. The published conclusions of Aspect and others have asserted
that such is not possible. Baggott, Jim, The Meanin . of Quantum Theory, Oxford
Science Publications, Oxford University Press, 1992, pp. 148 - 150; P. Eberhardt and
R. Ross, Found. Phys. Lett., 2, 127 (1989). The logic is that the passage rate of either
stream of correlated photons through its respective polarizer will always appearrandom. What is not random is the correlation of polarization between the two
photons. Since the receiver cannot know the state of the sender's photon, then the
receiver cannot glean information from the photons he receives. The signal and the
noise are, therefore, of equal magnitude.
These conclusions are correct, so far as they go. In the systems which have
been previously analyzed, the correlated photon light source is placed midway between
the sender and the receiver and a single polarizer is considered at each end of the dual
photon stream, one for the sender and one for the receiver, and the coincidence of
photon detection at the sender and receiver, as a function of polarizer angle, is
observed. It does appear to be true that, information cannot be sent by correlation of
photon polarizations by means of such an apparatus designed especially for
coincidence counting.
2 o It appears that prior researchers in this field have assumed that sinceinforrnation cannot be transmitted by polarization correlation using two polarizers and
two or more detectors, then the addition of more polarizers to the system will not
improve matters. It is apparently also generally assumed that once a photon passes
through a linear polarizer its polarization state is fixed.
2 5 I have discovered that additional polarizers, when properly arranged and
controlled, allow the separation of signal information from noise in a correlated photon
system and enable the use of such a system for the tr~n~mis~ion of information. This
end is achieved without the need to perform correlation measurements. Unlike
previous correlated quantum particle communication methods the subject invention3 o does not require that both photons of a correlated pair be sent to the receiver so that
coincidence counts may be performed. In fact, if polarization correlation
measurements or coincidence count measurements are performed, the correlation may
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appear to be random. Furthermore? it is therefore not the state of the photon7 or
quantum object, correlation which is communicated, but rather the state of the
apparatus which is communicated. 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 areconnected by single quantum objects with ends in both locations.
SUMMARY OF Tl~l~ INVENTION
It is, therefore, an object of the invention to provide a means for sending
10 information by control of non-local correlation effects in correlated pairs of quantum
objects.
It is a further object of the invention to provide a means for linking two
physically separated measurement apparatus by means of quantum non-locality effects.
It is yet another object of the invention to provide a means to establish a co-
temporal reference point for two physically separated measurement apparatus.
It is an additional o~ject of the invention to provide a means for sending
information by the tr~n~mi~ion of one quantum object of a pair of quantum objects to
a receiver, the tran~mi~ion of the other quantum object of a pair of quantum objects to
a sender, and to control of the probability distributions of the receiver directed
20 quantum object by means of control of the probability distributions of the sender
directed quantum object.
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
30 underlying philosophy is open to wide interpretation. The most widely accepted
interpretation of quantum mechanics is called the Copenhagen Interpretation. One of
the main tenets of the Copenhagen Interpretation is that the specific properties of a
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quantum object are not fixed until the moment of observation or detection of that
object. Science, Vol. 270, 1 DEC 9~, pp. 1439 - 1440. The experiments of Aspect
and other researchers strongly support that this is true, especially for photons. Aspect
3 papers, Ou & Mandell, Baggott, suPra.
Because of this principle, when quantum particles interact with each other, their
quantum states are entangled and the subsequently measured properties of the particles
are linked, or correlated. Since the original interaction involves the conservation of
energy, momentum, quantum number, or other property, the states of the two particles
must satisfy the appropriate conservation laws when they finally are measured.
o Furthermore, if the properties of each particle are not fixed until the moment of
measurement, the only way that the conseNation laws can be satisfied is if the act of
measurement of the properties of one of the particles causes its correlated particle to
instantly take on the properties consistent with conservation. The Copenhagen
Intel~rt;~a~ion proposes that the act of measurement of one quantum object "collapses"
the superimposed potential quantum states (the Schrodinger wave function) of theother correlated quantum object to the required quantum state.
In the case of correlated photons, their linear polarizations are 100 percent
entangled, either polarized parallel to each other or polarized orthogonal to each other
(Type I and Type II, respectively) according to the manner of their creation, in order
20 for the law of the conservation of angular momentum to be satisfied. It is as though
the photons represent the two ends of a constantly lengthening, perfectly rigid rod.
When one end is twisted to a particular position when that photon interacts with a
linear polarizer, so must the other end imm~di~t~.ly twist its photon.
The second effect employed in this invention involves the specific nature of the25 interaction of quantum objects with spin selection devices. For example, 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
30 photons show a very different view.
The energy of a photon is directly linked to the color of the photon. When
randomly polarized light impinges upon a linear polarizer, approximately 50 percent of
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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 fieldcomponent that was perpendicular to the polarization axis, then the color of that
5 photon would change dramatically. No color change is noted, however, when thisexperiment 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
o theory.
It is commonly known that if a second polarizer, or spin selection device, is
placed in the path of the light after it passes through the first polarizer, the percent of
light passing this second polarizer depends on the angle of its polarization axis with
respect to the first polarizer. If the polarization axes are parallel, virtually all of the
15 light passing the first polarizer will also pass the second. If the polarization axes are
orthogonal to each other, i.e., crossed, or at 90 degrees to each other, almost all of the
light passing the first polarizer will be blocked, or absorbed, by the second polarizer.
The small amount of light which does get through is called leakage, and it is a measure
of the efficiency of the polarizers. High efficiency polarizers have a very low leakage
20 level when crossed, on the order of l/lOth of one percent (Glan-Thompson polarizing
prism Newport part number 10GT04AR.14). It is probably impossible to provide
perfectly efficient polarizers because of photon tur~eling effects.
Referring to a pair of crossed polarizers, their important feature is their
orthogonal polarization axes. For simplicity, let us assume that the first polarizer has a
25 horizontal polarization axis and the second a vertical polarization axis, and that the
polarizers are perfectly efficient. We will assume that prior to encountering the first
polarizer, 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
30 obtained by performing certain operations on the photons.) 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
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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 thepolarizer. 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
5 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.
It is known that undisturbed photons which pass through a horizontal polarizer
10 will not subsequently pass through a vertical polarizer. When the potentiallyhorizontally polarized photon encounters the second, vertical, polarizer, it is absorbed.
The probability of choosing a vertical polarization is virtually zero for a photon first
passing through a horizontal polarizer.
Now the third polarizer enters the experiment. The first polarizer encountered
15 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. Let us assume that in this three polarizer experiment 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
2 o 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 peculiar thing happens when the gate is oriented at an angle which is not
25 parallel to either of the other polarizers. It is convenient to choose the angle of the
gate to be +/- 45 degrees from both the analyzer and the polarizer. 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
3 o 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.
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If 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 proportion of photons which pass each of the polarizing elements is 50
percent, so the probability or proportion of photons which make it all the way through
all three polarizing elements is (0.5 x 0.5 x 0.5) = 0.125, or 12.5 percent. These are
10 the photons that make all of the "right" decisions at each polarizer. The remainder,
87.5 percent, make one "wrong" decision somewhere along the way and get absorbed.
In summary, it is known that certain processes can produce correlated pairs of
quantum objects, such as photons, which have entangled linear polarization;
measurement of the polarization of one photon sets the polarization state of its15 companion to a compatible value. It is also known that the linear polarization of a
photon can be altered, without detection, by causing the photon to make a sequence of
quantum choices as it passes through a series of polarizers.
In light of these teac.hin~s, the above objects of the present invention are
accomplished by providing a method and apparatus for controlling the quantum state
20 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
25 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
30 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. By
such method, information may be selectively transmitted on observation of the
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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 selectively choosing whether to affect an alteration of the quantum
state of the one quantum object which is subsequently observed.
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,
such as spin conserving two photon emission processes including, for example, atomic
cascade and spontaneous emission from atornic deuterium or atomic calcium, and
optical parametric down-conversion processes, including both Type I and Type II spin
correlation processes.
Preferably, the source of the pair of correlated quantum objects provides a pair15 having a randomized quantum state probability distribution. Where the pair ofcorrelated quantum objects is provided without 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
20 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
25 prisms, wave plates, Pockels cells, dichroic polarizing plastic sheet material and Stern-
Gerlach spin analyzers. Preferably, the pair of correlated quantum objects is provided
as a part of separated streams of correlated quantum objects. In the case of correlated
photons, this may be accomplished by use of a device selected from the group
con~i~ting of lenses, prisms, mirrors, polarizing beam splitters and combinations
30 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. In the case of other correlated quantum objects other than photons, this may
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be accomplished by use of devices which are the fi~nctional 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
of the quantum states of the other quantum object may selectively include eitherobserving 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. In addition,
by observing the quantum state of the other quantum object by means of a spin
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.
My invention may be more completely understood by reference to the drawings
and detailed description ofthe pler~lled embodiment provided below.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. l is a schematic illustration of one embodiment of my present invention;
Fig. 2 is a schematic illustration of the invention of Fig. l modified to show
how the sign~lling can be switched;
Fig. 3 is a schematic illustration of an alternative embodiment of my present
2 0 IllVelltlOIl;
Fig. 4 is a schematic illustration of the invention of Fig. 3 modified to show
how sign~lling can be switched;
Fig. 5 is a schematic illustration of a further alternative embodiment of my
invention employing a different source of photons; and
Fig. 6 is a schematic illustration of the invention of Fig. 5 modified to show
how signaling can be switched.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the Figures wherein the reference numerals design~te like
parts, the system and method of the present invention is shown in its preferred
3 o embodiment.
All of the Figures are divided into zones to facilitate their explanation. Figures
l and 2 illustrate the operation of this invention by tracing the polarization states of
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photons emitted from a source, 10, of Type II correlated photon pairs through two
.li~elent 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
5 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. Thus '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
o 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 operations of zone I are performed before those of zone 2, and so
on. A key to the symbols used in the Figures is given below in Table I.
SUBSTITUTE Sl ~_t I (RULE 26)
0JHrR~ ON~ Type 11 correl ted photont oUrrcbeelpnr~o d~l~ec~ed in either the one p-th
Sl _ s2 or the other path havln~ perpendicular polarl2aUon preset~ and ~;
O51 12 oSI~ bein~ constralned lo be rouna in oppo~ile peths upon detecUon. The ~
o S o s pholons are deeenerale Jn trequency snd In the llnear polarlzaUon x
X X state complimentary to their preset polarizaUon state x
1.0 1.0
OTHER~f ~ ~ONE Type I correla~ed pholon source providin~ sienal and idler pho~ons
havine an equal probability ot beine de-ected in either the one path
r Sl 12 sz t 11 or the olher path. havine parallel polari~aUon pre~ets. and
o 51 lo 5 o sl 0 5 being cons~r-ined to be round in opposite p-th- upon detecUon. The
~_~ ~ pho~on~ are degenera~e in trequency and in the linear polsri2aUon
X X state complimentary to their preset polarizaUon state
1.0 1.0
cn ~ +/- 45 decree polarizer
Horizonlal-verUcal polarizer u
~ ~ ~) High et~iciency photon detector r
iT
~ ,f Mirror
m .
m ~ ~iorizontally polarized correlated pair pho-on s~ate and lts assoclated ~
_i ~ 0 125 probability . I
V rUc-lly polari ed corr l-ted pair pho-on ~ate ~nd l-s as~oclated
iTi C3~ 0 125 prob-bili-y
45 degree polarized correlated psir pho-on s--te and it~ ~-sociated
0.25 probabllily
-45 deeree pol-rized correlA-ed pair photon s--te ~nd its ~saoclated
0 0625 probablll~y
Paren hc~es around a photon state or It~ probabillty Indi nte that the
st-k IS 8 sin~le ~ho~on stale; one pho~on ot the correl-led palr ha~ ~'
been observed and the rem~ining photon ha- at-alned the Indlcated
0.0625 pol~ri~tion state
Non-local quanlum correlatlon ven~ ob-erva-ion or the polarizatlon v
~~ state ot Ih other photon ~et- ~he ob-erv-ble ~ate~ or ~t~ one
correlated peir photon
Non-local quantum correlaUon evenl: ob-erva-ion Or the polariz~Uon ~O
<~ sta~e or the one photon ~e-- lhe ob-erv-ble ~-ate- ot Its other
correlaled pair photon
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12
Referring now to Figure 1, a source,~O, 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 of5 correlated pair signal and idler photons which all have an equal probability of being
found in either path, with one pl~relled 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
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 I 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. Thus the signal photons in the 'other'
path are labeled Sl and the idlers I2, while the signal photons in the 'one' path are
labeled S2 and the idlers Il. Sl signal photons are paired with Il idler photons and S2
signal photons are paired with I2 idler photons, but only upon observation of one of
20 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-V) 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
25 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,
indistin~li~h~ble in +/- 45 degree polarization state, and indistinguishable in
3 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
m~int~ining the anonymity of the photons, and it is a requirement for m~int~ining
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observable non-local quantum correlation effects. The correlated photons leaving zone
l enter zone 2 in this uniform, anonymous state.
This invention enables .~ign~ling 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 D1, or passing straight through with a
'latent' polarization of-45 degrees. This is a 'latent' polarization because the photon
0 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.
The photons which are detected by Dl have been observed in a +45 degree
polarization state. According to the Copenhagen Interpretation of quantum mechanics
the observation of these photons collapses the wavefunction of the correlated pair of
photons, effectively instantly materializing the r~m~ining photon in the 'one' path with
a polarization orthogonal to that of the detected photon. The collapse of the
wavefunction by detection of the photon in the 'other' path constitutes a correlation
event, symbolized by >>>, labeled A in Figure l. Bach 'one' photon which has itscorrelated pair 'other' photon detected by Dl attains a polarization of -45 degrees.
These 'one' photons are now single photons, no longer part of a correlated pair of
photons, and this state is symbolized by parentheses around the polarization direction
symbol and probability value.
Those 'one' photons which are still part of a correlated pair remain in an
indeterminite +/- 45 degree state. The r~.rn~inin~ 'other' photons pass through beam
2 5 splitter 12 and leave zone 2 with a latent -45 degree polarization.
In zone 3 the 'one' photons enter polarizing beam splitter 14, which deflects all
of the single photons and half of the rem~ining 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 iother' photons which were paired with the single 'one' photons
were previously detected by detector D1 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, ~ecoming single photons. This is
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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 sing71e photons in the
+45 degree polarization state and paired photons with a latent -45 degree polarization.
5 Upon entering zone 4 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, ret~ining their latent -45 degree polarization state. These
rem~ining 'other' photons are the pairs to the rçm~ining 'one' photons. It can be seen
from Figure 1 that at this point 75 percent of the input photons to each of the 'one'
10 path and the 'other' path have been discarded because one or the other of the photons
of a pair made a 'bad' choice of polarization state. The rem~ining 25 percent of the
input photons made 'good' polarization state choices, making them useful for
sign~lling These are the photons which pass from zone 4 to zone 5.
The paired 'one' photons arriving in zone 5 enter horizontal-vertical (H-V)
15 polarizer 18 and are separated with equal probabilities into rightward deflected
horizontal (H~ photons and downward passing vertical (V) photons. In order to keep
Figure 1 compact the H photons are shown reflecting from mirror 23, which does not
alter their polarization state. The 'other' photons arriving in zone 5 enter H-Vpolarizer 20 and are equally divided into leftward deflected H photons and downward
20 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 bearn splitters 26
25 and 24, respectively, and are detected in definite +/-45 degree polarization states by
detectors D4a, D4b7 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
30 degree polarization states of their pairs in the 'one' path. This is indicated by the
correlation symbol labeled C. Half of the 'one' photons attain a +45 degree latent
polarization and half attain a -45 degree latent polarization. As indicated by the
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parentheses around the polarization vectors, these 'one' photons are now single,having lost their 'other' pair photons.
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 degreepolarization state and detectors D7a and D7b observe the 'one' photons having a -45
degree polarization state.
Of significance is 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
ofthe '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 .sign~lling method. The second state is illustrated in Figure 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, rem~ining in their
latent -45 degree state established in zone 2. No 'other' photons are deflected to
rnirror 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 inzone 6 enter +/-45 polarizer 24 and pass straight through to detector D5b. No 'other'
photons entering zone 6 have a +45 degree latent polarization state, so none aredeflected by polarizer 24 to detector D4b. The observed probability distribution of the
'other' photons, as previously defined, is changed to (0.0, 0.25) when H-V polarizer
20 has been removed.
'One' photons entering zone 5 are processed in the same manner as in Figure l;
3 o they enter H-V polarizer 18 and are equally divided into H and V states, thereby losing
their latent +45 degree state produced in zone 3. In zone 6 the observation of the
'other' photons in a -45 degree state by detector D5b sets the latent polarization state
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of the 'one' photons to a +45 degree state by non-local quantum correlation effects
represented by correlation symbol C. The 'one' photons arriving in zone 7 enter +/-45
degree polarizers 28 and 30 and are detected by detectors D6a and D6b. Since there
are no 'one' photons with a latent -45 degree state, none pass through polarizers 28
and 30 for detection by detectors D7a and D7b. The observed probability distribution
of the 'one' photons, as previously defined, is thus changed to (0.25,0.0). These
changes to the quantum state probability distributions of the "other" and "one"
photons constitutes a si~n~lling event.
It is important to note that no change was made to source 10, nor were any
10 changes made to any of the optical elements in the ' one' path, between the
arrangements of Figure I and l~igure 2. The only change made between these two
arrangements is the inclusion or exclusion of H-V polarizer 20 in the 'other' path. The
'other' path and the 'one' path may be physically widely separated, yet this alteration
of the optical arrangement in the 'other' path will alter the observed probability
distribution ofthe photons in the 'one' path.
Many features of this invention may be altered without materially altering the
ability to affect the observed probability distribution of 'one' photons by manipulating
the observed probability distribution of the 'other' photons by the inclusion orexclusion of polarizer 20. As shown in these Figures, 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 polarizers (International Polarizer part
number IP38). The signal mod~ ting 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 polarization
altering components, such as a Kerr cell or a Pockels cell.
In both Figures 1 and 2 a number of the optical elements are enclosed by
dashed boxes labeled 'OPTIONAL'. If these elements are removed the observed 'one'
probability distribution will be di~lent from that of Figures I and 2 because the
horizontal photons deflected by polarizer 18 will be discarded and will not proceed on
to the 'one' zone 7 detectors. Removal of these elements does not eliminate the
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dependence ofthe 'one' probability distribution on the presence or absence of 'other?
polarizer 20. Removal of these elements also alters the observed probability
distribution of the 'other' photons because both single 'other' photons and paired
'other' photons will be observed by detectors D4b and DSb. With these elements in
s place as shown in Figures 1 and 2 single 'other' photons are 'purified' from the 'other'
path, leaving only paired 'other' photons to be detected by detectors 1~4b and DSb. If
the optional elements are removed from Figure 1 the probabilities for the 'other' and
the 'one' paths are (0.125,0.125) and (0.0625,0.0625) respectively. If the optional
elements are removed from Figure 2 the probabilities for the 'other' and the 'one'
paths are (0.25,0.25) and (0.125,0.0) respectively.
The function of 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. This simplifies the
apparatus by elimin~ting polarizers 18, 20, 26, and 30, mirrors 22 and 23, and
detectors D4a, D5a, D6a and D7a. Furthermore, polarizer 16 and detector D3 can be
elimin~ted 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
S 'other' polarization randornizing 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 +/- 45 degree polarization state of the photons which
2 5 pass through them.
The optical processes and polarization states of zones 1, 2, 3 and 4 of Figure 3are 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 isaligned 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
polarizer of any orientation; circularly polarized light has no latent linear polarization
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state. 'Other' photons leaving zone 4 pass through quarter wave plate 34 in zone 5,
also becoming circularly polarized.
In zone 6 the circularly polarized 'other' photons enter +/- 45 degree polarizer24 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 rPm~ining 'one' and 'other' optical elements. The
rP.rn~ining 'one' apparatus, polarizer 28 and detectors D6a and D7a, and the rem~ining
'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
2 5 degree latent polarization they attained in zone 2. When these pair ' other' photons are
observed by detectors D4b and D5b in 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 sign~l1ing 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
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'one' path polarizer 14 has been rotated so as to deflect +45 degree polarized photons
to detector D2 and to pass -45 degree polarized photons to the following zones of the
apparatus. This is the opposite of the function of polarizer 14 in Figure 3. While this
is the only change in the optical elements, the action of these elements on the
s correlated photons is different because properties of source 3~ requires the photons to
correlate to parallel polarization states instead of perpendicular polarization states, as
in the previous figures.
The 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 photonsource, driven in this case by a Type I correlated photon source 38.
Thus when +45 degree 'other' photons are detected by detector Dl 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 l4. The
observed probability distribution of the 'other' and the 'one' photons is the sarne for
Figure 5 as for Figure 3, (0.125,0.125) for both 'other' and 'one'.
Figure 6 illustrates the .ci~n~ling 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. As in Figure 4 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 sarne 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.
It is important to note that in the methods of all of these Figures, and in any
similar or derivative methods, the specific angles of the polarizers and the resulting
latent polarization states of the photons are not, in themselves, significant. The
significance is in the relationship of each polarizer to the known polarization states of
the photons. Thus, if the apparatus were rotated 45 degrees, the H-V output
3 o polarization states of the signal and idlers from source 10 would become known +t-45
degree polarization states, the H-V polarizers would become +/-45 degree polarizers,
and the +/-45 degree polarizers would become H-V polarizers.
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With reference to Figs. 1-6, I have particularly illustrated the preferred
embodiment of my invention employing photons. Alternatively, 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. Furthermore, 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.
Having now fully described my invention, it will be apparent to one of ordinary
skill in the art that many changes and modifications can be made thereto withoutdeparting from the spirit or scope of my invention as set forth herein.
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