AU2011203335B2 - A detection arrangement - Google Patents

Abstract

Abstract A detection arrangement comprising: a splitter; a detector, first and second paths being defined between the splitter and the detector and the splitter being arranged to direct an incoming particle along the first or second path depending upon the value of a parameter of the incoming particle; and a manipulation arrangement located on at least one of the first and second paths, so that, if a particle in a superposition of values of the parameter impinges on the splitter and a wavefunction of the particle is directed along both the first and second paths, the manipulation arrangement with act on the wavefunction to allow interference, at or near the detector, between the portions of the wavefunction that were directed along the first and second paths. 273151 I(GHMattersi P7SadAU1 EP 1 825 615 B1 Figure 1 Figure 2 4 m > 1 2 . V IV> Figure 3

Description

AUSTRALIA Patents Act 1990 COMPLETE SPECIFICATION Standard Patent Applicant(s): Remi Oseri Cornwall Invention Title: A DETECTION ARRANGEMENT The following statement is a full description of this invention, including the best method for performing it known to me/us: Description [00011 This invention relates to a detection arrangement and an information transmission arrangement, and in particular to an information transmission arrangement for allowing efficient communication of information. 5 [0002] Swifter transmission of information is desirable in many fields of technology. The ability to transmit information securely is also of great importance in many fields, In particular banking transactions between clearing banks. [0003] The paper "polarization recombining: a new automatic polarization control scheme for heterodyne or homodyne optical receivers" by V. Napasab and T Okoshi discloses an endless (resetting-free) polarization control scheme called "polarization recombining". The system consists of a polarization rotator, a polarization beam splitter, a 900 linear po 1o larization rotator, an endless phase shifter, and a beam combiner. The state-of-polarization (SOP) of the polarization control light is always linear with a fixed inclination angle regardless of changes in the SOP of the input light. Such a characteristic is achieved without the use of a polarimeter which is undesirable In a practical system. This feature is particularly attractive for automatic polarization control implementation in the 90*optical hybrid receiver. A simulated self-homodyne DPSK system experiment for a receiver utilizing this polarization control scheme is also disclosed. 15 [0004] GB2397452 discloses a quantum communication system comprising: an emitter configured to emit a plurality of photon pulses in groups of photon pulses, each group of photon pulses emitted over a group time period, each photon pulse having a probability of containing at most one photon; and a detector comprising gating means configured to switch the detector between an on state and an off state, wherein the detector is in an on state for at least the duration of two photon pulses during said group time period. The system may be used for quantum key distribution in an encryption 20 system. [0005] One aspect of the present invention provides an information transmission arrangement comprising: an infor mation particle source; afilterprovided at afirst location, the filter being configured only to allow particles having a certain value of a parameter to pass therethrough; and a detection arrangement provided at a second location, the detection arrangement comprising a splitter, a detector, first and second paths being defined between the splitter and the detector 25 and the splitter being arranged to direct an incoming information particle along the first or second path depending upon the value of a parameter of the incoming particle; and a manipulation arrangement located on at least one of the first and second paths, characterised by the information particle source being configured to emit particle pairs, so that a first particle in the particle pair is emitted in a first direction, towards the filter, and a second particle in the second particle pair is emitted in a second direction, towards the detection arrangement, and the detection arrangement being operable 30 to distinguish between an incident information particle having a determined value of the parameter and an incident Information particle in a superposition of values of the particle. [0006] Advantageously, the splitter is a polarizing splitter and the parameter of the incoming particle is the direction of polarization of the incoming particle. [0007] Conveniently, the polarizing splitter is arranged to direct particles having a first direction of polarization along 35 the first arm, and particles having a second direction of polarization along the second arm, wherein the first and second directions of polarization are different from one another by approximately 900. [0008] Advantageously, the manipulation arrangement comprises a rotator arrangement provided on the first path and operable to alter the direction of polarization of polarized particles passing along the first path. [0009] Preferably, the rotator arrangement is operable to alterthe direction of polarization of polarized particles passing 40 along the first path by approximately 90*. [0010] Conveniently, first and second rotator arrangements are provided on the first and second paths respectively and are operable to alter the direction of polarization of polarized particles passing along the paths. [0011] Advantageously, the rotator arrangements are operable to alter the directions of polarization of the particles so that the difference between the directions of polarization of particles passing along the paths is altered by 90*. 45 [0012] Conveniently, the manipulation arrangement comprises a manipulation particle source that Is arranged to emit particles in such a way that they may interfere with a portion of a particle wavefunction passing along the first path, to give a resultant wavefunction that has at least a component having a direction of polarization approximately equal to that of a portion of a particle wavefunction directed along the second path by the polarizing splitter. [0013] Preferably, the manipulation arrangement further comprises a further polarizing splitter located on the first path 50 and arranged to direct an incoming particle towards the detectoror in an altemative direction depending upon the direction of polarization of the incoming particle. [0014] Conveniently, the manipulation particle source Is arranged to emit particlestowards the further polarizing splitter, so that particles emitted thereby may interfere with at least a portion of a particle wavefunction that is directed towards the detector by the further polarizing splitter. 55 [0015] Advantageously, the manipulation arrangement further comprises a phase alteration component that is arranged to alter the effective path length of the first path. [0016] Preferably, the effective lengths of the first and second paths are such that, if a particle in a superposition of values of the parameter impinges on the polarizing splitter, a wavefunction of the particle is directed along both the first 2 and second paths and interference occurs between the portions of the wavefunction that were directed along the first and second paths, the interference will be destructive at the detector so no particle will be detected by the detector. [0017] Advantageously, if a particle having a single value of the parameter impinges on the polarizing splitter and is directed along either the first path or the second path, the particle will be directed to the detector for detection thereby. 5 [0018] Conveniently, the parameter is the direction of polarization of a particle, and the filter is a polarizing filter. [0019] Preferably, the Information particle source Is operable to emit particle pairs, one particle In each pair being directed towards the filter and the other particle in each pair being directed towards the detection arrangement. [0020] Conveniently, the filter may be moved between an on-path position, in which the one particle in each particle pair passes though the filter, and an off-path position, in which the one particle in each particle pair does not pass though 10 the filter. (0021] Preferably, the particles emitted by the information particle source are matter particles. [0022] Conveniently, the information particle source comprises a sample of a material having at least a three-level atomic structure, one of the particles of a particle pair being emitted as an electron moves from a first level to a second level within the structure and the other one of the particles of the particle pair being emitted as the electron moves from 15 the second level to a third level within the structure. [0023] Advantageously, a path length of the first path is longer than a path length of the second path, the arrangement being such that, if a particle Impinges on the splitter and a wavefunction of the particle is directed along both the first and second paths, the portions of the wavefunction that were directed along the first and second paths may interfere with one another at or near the detector. 20 [0024] Preferably, the Information particle source is operable to emit pairs of particles whose wavefunctions are en tangled with one another. [0025] Conveniently, the path length from the information particle source to the filter is less than the path length from the information particle source to the detection arrangement. [0026] Advantageously, a pair of path length modules are provided, each of the path length modules having an input 25 and an output and defining a path length therebetween, the path lengths of the path length modules being substantially identical to one another and hidden from an observer of the path length modules, one of the path length modules being placed so that particles travelling from the information particle source to the filter pass therethrough and the other of the path length modules being placed so that particles travelling from the information particle source to the detection ar rangement pass therethrough. 30 [00271 Preferably, the particles emitted by the information particle source are photons. [0028] A further aspect of the present invention provides an arrangement comprising first and second transmission arrangements according to the above arranged so that the filter of the first transmission arrangement Is located near the detection arrangement of the second transmission arrangement, and the filter of the second transmission arrangement is located near the detection arrangement of the first transmission arrangement. 35 [0029] Another aspect of the present invention provides a method for transmitting information, comprising the steps of: providing a filter at a first location, the filter being configured onlyto allow particles having a certain value of a parameter to pass therethrough; providing a detection arrangement comprising a splitter, a detector, first and second paths being defined between the detector and the splitter being arranged to direct an incoming information particle along the first or second paths depending upon the value of the parameter of the incoming particle; providing a manipulation arrangement 40 located on at least one of the first and second paths, so that, if an information particle in a superposition of values of the parameter impinges on the splitter and a wavefunction of the information particle is directed along both the first and second paths, the manipulation arrangement will act on the wavefunction to allow Interference, at or near the detector, between the portions of the wavefunction that were directed along the first and second paths, characterised by the steps of providing an information particle source operable to emit particle pairs, one particle in each pair being emitted in a 45 first direction, towards the filter, and the other particle in each pair being emitted in a second direction, towards the detection arrangement; and moving the filter between an on-path position, in which the one particle in each particle pair passes though the filter, and an off-path position, In which the one particle in each particle pair does not pass though the filter; wherein the detection arrangement is operable to distinguish between an incident particle having a determined value of the parameter and an incident particle In a superposition of values of the particle. 50 [0030] Conveniently, the path length from the Information particle source to the filter is less than the path length from the information particle source to the detection arrangement. [0031] Advantageously, placing the filter In the on-path position is used to communicate a first binary state, and placing the filter in the off-path position Is used to communicate a second binary state. [00321 Conveniently, the method further comprises the steps of: providing a pair of path length modules, each of the 55 path length modules having an input and an output and defining a path length therebetween, the path lengths of the path length modules being substantially identical to one another and hidden from an observer of the path length modules; and arranging the path length modules so that particles travelling from the information particle source to the filter pass through one of the modules and particles travelling from the information particle source to the detection arrangement 3 pass through the other of the modules. [0033] Preferably, the method further comprises the step of providing a second filter and a second detection arrange ment arranged so that the first filter Is located near the second detection arrangement and the second filter is located near the first detection arrangement. 5 [0034] Advantageously, the method further comprises the steps of: receiving, at the location of the first detection arrangement and the second filter, Information from the location of the second detection arrangement and the first filter; and transmitting a confirmation signal to the location of the second detection arrangement and the first filter within a pre set length of time after receiving the information. [0035] Preferably, the method comprises the step of transmitting encrypted Information. 10 [0036] In order that the present invention may be more readily understood embodiments thereof will now be described, by way of example, with reference to the accompanying drawings, In which: Figure 1 Is a schematic view of a set-up wherein photons are Incident on polarising beam-splitters; 15 Figure 2 is a schematic view of a first information transmission arrangement embodying the present invention; Figure 3 is a schematic view of a second Information transmission arrangement embodying the present Invention; Figure 4 is an energy level diagram for an atomic system for use with the present Invention; 20 Figure 5 is a schematic view of an apparatus using the atomic system of Figure 4; Figure 6 is a schematic view of a third information transmission arrangement embodying the present invention; 25 Figure 7 is a schematic layout of a physically secure quantum channel; Figure 8 Is a schematic diagram of a source of spherically-distributed particles; Figure 9 shows a schematic view of the components of a delayed-choice Interference experiment; 30 Figures 1 a to 10c show diagrams assisting in the explanation of interaction-free measurement by repeated coherent interrogation; and Figure 11 shows two space-time diagrams of nearly simultaneous events using two different approaches. 35 [00371 The formalism of Quantum Mechanics when dealing with a many bodied system requires a basis to span the variables of the system. Thus if we have an n-body system we could have a set of base states lx 1 .. xn> for position, physical properties are derived from the wavefunction Il> on this basis. The state of the system evolves by a first order linear differential equation: 40 id V,)HI v) Eqn.1 di 45 [0038] This shows a totally deterministic evolution of the wavefunction, however measurement Is not deterministic and the measurement M and <y*lMly> collapses into one of the elgenstates of the operator M. The EPR 1 paper asked if the formalism of OM was even correct by concocting a scenario of a two bodied system described by a wavefunction y(xl, x 2 ) In which the two particles were separated by a space-like Interval and a measurement performed. It seemed 50 that if the system was solely described by the wavefunction, a measurement of one of the particles would cause a 'collapse ofthe wavefunction'thusseemingto determinethe physical property of the otherdistant particle instantaneously. [0039] Einstein objected, wanting particles to have ascribed classical, objective properties and Special Relativity to be obeyed. Thus OM was seen as incomplete requiring hidden variables much as in a classical coin split down the middle and concealed in two black-boxes: one distant observer revealing 'heads' would know that the other distant 55 observer had'tails' the system already had a state thatthe measurement simply revealed. Other measurement paradoxes such as 'Schr6dinger's Cat' highlighted deep philosophical problems too. [0040] The way out of this quandary according to Bohr 2 and the principle of Complementarity (or Copenhagen Inter pretation) was that one should not speak of unmeasured quantities as though they exist classically; we can only measure 4 complementary pairs of observables that commute, thus Px and Y or Py and X but not Py and X or Py or Y. Aspects of measurement seem to complement each other and indeed place the system In the state permitted by the measurement A glib rephrasing of this in a staunchly logical positivist frame Is that nothing exists unless it is measured. Thus the EPR argument was misguided, In this viewpoint the measured values did not exist prior to measurement and there Is no 5 conspiracy to send information superluminally when the act of measurement and the whole apparatus of measurement Is taken Into account. [0041] Meanwhile QM continued to have great successes and few were troubled by the apparent underlying philo sophical non-objectivity. However some regarded Bohr's position as that of an obscurant and started to wonder if hidden variables existed and if this apparent superluminal communication was a real phenomena In rejection of the EPR view 10 that it wasn't and could not be. Notably Bohm 3 (and de Broglie earlier) wondered if a 'quantum potential' or 'pilot wave' carrying only information could account for QM and place It back In a classical footing with addition of this device. Proofs were found that still required this hidden Information to be sent superluminally and It was natural to wonder if it was real, something that could be tested experimentally. Bell 4

.

5 came up with a simplified EPR arrangement to test the predications of quantum over classical realism, the former causing correlations in the measurements over space-like intervals greater 15 than the classical case. Figure 1 shows the essence of the setup where an entangled source of photons, S is incident on polarizing beam-splitters (PBS) and then detectors picking up the horizontal and vertical photons. 20 |Q,),=- H})V), +|H) |V),) Eqn. 2 [0042] A coincidence monitor, CM can compute the expectation value of the signals at the detectors DH and Dv: 25 E(1, 2) = PH(i, 2) + P(1, 2) - PHv(, 2) PvH, 2 ) [0043] The Bell inequality Is computed, where the primes donate the PBSs at different angles: 30 IE(1,2) + E(1',2') + E(1',2) - E(1,2') 2 Eqn. 3 35 [0044] Noting the following probabilities: Pi(1, 2) = Pvv(1,2) = %cos 2 (91 -82) and Pv(1. 2) = PvH(1, 2) = sin 2

(

1 -82) 40 Where 01 is the angle of PBS1 and 02 is the angle of PBS2 [0045] The expectation computes as: E(1,2) = cos2(0 1 - 02) [0046] Forthe so-called 'Bell Angles' of 01 = 31r/8, 01'= 3r/8 and 02 = ,t4, 02'= 0 the Bell inequality Is violated yielding: 45 I E(1,2) + E(1',2') + E(1',2) - E(1,2')I= 2v2 [0047] Alain Aspect 6 et al performed this and beyond most people's reasonable doubt it is known that a posterior 50 correlations could be discemed to have occurred between photon pair states on measurements. Newer experiments 7 over distances of up to 1 0km seem to make the space-like separation blunt. [0048] It Is currently thought that signalling via this mechanism would be Impossible from the Indeterminacy of quantum measurement -modulation by a polarizer would result In our binary digit and its complement being signalled half of the time Intended. 55 The Apparatus [0049] Naively we cannot have the distant signaller collapse the wavefunction of an entangled photon into horizontal 5 or vertical components and then have the distant receiver measure the complement to set up a scheme of binary communication. The act of measurement is indeterminate so if the signaller wants to collapse to a horizontal state, he will only achieve this half of the time -the signal becomes totally obfuscated in noise. Relativists still sceptical of the Bell Channel are delighted by this limit as it protects their sacrosanct mindset on causality and the scheme of things. 5 [0050] The indeterminacy of measurement can be overcome if we can use the non-collapsed state as a binary digit and either of the collapsed states as the other. Figure 2 shows a source (S) of entangled photons (pairs 1 and 2) as the communication channel. Distance between the polarising modulator and the interferometer is indicated by the double break in the lines showing the photon propagation. A non-destructive measurement 8

,

9 of the photon state by an inter ferometer set up (via polarlsing beam splitter, PBS) will distinguish the collapsed and non-collapsed states. 10 [0051] Since the horizontal component will not interfere with the vertical component from source both horizontal and vertical arms are rotated about the z-axis by a Faraday rotator or similar to bring them into diagonal alignment. To signal a binary 0 an entangled photon is sent via the communication channel. This achieved by making the distant polarising filter transparent. At the Interferometer the incident photons are set with a destructive interference length to give minimal signal. Binary 1 occurs when the filter is either horizontal or vertical such that un-entanglement Is transmitted and 15 maximum signal occurs at the detector because there is no destructive interference. Note that the interferometer is at a greater distance from the source than the modulator. (0052] in reality a several factors will make the probabilities deviate from the Idea: emission of un-entangled photons from the sources, imperfect optics and imperfect path lengths though it is an easy matterto amplify the difference between these two signals to achieve discrimination of the binary states. Note that at the instant of transmission photons are 20 already present at the modulator and the detector -the signal is not transmitted by mass-energy only the quantum state is being transmitted. Also the state is not being copied so the "no cloning theorem" does not apply 1 . [0053] In general the probabilities calculated will only be very slight modulations in the output signal of the detectors for several reasons: most of the photons will not be entangled (only 1:1010 from a typical down conversion process) and the optics and path lengths will be less than ideal. So the signal will'rlde on top' a large bias signal carrying no information 25 but AC coupling from the detector to an amplifier can begin to discriminate this. Several tens of photons are sent per bit to allow for path differences between the two arms of the interferometer and accurate interference. [0054] Another embodiment is described below with reference to Figure 3. [0055] Since the horizontal component will not interfere with the vertical component from source (A) we regenerate the horizontal photon by entanglement with another source 9 (B) via PBS 2. For convenience source (B) has the same 30 power as source (A). On taking the tensor product of lH 2 > (delayed) and source (B), an entangled vertical photon is generated which therefore contains information sympathetic to channel/source (A). Phase information is shown on the state vector so that interference can occur at the detector. Note the un-used horizontal photons extant from the second PBS must be allowed to travel on in space untroubled least entanglement is lost before detection. [0056] To signal a binary 0 an entangled photon is sent via the communication channel A. This achieved by making 35 the distant polarising filter transparent. At the interferometer aspects of the incident photons (sources A and B) conspire to give minimal signal. Binary 1 occurs when the filter is either horizontal or vertical such that un-entanglement is transmitted. [0057] On detection the following (ideal) probabilities and hence signal strengths at the detector is noted: 40 P, = P(Horizontal + Vertical) =P V + ) ,! ) 45 1+ e" - ' e" i 45 f2 P5 = P(Horizontal)+ P(Vertical =P= P |V + el +P +IVX 4!17) 2 ,y 2 ;' )2r22 551 1+e'e"' 1 1+e i . 2 r2 2 .2 2 6 [0058] In general Po # P 1 by adjustment of the phase 8. A Faraday rotator can be used on the horizontal output from PBS2, as another option, to allow it to interfere with the second arm through the interferometer. In reality a several factors will make the probabilities deviate from the Ideal: emission of un-entangled photons from the sources, imperfect optics and Imperfect path lengths though it is an easy matter to amplify the difference between these two signals to achieve 5 discrimination of the binary states. Note that at the instant of transmission photons are already present at the modulator and the detector - the signal Is not transmitted by mass-energy only the quantum state is being transmitted. Note too that the state is not being copied so the "no cloning theorem" does not apply 10 . [0059] A further method of sending classical data down a quantum channel as elaborated herein is to use Bell Ine qualities relating to position and time as developed by Franson1 4 . This method can favour communication over fibre 10 optic cable for long distances 7 . The essence is to generate entangled photons by a three level atomic system (y1, Y2, yllnd): Depicted in Figure 4 is the energy level diagram for the atomic system. When the system Is energised from the ground state Into state y1 which has a lifetime of r1 a photon y1 Is produced. The system then is In state V2 which 15 has a lifetime of L2 which is considerably shorter than state y1. On measurement of these photons we find that coincidence detection will monitor two events separated by T2 seconds. The probability to detect a single particle is given by (ri detector efficiency): 2oP = (0|V(r~ t(r,t10} Where the photon propagation operator creates a particle from the vacuum state 10> and is given in the Heisenberg representation (constant states with evolving operators) as: . 25 VI(r,t) = eL~/~(~~/ 30 [0060] Consider the apparatus, shown in Figure 5, due to Franson 14 : The source emits the photons y 1 and y2 which arethen collimated by lenses L 1 and L 2 and then filtered (F 1 and F 2 ) so that only photons 1and72 getthrough respectively. Half silvered mirrors M, and M 2 allow the photons to travel along longer interference paths L 1 and L 2 respectively as well as shorter paths S 1 and S2 to detectors D1, D 2 and D' 1 and D' 2 . 35 [0061] Consider first the signal atthe detectors D 1 and D 2 coincidence detection of the two photons is then represented by: 40a = ±T2(0 (r,,t)Vv(r2,t

)

0 ,(r.,t)yv(r 2 ,z'±AT O) [0062] If the time offset window AT is considerably greater than T 2 then this figure tends to zero as is to be expected. On insertion of the silvered mirrors to include longer paths L 1 and L 2 and phase shifts 41 and 02, the wavefunction at the detectors is (for particle one): 45 y(r,)= !yi(r,t)+e yi'(r 1 -AT) 22 50 [0063] Franson is then able to derive the coincidence count between detectors D 1 and D 2 in this scenario with the Interference paths as: 55 R( lR Cos$ -#_2) 4 7 [0064] This is a Bell inequality once again showing non-local effects: the phases 01 and 02 set at space-like intervals are instantaneously controlling the coincidence count. Intuitively this can be understood in the following manner: when the photons y1 and 72 are produced they are entangled and share an uncertainty in time and space for the detection (and hence interference lengths in an interferometer) of (TI + T 2 ) for both photons as this is the lifetime of the states W, 5 and W2. Detection (measurement) of the first photon y1 will guarantee detection of the second photon 72 in the much shorter time frame of [2. Setting up a self interference path such as L 2 will measure this change In the coherence length of the wavefunction. [0065] To implement the scheme of sending classical binary digits down a quantum channel as set out herein using this particular method of space and time correlation of wavepackets the apparatus shown In Figure 6 Is noted: 10 (00661 The protocol once again is that a binary zero Is represented by the act of no modulation (M) and binary one by collapse of the joint wavefunction between y 1 and 72. The modulator is an absorber and can be an electronic shutter made from a Kerr or Pockels cell arrangement. The bit time is longer than the transit time through the interferometer. The lifetime of the second state, W2 is longer than the transit time through the interferometer. (0067] Once again setting the source equidistant between Interferometer and modulator, no information exists prior 15 to the modulator preventing man-in-the-middle attacks. The collapse of the wavefunction and change in the interference length by the measurement of the modulator is reflected in the interferometer acting on the second particle. Interference is set up such that zero modulation results In minimal signal at the detector (destructive Interference) and modulation results in maximum signal (constructive interference). 20 A Physically Secure Quantum Channel [0068] Using two interferometers and modulators depicted in figure 2 a full duplex quantum channel can be set up. This channel is secure against "man in the middle attacks" because the information only exists at the extremities of the channel: any non-coherent measurement would collapse the wavefunction leaving only random noise; coherent meas 25 urement without the correct phase length would yield a constant binary digit as only entangled photons would be perceived. If the phase length could be guessed because the distance between the transmitting stations was well known, tapping into the channel would lead to massive obvious disruption and signal transmission loss; monitoring would catch this breach of security. [0069] Nether-the-less further measures can be made by introducing a secret random phase length at both ends of 30 the channel. The length of fibre optic cable, for instance, would be machine produced in matched pairs in a black box opaque to enquiry (by x-ray, ultrasound, terahertz radiation etc.) such that even the installer of the channel would not know the phase length. A security seal system too would destroy the apparatus If it was not Inserted Into the correct machinery of the communication channel but say time domain reflection equipment to ascertain the secret phase length. A secure docking procedure would do this. 35 [0070] A further aspect of the protection by the random phase length device would be if the eavesdropper was to guess a longer length as information exists after the modulation distance but not before. A periodic acknowledge-protocol within the permitted time frame of the channel phase length and the random phase length would ascertain that the wrong length has been inserted. Sub-nanosecond resolution would have the resolution to down to centimetres In a total channel length that could be kilometres. Phase lock would be a far from easy task. 40 [0071] Although the channel is quantum in nature, it is being used classically sending bits not qubits and all the conventional encryption measures for a classical digital channel would apply too. This physically secure and classically safe channel (in the sense of not cracking say. RSA codes should all the physical protection procedures be surmounted) is a boon to the transmission of sensitive information such as inter-bank money transfer or military information. Figure 7 shows a schematic layout of a physically secure quantum channel as described above 45 Discussion [0072] An apparatus and argument has been presentedforthe instantaneous transmission of information as an adjunct to Bell's Theory and the Aspect experiments. Naturally there are concems about conflicts with Relativity but it shall be 50 shown that nature always must be sending information superiuminallyto ensure conservation of probability and a rational, consistent view of the universe emerges. Experiments exist already that show the effect of a 'quantum potential 3 that carries only pure Information such as repeated coherent interrogation/non-Invasive measurementwhere the wavefunction feels out the experiment environment without transfer of energy to the object under investigation. Inescapably our view of space-time must be altered in the following presentation. 55 (0073] Conservation of Probability Requires Superluminal Transfer of Quantum State Information [0074] The probability density of a normalised wavefunction in QM is given by the square of the wavefunction: 8 p(r, t) =|lv(r, tf 5 or Jp(r, 4r = 1 10 [00751 If there Is any sense In the concept, probability is conserved and would obey the continuity equation: 15 ap(r)+ V -'j(rt)= 0 at [0076] Where the probability current density j is derived on application of the Schr6dinger equation to the above relations as: 20 2mi 25 [0077] Take a spherical source of particles (figure. 8) emitted slowly enough to be counted one at a time. Arranged on a sphere one light-year in diameter (say) is a surface of detectors. Only one particle will be counted per detection event as the light-year diameter wavefunction collapses (becomes localised) randomly so that probability is conserved. The wavefunction, in current thought, Is not perceived as something that is 'real' but is then discarded and a classical 30 path is ascribed from the source to the detector that registered the event to say the particle, retrospectively went along that path. [0078] There is however a problem of discarding the literality of the wavefunction and trying to apply classical concepts before measurement as exemplified bythe delayed choice interference experiment (figure 9). Photons enterthe apparatus incident on a half silvered mirror A. Two detectors 1 and 2 can elucidate what path the photon took as it came Into the 35 apparatus. A second half silvered mirror B inserted into the apparatus can cause the paths to interfere. if the interference length is set so that registry of a photon must mean that both arms of the interferometer were traversed, then this leads to a problem in the classical mode of though If once again we can expand the apparatus to gigantean proportions. Classically the photon (or particle) went along either arm but not both; the decision was made at mirror A. If the arms of our apparatus are light-years across, then Inserting mirror B after the photon has entered the apparatus seems to be 40 determining what path the photon went along or whether it decided to act as a wave and use both arms after it entered this apparatus. [0079] Current thought, not really taking the truth of the wavefunction's physical existence gets Into knots trying to explain these phenomena. We have seen the obfuscation of the Bohr/Copenhagen view where the photon doesn't really exist until it is measured -though something must have been travelling through space. The Many Worlds explanation 45 needs a separate universe at each detection event scenario so that the Schrdinger equation is always obeyed at measurement. Another idea (working with one universe) is that the detector that registered the event sent Information back to the first mirror to determine what path to take; this is the advanced and retarded wave formulation. The trouble here is with the delayed choice experiment -information went back in time in this viewpoint. [0080] It Is reasonable to apply Occam's Razor to Interpretations of this quantum measurement process and admit in so all simplicity, that nature is 'feeling' out the measurement environment across the whole of the wavefunction and is sending information supeiuminally. Thus in figure 7 the wavefunction Interacts with the surface of detectors on the light sphere and conspires so that only one particle per event Is recorded thus probability is conserved. Similarly In figure 9 the wavefunction traversed the apparatus and was incident on mirror B and the detectors to insure a consistent result. [0081] We suggest that nature has a scheme of keeping Its state variables In check by superluminal transmission so 55 concepts such as 'conservation of probability' aren't violated. The next section looks at interaction free measurement where an object can be imaged without, in the limit, photons being incident on it because it is interrogated by the wavefunction. 9 Interaction Free Measurement by Repeated Coherent Interrogation [00821 The picture that is being formed in this paper is the primacy of the wavefunction as a real object in physics and what the effect of Its ability to communicate superluminally does to the current state of understanding of space-time In 5 physics. The real world physical effects of the wavefunction cannot be questioned because of the field of quantum non Invasive measurement 8 9 . The essence of this Is shown In the diagrams below: Figure 1 Ca shows an interferometer set up where a coherent photon source enters at the first beam splitter (partially silvered mirror) and recombines at a second. The detector D-Dark has its coherence length set so that the beams 10 interfere destructively whilst the detector D-Light is set for constructive interference. In figure 1 Ob an opaque object Is placed In one arm of the Interferometer. The firing of D-Dark Indicates that a photon traversed the apparatus without interfering -that Is it came down one arm only. Half of the time a photon will be absorbed by the object and the other half it will pass through to the detectors. We can say that the object has been detected with only half the Incident number of photons Into the measuring- apparatus. Although beyond the scope of this paper figure 1 Oc 15 shows 8 the set up where by repeated coherent interrogations this 50% limit can be bettered and in the limit lead to no photons being absorbed by the object [0083] The 'trick' here is that although the beam splitter, rotator and mirrors give a very low probability for the photon to enterthe side arm with the object (S is very small, sin 2 8> 0 in side arm, whilst main arm Is cos 2 8> 1), the wavefunction 20 always gets through, it Is not attenuated (no potential barrier), we have y = sin 8 not say y = Asin 8 where A would be some attenuation factor. The wavefunction always measures the environment and can be made to traverse the apparatus many times not the photon, giving a vanishing probability of photon interaction with the object but growing certainty of its presence. The lowest mirror switches out the interrogating wavefunction after a number of transits. A detector at a set Interference length can work out if the side arm Is blocked by the count of the detected photons. 25 Simultaneity in Space, Simultaneity in Time (0084] The Lorentz Transform can be understood to have terms amounting to the transit time of light signals: 30 Vt'y and Vx'y/c 2 . The whole Lorentz group is then viewed as a rotation in the space-time of hyperbolic geometry. Absolute time and space concepts are gone; this is our view of 'reality'. What we say is that the physics is correct for light-speed signals (no change therel) but a better system of time measurement can be constructed with clocks using the Bell Channel. We suggest the transformation, x=x'y and t=t'y which can't be used to do physics (things respond to retarded potentials for instance) but is philosophically correct. 35 [0085] Figure 11 shows two space-time diagram views of events very nearly simultaneous in time by a superluminal signal over a space-like interval with event A proceeding B. The Lorentz view gets causality wrong, whilst the 'expand and contract' view of the axis gets it right. Thus the quotidian (3 space + 1 time) view of objective reality Is restored to space; events happen at a definite place and time agreeable by all observers -the Universe is a definite, objective stage 40 in which the theatre of events occur. There is no need for an unknowable preferred reference frame in which simultaneity is preserved as Bell suggested - all observers can agree with this scheme and this was originally suggested by Lorentz in 1904 before reason was lost. Quantum Reality 1: Schr6dinger's Equation in 3-Space 45 [0086] Superluminal effects and the physical existence of the wavefunction force us to change our view about space time. What emerges Is the primacy of movement in 3-space below the speed of light of the wavefunction with length and time dilation effects. The wavefunction carries information about a quantum particle through space to interact with other quantum systems such as the measuring device. We say something is a particle when it has been measured and 50 regular concepts such as energy and momentum are ascribed to it. This classical Intellectual baggage has us thinking in terms of particles moving through space when we really should be thinking in terms of the wavefunction as the primary concept. Operations on it such as yyty*E y define physical observables of the system from the Information and hence the physics. [0087] Indeed to bridge the gap between the classical and quantum worlds, textbooks ease our mind by showing us 55 that In the classical limit where the action is large we get the geometric limit of particular paths and classical mechanics, thus the ray equation or the Hamilton-Jacobi Equations: Solving the Schr6dinger Equation for a single particle in three dimensions we obtain an approximation: 10 ip = Feh Eqn. 4 5 [0088] Where the phase A Is a real function of co-ordinates that will be identified with the classical action and F is a real or complex function independent of time. Due to the smallness of h very rapid changes in phase result in this function over small distances; thus the wavefunction far away from the path of least action rapidly Interferes and decays giving 10 the notion of a classical path In the limit. Substitution of equation 4 in the Schrodinger Equation yields: [.-(V'A)+V+OAF-- 2FVA+2 " + -- -+ - - LV 2 F=0 Eqn. 5 15 2m' atj 2m 8xax y y 8 z 2m [00891 By decreeing classical mechanics and letting h-+0 which is equivalent to the wavelength going to zero, the 1st and 2 nd order terms dropout yielding: 20 i v2A)+V+ = Eqn. 6 25 [0090] Which on the assumption that the wave Is monochromatic and that: A(x,y,z,1)=S(x,y,z)-ha 30 = S-Et [0091] On substitution in equation 6 we obtain a form of the Hamilton-Jacobi Equation: 35 |gradSI =2m(E - V [0092] Somehow the quantum effects are wished out of view and we are furtherfeatherbedded by the idea of a particle in space being represented as a wave packet whose composition is given by the spectral Fourier coefficients. This 40 applies when the particle has been measured and Its position and momentum fall in a narrow range governed by the Uncertainty Principle such that a wave packet results. The situation In figure 7 Invalidates this wave packet view point because the wavefunction is given by a spherical wave, eik.r/r before measurement. It is only after detection that we ascribe position and momentum to a particle concept. [0093] Really it Is the wavefunction that travels through space, furthermore in figure 4 the wavefunction conspires with 45 all the detectors such that conservation of probability is always true: if one photon is measured at one place at one time, it can be measured nowhere else. it is easier to apply Occam's razor to all the formulations of this measurement problem such as the Many Worlds, Advanced-Retarded Waves (the pre-cognisance of the measurement - even information travelling backwards in time from the future) and admit In all simplicity that all the detectors have been superluminally connected by the wavefunctlon with passage of Information such that only one photon per instant is measured. 50 [0094] It Is convenient for the mind to show quantum mechanics as approximating classical mechanics. Via classical mechanics we derive our concepts of space and time, though we should stop trying to do this and face the quantum reality of the wavefunction moving through 3-space. Things exist at macroscopic level that can never be explained classically such as ferromagnetism, superconductivity, the shapes of molecules and the shapes of crystals and we should admit the same for space and time. 55 Quantum Reality 2: The Measurement Problem and Decoherence [0095] Quantum Mechanics is a description of nature and equation 1 should always be true. However measurement 11 throws the system Into an eigenstate of the measurement operator and assigns a probability to It thus: 5 MyI~u) state= 10 p(M)=(y I MyJ |v) 15 [0096] This is the measurement problem: a non-unitary change from the Schradinger equation to the above. Schr6dinger highlighted this In his famous cat paradox where he showed a microscopic quantum event getting entangled with the macroscopic measurement equipment to magnify this obviously non-classical behaviour to absurd proportions. The result was that the cat was left in a superposition of the dead and alive states to be collapsed by when and by whom? [00971 Some of the philosophical spin offs from this were Bohr's Complementarity/Copenhagen Interpretation, weird 20 mind-body/consciousness effects collapsing the wavefunction, the Many World's Interpretation or advanced/retarded waves and quantum super-determinism in which events in the pre-ordained future affect the present. Applying Occam's Razor to this once again and noting what people are actually seeing in their attempts to construct quantum computers'" and the difficulty of maintaining pure states, the most likely, sane candidate to explain the measurement problem is Decoherence Theory 12

.

13 . 25 [009 8 ] The central tenant of Decoherence Theory is the entanglement of a pure state with the environment and the calculation of the reduced density matrix 30 IV/) = al) + al I) (00991 for the system from the system-environment density matrix. Starting with a simple case, consider a closed two state system described by the following state in two-dimensional Hilbert space: 35 The states 10> and 11> are orthogonal. The most general way for calculating physical quantities In QM is by use of the density matrix/operator, thus: =) 40 giving S= |a,j'IOXo+ a,a|0)(1|+ aa, 1 1)(0+ a 1 rIXlI 45 and the density ma .Eqn. a,a, aj so [0100] The diagonal components give the probability that the system is In either state, the off diagonal components the interference between the states. The expectation of any observable represented by an operator A Is given by the trace over the product of the density and operator matrices: 55 {y{ AIV)=1Tr(pA)= p.A. 12 [0101] The system cannot exist in isolation and through unitary evolution becomes entangled with the environment represented by states leo> and le 1 > which are in general non-orthogonal. On taking the tensor product, the density matrix becomes: 5 p(t)= laoI0)Oleo)(0|@(e, I + aaj0)9|e,)(lj@(eI I to +a a,| 1 1)|e,X01@(e, I + la,11)@|e,( 1 1@(e,I [0102] In principle we cannot know the state of the environment and so we are left taking the reduced density matrx with the environmental states traced out. Orthogonal environment basis vectors leo> and leol> are used thus: 15 (eje,= , (e, Ie,) = cos 0, (e' I e,) = sin 6 20 [0103] The reduced density matrix of the two-state system is given by: s,(t)=Trgp(t)=(e,|p(t)le,)+.(e'-Ip(t)le')0 25 hence p(t)=|Ia.. j |0)(0 1+ aea cos M 0)(11 + a a, cos 01|1)(0|+|Ia, I1l X Eqn. 8 30 [0104] Comparing this with eqn. 7 we see the modification to the coherence terms. The environmental states eo and ei are themselves evolving with time and since the environment is truly vast with many energy states, eo and ei will find themselves orthogonal in a very short period of time 12 , for instance if each state is a function of many variables such as (k 1 ... kN, r,...rN) a change in at least one would lead to a very different wavefunction. Consider this simple example for 35 part of the environment modelled by two particles in a rectangular box of Infinite potential, the wavefunction for one particle is: y = sin xsin y'sinz 40 V/W Vabc sa b ' c [0105] The dimensions of the box are ab,c and taking the orthogonality condition for the two particles 1,2: 45 50 [0106] Soon the wavefunctions are orthogonal - lattice vibrations/thermal relaxation effects will make a,b,c vary con tinuously in time. [0107] Thus after a short time our environmental states become orthogonal and our density matrix tends to: 55 #(t)=Ia012j0)(0|+|ajI|2(1 [0108] That is, a statistical mixture of pure states with no superposition. The whole density matrix evolves in a unitary 13 manner but it Is the act of taking the reduced trace, to that which concerns our system that gives the illusion of wavefunction collapse and non-unitary change.. By the time we open the box, Schradinger's Cat is already dead or still alive. A large statistical sample of such experiments would give the results of the reduced density matrix. We can't say which cat will live or die but only predict statistics exactly analogously to the probability space of a multi-particle problem in classical 5 statistical mechanics. Conclusion [0109] We have discussed a superluminal communication/encryption scheme. The 'Quantum Potential, 3 though pure 10 information and having no mass-energy is real and engineering uses for it ought to be considered. It seems another trick has been squeezed out of nature similar to the amazement a century ago that greeted the Maxwell, Hertz, Marconi and Logle Baird discoveries of sending information, speech and pictures incredibly fast around the globe. Zeilinger et al 8

.

9 have talked about non-invasive measurements where X-rays could be used to image a source without actually (in the limit) Imparting energy to the object - a boon to medical Imaging perhaps. Understanding encryption, preserving it 15 and working with it are crucial too for the burgeoning field of Quantum Computation 11 . [0110] At a fundamental level the process of entanglement of a quantum state with the environment seems to be giving some measure of understanding to this mysterious process and a semi-classical view of quantum mechanics becomes apparent with the wavefunction evolving deterministically by the Schr6dinger Equation, always, as it should. [0111] There is considerable irony here; Einstein disliked Quantum Mechanics for its apparent disregard for Objective 20 Reality (indeterminacy and the measurement problem). Modem formulations of QM view the measurement problem as one of loss of coherency as a quantum system gets entangled with its environmenta l . This is a deterministic process as is the evolution of the isolated wavefunction anyway. Space-time with its denial of place and time really makes the universe a mystery, non-objective and non-classical -just how can we talk of the independent existence of an event if it is dependent on the measurement? The pot is calling the kettle black. Space-time is just a calculation/conceptuallsation 25 tool for effects involving mass-energy moving at or below the speed of light. Quantum Mechanics saves reason and returns the Universe to an objective stage of 3-space and time where simultaneous events and material things too can be said to have occurred or existed at a definite place and time Independent of measurement. Classical 'sentiments' and intuition can return to physics in this way if we accept the primacy of a flow of the quantum state (and all that entails -the quantum rules) as a wave through 3-space and time (with relativistic effects of length contraction and time dilation) 30 instead of a classical particle. [0112] To retum to the figures, Figure 2 shows a signal communication apparatus 1. The apparatus comprises an Information particle sources, which is operable to emit particle pairs having indeterminate but related directions of polarisation. In preferred embodiments while the direction of polarisation of neither particle is determined when a particle pair is emitted, the directions of polarisation of the particles are constrained to be different from one another by 9 0*. It 35 will be appreciated that, formomentum to be conserved, the particleswill be emitted in opposite directions. The information particle source is configured so that a first particle in the particle pair is emitted in a first direction, towards a polarising filter 2, and a second particle in the particle pair is emitted In a second direction, towards a detection arrangements, as will be described below in more detail. [0113] In preferred embodiments of the invention, the particles emitted by the information particle source are photons. 40 [0114] The polarising filter 2 is a filter that allows photons having a particular direction of polarisation to pass. The polarising filter 2 is adapted to be placed in a first position, in which the first particle in each particle pair impinges on the filter, or in a second position, in which the first particle in each particle pair bypasses the polarising filter 2 and continues onwards. The polarisingfilter2 may be moveable between the first and second positions in a short period of time. [0115] The modulation of the polarising filter 2 can be achieved by several means. The path of the first particle can 45 be switched between a transparent and polarized path with a switchable mirror. Alternatively electro-optic components such as Faraday rotators, Kerr and Pockel cells acting as electronic shutters can with the assistance of a polarizing beam splitter split the wavefunction of particle one into two channels, horizontal and vertical with dual synchronised shutters set at the appropriate angle for the horizontal or vertical channels. A shutter on its own works by rotating the plane of the wave and to implement the transparent case to transmit binary zero we must have clear transmission - this 50 could not be done with a single shutter because of its polarizing action when open. [0116] The detection arrangement 3 comprises a polarising beam splitter 4 which is the first component of the detection arrangement that is encountered by an incoming particle. The detection arrangement 3 also comprises a detector 5, which is operable to detect particles of the type emitted by the information particle sources, and to provide an appropriate signal when a particle of this type impinges on the detector 5. First and second paths are defined between the polarising 55 beam splitter 4 and the detector 5, and a particle may travel along either of the paths to reach the detector 5. The polarising beam splitter is arranged so that incoming particles having a first direction of polarisation are directed along the first path, and incoming particles having a second direction of polarisation (which in the present example is preferably different from the first direction of polarisation by 90*) are directed along the second path. 14 [0117] In a preferred embodiment of the Invention, suitable angled mirrors M are provided to guide particles travelling along the paths towards the detector. In addition, first and second Faraday rotators 6, 7 are located on each path so that a particle travelling along the first path has its direction of polarisation rotated by n/4(i.e. 450) and a particle travelling along the second path has its direction of polarisation rotated by -W/4 (i.e. - 450). Alternatively a single Faraday rotator 5 may be located so that a particle travelling along the first path has its direction of polarisation rotated 7/2 (i.e. through 900). [0118] A half-silvered mirror or another suitable device (not shown) Is provided near the detectors to allow particles that have travelled along either of the paths to approach the detectors from the same direction. [0119] The polarising filter 3 is placed slightly closer to the information particle source than the detector 5 is to the particle information sources. Therefore, by the time the second particle In each particle pair reaches the detector 5, the 10 first particle of the pair has either impinged on the polarising filter 2, and so the direction of polarisation of the first particle in the pair (and, therefore, also the second particle in the pair) has been determined, or the first particle of the particle pair has bypassed the polarising filter 2 and the direction of polarisation of the first particle of the pair has not been determined, in which case the direction of polarisation of the second particle In the pair in also indeterminate. The progress of a particle through the detection arrangement 3 either case will now be considered. 15 [0120] In the case where the direction of polarisation of the particle arriving at the detection arrangement 3 has been determined, the particle will pass through the polarising beam splitter 4 and be directed along one of the arms of the detection arrangement 3, depending upon the actual direction of polarisation. Whichever of the paths the particle Is directed along, the particle will arrive at, and be detected by, the detector 5 and the arrival of the particle will cause the detector 5 to produce an appropriate signal. 20 [0121] In the case where the direction of polarisation of the particle arriving at the detector has not been determined, it will be understood that the particle will be in a superposition of polarisation states. On impinging upon the polarising beam splitter 4, a portion of the wavefunction of the particle corresponding to the particle having the first direction of polarisation will be directed along the first path, and a further portion of the wavefunction corresponding to the particle having the second direction of polarisation will be directed along the second path. 25 [0122] As the portions of the wavefunction that propagate along the first and second paths pass through the first and second Faraday rotators 6, 7, the directions of polarisation of the particles corresponding to these portions of the wave function are rotated by n/4 and -7/4 respectively and will therefore be equal. The two portions of the wavefunction will both arrive at the detector 5 and will combine with, and superimpose upon, one another. The relative lengths of the two paths are set so that this superposition will result in destructive Interference at the detector 5, and so no particle will be 30 detected. [0123] The detection arrangement 3 is therefore operable to distinguish between an incoming particle whose direction of polarisation has been determined (by the polarising filter 2 being in the first position when the other particle of the pair reached the polarising filter) and an incoming particle whose direction of polarisation has not been determined (if the polarising filter 2 has been bypassed by the other particle of the particle pair). In the first case, a particle will be detected 35 by the detector 5, and in the second case no particle will be detected. to perform the function of modulator to implement at protocol for classical binary data transmission over a quantum channel, when the polarising filter 2 is rendered transparent, the first particle of each pair remains In the state of superposition of horizontal and vertical components this signals binary zero. When the polarising filter 2 is put into the vertical or horizontal position a measurement will be performed on the wavefunction forthe first particle thatwill render collapse into solely the horizontal orvertical component 40 -this signals binary one. The modulation time should be sufficient for the second particle to traverse the Interferometer apparatus and allow sufficient particles to trigger the detector and ensure a good signal to noise ratio. [0124] The purpose of the Faraday rotators 6, 7 Is to manipulate the portions of the wavefunction corresponding to particles travelling along the first and second paths so that they may interfere with one another. A further example of a manipulation arrangement to fulfil this function will be described below. 45 [0125] Figure 3 shows a second signal communication apparatus 8 embodying the present Invention. Once again the apparatus comprises an information particle source, a polarising filterwhich Is arranged at a distance from the information particle sources and a detection arrangement 9 which is also arranged at a distance from the information particle sources, so that particle pairs will impinge on the polarising filter 2 and detection arrangement 9 respectively. The detection arrangement 9 of the second signal communication apparatus 8 is, however, different from that provided as part of the 50 first, and this will be described in more detail below. [0126] Once again the detection arrangement 9 comprises a polarising beam splitter 4 which is arranged so that Incoming particles having a first direction of polarlsation are directed to the first path and Incoming particles having a second direction of polarisation (different from the first direction of polarisation by 900) are directed along the second path. [0127) The second path simply comprises a suitably angled mirror M to deflect particles ravelling along the second 55 path towards the detector. [0128] The first path includes a phase alteration component 10 through which particles travelling along the first path must pass, and the phase alteration component effectively adds a pre-set length to the effective path length of the first path. The phase alteration component 10 may, for example be a block of glass having a very carefully machined length. 15 [0129] A further polarising beam splitter 11 Is also provided on the first path. In the present example, the detection arrangement 9 is configured so that particles having a horizontal direction of polarisation are directed along the first path (with particles having a vertical direction of polarisation being directed along the second path) and the further polarising beam splitter 11 Is arranged so that particles impinging thereon having a horizontal direction of polarisaton are allowed 5 to pass through the further polarising beam splitter 11, and incident particles having a vertical direction of polarisation are reflected towards the detector 5. [0130] A further particle source 12 Is also provided, arranged to emit particles (of the same type as those emitted by the Information particle source) towards the further polarising beam splitter 11. (0131] In the case of an incident particle having an indeterminate direction of polarisatlon, the portion of the wavefunction 10 of the particle from the information particle sources that travels along the first path is put into an additional superposition with the wavefunction of a particle emitted by the further particle source 12, which will have a component corresponding to a vertical direction of polarisation. This will allow interference at the detector 5 between the portions of the wavefunction of the incident particle that have travelled along the first and second paths. As before, the length of the two paths are chosen so that the two portions of the wavefunction will interfere destructively, resulting in no particle detection by the 15 detector 5. This is achieved by the introduction of the phase alteration component 10 which is located on the first path. [0132] It will therefore be understood that this detection arrangement 9 is also capable of distinguishing between an Incoming particle whose direction of polarisation has been determined and an incoming particle whose direction of polarisation has not been determined. (0133] As discussed above In relation to figure 4, two-way communication can be achieved by using two transmission 20 arrangements in parallel with one another, but arranged for information to be transmitted in opposite directions. [0134] When used in this specification and claims, the terms "comprises" and "comprising" and variations thereof mean that the specified features, steps or Integers are included. The terms are not to be Interpreted to exclude the presence of other features, steps or components. [0135] The features disclosed In the foregoing description, or the following claims, or the accompanying drawings, 25 expressed In their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utillsed for reallsing the invention in diverse forms thereof. [0136] For Chris, Eugene and Farooq. 30 References [0137] 1. A. Einstein, B. Podolsky, N. Rosen. Can Quantum-Mechanical Description of Physical Reality Be Considered 35 Complete? Phys. Rev. 47, 777 (1935). 2. N. Bohr. Can Quantum-Mechanical Description of Physical Reality be Considered Complete? Phys Rev 48, 696 (1935). 40 3. D. Bohm. Wholeness and the implicate order. Routledge and Kegan London (1980). 4. J. S. Bell. On the Einstein-Podolsky-Rosen Paradox. Physics 1, 195-200 (1964). 5. J. S. Bell. Foundations of Quantum Mechanics. Ed. B. d'Espagnat, New York: Academic, 171 (1971). 45 6. A. Aspect, P. Grangier, G. Roger. Experimental Realization of Einstein-Podolsky Rosen-Bohm Gedankenexper Iment a New Violation of Bell's Inequalities. Phys. Rev. Lett. 49, 91 (1982). 7. W. Tittel, J. Brendel, H. Zbinden and N. Gisin. Violation of Bell Inequalities by Photons More Than 10 km Apart 50 Phys. Rev. Lett. 17, 81, 3563-3566 (1998). 8. P. Kwlat, H. Weinfurter, A. Zeilinger. Quantum Seeing in the Dark. Scientific American Nov. 1996. 9. M. Kasevich, P. Kwiat, H. Weinfurter, A. Zeilinger. Interaction-Free Measurement. Phys. Rev. Lett. 74, 24 (1995). 55 10. Z. Zhao, Y. Chen, H. Briegel et al. Experimental demonstration of five photon entanglement and open-destination teleportation. Nature 430, 54-58 (2004). 16 11. M. Nielsen, I. Chuang. Quantum Computation and Quantum Information. Cambridge (2000). 12. W.H. Zurek. Decoherence and the. Transition from Quantum to Classical. Los Alamos Science Number 27 2002. 5 13. H.E. Brandt. Quantum Computation: The Grand Mathematical Challenge for the Twenty First Century and the Millennium. Proc. Am. Math. Soc. (17-18 Jan 2000). 14. J.D. Franson. Bell Inequality for Position and Time. Phys. Rev. Lett. 62, 19 (1989). 17

Claims (31)

1. An information transmission arrangement comprising: 15 an information particle source (S); a filter (2) provided at a first location, the filter (2) being configured only to allow particles having a certain value of a parameter to pass therethrough; and a detection arrangement (3) provided at a second location, the detection arrangement (3) comprising a splitter (4), a detector (5), first and second paths being defined between the splitter (4) and the detector (5) and the 20 splitter (4) being arranged to direct an incoming information particle along the first or second path depending upon the value of a parameter of the incoming particle; and a manipulation arrangement located on at least one of the first and second paths, characterised by: the information particle source (S) being configured to emit particle pairs, so that afirst particle In the particle 25 pair is emitted in a first direction, towards the filter (2), and a second particle in the second particle pair is emitted in a second direction, towards the detection arrangement (3); and the detection arrangement (3) being operable to distinguish between an Incident information particle having a determined value of the parameter and an incident information particle in a superposition of values of the particle. 30

2. An arrangement (1,8) according to claim 1, wherein the splitter (4) is a polarising splitter (4) and the parameter of the incoming particle is the direction of polarisation of the incoming particle.

3. An arrangement (1,8) according to Claim 2, wherein the polarising splitter (4) is arranged to direct particles having 35 a first direction of polarisation along the first arm, and particles having a second direction of polarisation along the second arm, wherein the first and second directions of polarisation are different from one another by approximately 90*.

4. An arrangement (1) according to Claim 2 or 3, wherein the manipulation arrangement comprises a rotator (6) 40 arrangement provided on the first path and operable to alter the direction of polarisation of polarised particles passing along the first path.

5. An arrangement (1) according to Claim 4, wherein the rotator arrangement (6) is operable to alter the direction of polarisation of polarised particles passing along the first path by approximately 90*. 45

6. An arrangement (1) according to Claim 4 or 5, wherein first and second rotator arrangements are provided on the first and second paths respectively and are operable to alterthe direction of polarisation of polarised particles passing along the paths. 50

7. An arrangement (1) according to Claim 6, wherein the rotator arrangements (6,7) are operable to alter the directions of polarisation of the particles so that the difference between the directions of polarisation of particles passing along the paths is altered by 900.

8. An arrangement (8) according to Claim 2 or 3, wherein the manipulation arrangement comprises a manipulation 55 particle source (12) that is arranged to emit particles in such a way that they may interfere with a portion of a particle wavefunction passing along the first path, to give a resultant wavefunction that has at least a component having a direction of polarisation approximately equal to that of a portion of a particle wavefunction directed along the second path by the polarising splitter (4).

9. An arrangement (8) according to Claim 8, wherein the manipulation arrangement further comprises a further polar ising splitter (11) located on the first path and arranged to direct an incoming particle towards the detector (5) or in an alternative direction depending upon the direction of polarisation of the incoming particle. 5

10. An arrangement (8) according to Claim 9, wherein the manipulation particle source (12) is arranged to emit particles towards the further polarising splitter (11), so that particles emitted thereby may interfere with at least a portion of a particle wavefunction that is directed towards the detector (5) by the further polarising splitter (11).

11. An arrangement (8) according to any one of claims 2 to 10, wherein the manipulation arrangement furthercomprises 10 a phase alteration component (10) that is arranged to alter the effective path length of the first path.

12. An arrangement (1,8) according to any preceding claim, wherein the effective lengths of the first and second paths are such that, if a particle in a superposition of values of the parameter impinges on the polarising splitter (4), a wavefunction of the particle is directed along both the first and second paths and interference occurs between the 15 portions of the wavefunction that were directed along the first and second paths, the interference will be destructive at the detector (5) so no particle will be detected by the detector (5).

13. An arrangement (1,8) according to any preceding claim wherein, if a particle having a single value of the parameter impinges on the polarising splitter (4) and is directed along either the first path or the second path, the particle will 20 be directed to the detector (5) for detection thereby.

14. An arrangement (1,8) according to claim 2 or 3, wherein the parameter is the direction of polarisation of a particle, and the filter (2) is a polarising filter. 25

15. An arrangement (1,8) according to any preceding claim, wherein the information particle source is operable to emit particle pairs, one particle in each pair being directed towards the filter (2) and the other particle in each pair being directed towards the detection arrangement (3).

16. An arrangement (1,8) according to any preceding claim, wherein the filter (2) may be moved between an on-path 30 position, in which the one particle in each particle pair passes though the filter (2), and an off-path position, in which the one particle in each particle pair does not pass though the filter (2).

17. An arrangement (1,8) according to any preceding claim, wherein the particles emitted by the information particle source (S) are matter particles. 35

18. An arrangement (1,8) according to any preceding claim, wherein the information particle source (S) comprises a sample of a material having at least a three-level atomic structure, one of the particles of a particle pair being emitted as an electron moves from a first level to a second level within the structure and the other one of the particles of the particle pair being emitted as the electron moves from the second level to a third level within the structure. 40

19. An arrangement (1,8) according to any preceding claim, wherein: a path length of the first path is longer than a path length of the second path, the arrangement being such that, if a particle impinges on the splitter (4) and a wavefunction of the particle is directed along both the first and 45 second paths, the portions of the wavefunction that were directed along the first and second paths may interfere with one another at or near the detector (5).

20. An arrangement (1,8) according to any preceding claim, wherein the information particle source (S) is operable to emit pairs of particles whose wavefunctions are entangled with one another. so

21. An arrangement (1,8) according to any preceding claim, wherein the path length from the information particle source (S) to the filter (2) is less than the path length from the information particle source (S) to the detection arrangement (3).

22. An arrangement (1,8) according to any preceding claim, wherein a pair of path length modules are provided, each 55 of the path length modules having an input and an output and defining a path length therebetween, the path lengths of the path length modules being substantially identical to one another and hidden from an observer of the path length modules, one of the path length modules being placed so that particles travelling from the information particle source (S) to the filter (2) pass therethrough and the other of the path length modules being placed so that particles 19 travelling from the information particle source (S) to the detection arrangement (3) pass therethrough.

23. An arrangement (1,8) according to any preceding claim, wherein the particles emitted by the information particle source (S) are photons. 5

24. An arrangement comprising first and second transmission arrangements (1,8) according to any preceding claim arranged so that the filter of the first (2) transmission arrangement is located near the detection arrangement (3) of the second transmission arrangement (1,8) and the filter (2) of the second transmission arrangement (1,8) is located near the detection arrangement (3) of the first transmission arrangement (1,8). 10

25. A method for transmitting information, comprising the steps of: providing a filter (2) at a first location, the filter (2) being configured only to allow particles having a certain value of a parameter to pass therethrough; 15 providing a detection arrangement (3) comprising a splitter (4), a detector (5), first and second paths being defined between the detector (5) and the splitter (4) being arranged to direct an incoming information particle along the first or second paths depending upon the value of the parameter of the incoming particle; and providing a manipulation arrangement located on at least one of the first and second paths, so that, if an information particle in a superposition of values of the parameter impinges on the splitter (4) and a wavefunction of the 20 information particle is directed along both the first and second paths, the manipulation arrangement will act on the wavefunction to allow interference, at or near the detector (5), between the portions of the wavefunction that were directed along the first and second paths, characterised by the steps of: providing an information particle source (S) operable to emit particle pairs, one particle in each pair being 25 directed towards the filter (2) and the other particle in each pair being directed towards the detection ar rangement (3); and moving the filter (2) between an on-path position, in which the one particle in each particle pair passes though the filter (2), and an off-path position, in which the one particle in each particle pair does not pass though the filter (2), 30 wherein the detection arrangement (3) is operable to distinguish between an incident particle having a determined value of the parameter and an incident particle in a superposition of values of the particle

26. A method according to claim 25, wherein the path length from the information particle source (S) to the filter (2) is less than the path length from the information particle source to the detection arrangement (3). 35

27. A method according to claim 25 or 26, wherein placing the filter (2) in the on-path position is used to communicate a first binary state, and placing the filter (2) in the off-path position is used to communicate a second binary state.

28. A method according to any one of claims 25 to 27, further comprising the steps of: providing a pair of path length modules, each of the path length modules having an input and an output and defining a path length therebetween, the path lengths of the path length modules being substantially identical to one another and hidden from an observer of the path length modules; and arranging the path length modules so that particles travelling from the information particle source (S) to the filter 45 pass through one of the modules and particles travelling from the information particle source (S) to the detection arrangement (3) pass through the other of the modules.

29. A method according to any one of claims 25 to 28, further comprising the step of providing a second filter (2) and a second detection arrangement (3) arranged so that the first filter (2) is located near the second detection arrange 50 ment (3) and the second filter (2) is located near the first detection arrangement (3).

30. A method according to claim 29, further comprising the steps of: receiving, at the location of the first detection arrangement (3) and the second filter (2), information from the 55 location of the second detection arrangement (3) and the first filter (2); and transmitting a confirmation signal to the location of the second detection arrangement and the first filter (2) within a pre-set length of time after receiving the information. 20

31. A method according to any one of claims 25 to 31, comprising the step of transmitting encrypted information. 21