1. A method for quantum key distribution comprising:
a) providing pulses of coherent light having a time spacing T between adjacent pulses at a transmitter;
b) phase modulating the pulses randomly at the transmitter such that each adjacent pair of pulses is either in phase or out of phase, wherein the modulation applied to each pulse is recorded to provide modulation times;
c) adjusting the intensity of the pulses such that an average number of photons per transmitted pulse is a predetermined value \u03bc less than unity;
d) transmitting the pulses from the transmitter to a receiver over a channel having a transmittance \u03b1;
e) demodulating the received pulses by passing them through a two arm interferometer having a time delay difference equal to T, wherein the interferometer has two outputs (O1 and O2), each output having a corresponding detector (D1 and D2);
f) detecting demodulated pulses with the detectors to provide detection events, each detection event having a detection time, wherein detectors D1 and D2 have quantum efficiencies \u03b71 and \u03b72 respectively;
g) providing the detection times to the transmitter;
i) comparing the detection times to the modulation times to deduce at the transmitter which of the detectors in the receiver is associated with each of the detection events;
wherein a secure key generation rate Rs is a predetermined function of at least \u03bc, \u03b1, \u03b71 and \u03b72;
wherein Rs takes on a maximum value Rmax for an optimal average number of photons per bit \u03bcopt;
wherein \u03bc is predetermined such that Rs is greater than about 0.5 Rmax.
2. The method of claim 1, wherein \u03bc is predetermined such that Rs is greater than about 0.8 Rmax.
3. The method of claim 1, wherein said detectors have equal quantum efficiency \u03b7.
4. The method of claim 3, wherein td is a dead time of said detectors and wherein a sifted key generation rate Rng is given by Rng=(\u03bc\u03b1\u03b7T)exp(\u2212\u03bc\u03b1\u03b7td2T).
5. The method of claim 4, wherein said predetermined function is given by Rs=Rng(1\u22122\u03bc(1\u2212\u03b1\u03b7)).
6. The method of claim 3, wherein said detectors have a dark count rate d and wherein Rs is a predetermined function of at least \u03bc, \u03b1, \u03b7 and d.
7. The method of claim 6, wherein td is a dead time of said detectors and wherein a sifted key generation rate Rng is given by Rng=((\u03bc\u03b1\u03b7+2d)T)exp(\u2212(\u03bc\u03b1\u03b7+2d)td2T).
8. The method of claim 7 wherein said predetermined function is given by Rs=Rng(1\u22122\u03bc(1\u2212\u03b1\u03b7)).
9. The method of claim 7 wherein said system provides a baseline error rate b and wherein a sifted key error rate e is given by
e
=
b
\u2062
\u2062
\u03bc
\u2062
\u2062
\u03b1
\u2062
\u2062
\u03b7
+
d
\u03bc
\u2062
\u2062
\u03b1
\u2062
\u2062
\u03b7
+
2
\u2062
\u2062
d
.
10. The method of claim 9, wherein an error correcting algorithm provides a correction factor f(e) to the Shannon limit, and wherein said predetermined function is given by Rs=Rng(1\u22122\u03bc(1\u2212\u03b1\u03b7)\u22122e+f(e){e log2e+(1\u2212e)log2(1\u2212e)}).
11. A system for quantum key distribution comprising:
a) a source of coherent light pulses in a transmitter, wherein a time spacing between adjacent pulses is T;
b) a phase modulator in the transmitter and capable of modulating the pulses such that each adjacent pair of pulses is either in phase or out of phase, wherein the modulation applied to each pulse is recorded to provide modulation times;
c) an intensity adjuster in the transmitter and capable of adjusting the intensity of the pulses such that an average number of photons per transmitted pulse is a predetermined value \u03bc less than unity;
d) a channel having a transmittance \u03b1 on which the pulses are transmitted from the transmitter to a receiver;
e) a two arm interferometer in the receiver having a time delay difference equal to T and having two outputs (O1 and O2), wherein the interferometer is capable of receiving the pulses from the channel and providing demodulated pulses at outputs O1 and O2;
f) two detectors (D1 and D2) coupled to outputs O1 and O2 respectively, wherein detectors D1 and D2 have quantum efficiencies \u03b71 and \u03b72 respectively;
wherein the demodulated pulses are detected by the detectors to provide detection events, each detection event having a detection time;
wherein the detection times are provided to the transmitter;
wherein the detection times are compared to the modulation times to deduce at the transmitter which of the detectors in the receiver is associated with each of the detection events;
wherein a secure key generation rate Rs is a predetermined function of at least \u03bc, \u03b1, \u03b71 and \u03b72;
wherein Rs takes on a maximum value Rmax for an optimal average number of photons per bit \u03bcopt;
wherein \u03bc is predetermined such that Rs is greater than about 0.5 Rmax.
12. The system of claim 11, wherein said channel includes an optical fiber.
13. The system of claim 11, wherein said detectors are selected from the group consisting of photodiodes, avalanche photodiodes, photomultiplier tubes, upconversion detectors, superconducting transition edge sensors, and solid state photomultipliers.
14. The system of claim 11, wherein said coherent light is provided by an optical source selected from the group consisting of a pulsed laser and a CW laser combined with an optical modulator.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. A fluid filled vibration damping device comprising:
a first mounting member;
a second mounting member having a generally hollow cylindrical shape, and situated with a first opening thereof opposed to the first mounting member with an axial spacing therebetween, the second mounting member having a shoulder portion so that a large diameter cylindrical caulking portion is integrally formed at a second opening thereof;
a rubber elastic body disposed between the first mounting member and the first opening of the second mounting member, and elastically connecting the first and second mounting members to thereby fluid-tightly close the first opening of the second mounting member;
a lid member having an annular fixing member, and fixed by caulking fixation to the second mounting member with the annular fixing member press fit into the cylindrical caulking portion to be superimposed on the shoulder portion, to thereby fluid-tightly close the second opening of the second mounting member;
a fluid chamber formed between the rubber elastic body and the lid member, and filled with a non-compressible fluid;
a partition member installed within the fluid chamber, and having an outside diameter smaller than an inside diameter of the cylindrical caulking portion of the second mounting member;
a plurality of engaging projections formed onto the partition member by rising up respective portions of an outer peripheral portion of the partition member in uplift cutout form toward one side of the partition member,
the engaging projections being fit axially inwardly into the second mounting member with the partition member superimposed on the shoulder portion of the second mounting member so that the engaging projections are held in direct or indirect engagement with an inner circumferential surface of the second mounting member, and that the partition member is positioned in an axis-perpendicular direction with respect to the second mounting member; and
a sealing portion disposed to check a flow of the non-compressible fluid through cutout openings left after the engaging projections have been formed and wherein said cut out openings are formed radially inside of the engaging projections.
2. A fluid filled vibration damping device according to claim 1, wherein a periphery of upraised portion of each of the plurality of engaging projections is press punched over a predetermined width to thereby form a punch-out hole surrounding the each of the plurality of engaging projections.
3. A fluid filled vibration damping device according to claim 2, wherein the sealing portion is formed by extending the fixing member inwardly in a radial direction thereof enough to close cutout openings and punch-out holes in the partition member.
4. A fluid filled vibration damping device according to claim 1, wherein the lid member includes a readily deformable, flexible rubber layer bonded by vulcanization at an outer peripheral portion thereof to the fixing member, and a pressure-receiving chamber partially defined by the rubber elastic body and adapted to give rise to pressure variation during vibration input is formed on one of axially opposite side of the partition member, while an equilibrium chamber partially defined by the flexible rubber layer and readily allowing change in volume is formed on an other of axially opposite side of the partition member, the pressure-receiving chamber and the equilibrium chamber being held in fluid communication with each other through an fluid passage formed by at least partially utilizing the partition member.
5. A fluid filled vibration damping device according to claim 1, wherein the lid member includes an oscillating plate disposed spaced inwardly from the fixing member, and a supporting rubber plate elastically connecting the oscillating plate to the fixing member, the fluid filled vibration damping device further comprising: an actuator for actuating oscillation of the oscillating plate assembled supported by the second mounting member, thereby forming on one of axially opposite sides of the partition member a pressure-receiving chamber partially defined by the rubber elastic body and adapted to give rise to pressure variation during vibration input, while forming on an other side of the axially opposite sides of the partition member an oscillating chamber that is pressure-controlled by means of oscillation of the oscillation plate, the pressure-receiving chamber and the equilibrium chamber being held in fluid communication with each other through a fluid passage formed by at least partially utilizing the partition member.
6. A fluid filled vibration damping device according to claim 1, wherein the sealing portion includes a sealing rubber that is compressed between superimposed faces of the partition member and the fixing member.
7. A fluid filled vibration damping device according to claim 1, wherein an elastic body outer sleeve of generally cylindrical shape is bonded to the outer peripheral portion of the rubber elastic body through vulcanization of the rubber elastic body, the elastic body outer sleeve is fitting within the second mounting member with positioned in the axis-perpendicular direction of the second mounting member, a flange is disposed at a peripheral portion of an opening at a first axial end of the elastic body outer sleeve, and the flange is superimposed on the shoulder portion of the second mounting member and fixed caulkwise at the cylindrical caulking portion so that an outside peripheral portion of the rubber elastic body is fixed to the second mounting member, while the partition member and the fixing member are serially superimposed against the elastic body outer sleeve with the engaging projection of the partition member positioned indirectly against the inner circumferential surface of the second mounting member via the elastic body outer sleeve, and with the outside peripheral portion of the partition member supported held between the fixing member and the flange of the elastic body outer sleeve which are respectively caulked directly at the cylindrical caulking portion of the second mounting member.
8. A fluid filled vibration damping device according to claim 7, wherein the outside diameter of the partition member is smaller than an inside diameter of the shoulder portion of the second mounting member.