Abstract
A quantum internet that connects remote quantum processors1,2 should enable a number of revolutionary applications such as distributed quantum computing. Its realization will rely on entanglement of remote quantum memories over long distances. Despite enormous progress3,4,5,6,7,8,9,10,11,12, at present the maximal physical separation achieved between two nodes is 1.3 kilometres10, and challenges for longer distances remain. Here we demonstrate entanglement of two atomic ensembles in one laboratory via photon transmission through city-scale optical fibres. The atomic ensembles function as quantum memories that store quantum states. We use cavity enhancement to efficiently create atom–photon entanglement13,14,15 and we use quantum frequency conversion16 to shift the atomic wavelength to telecommunications wavelengths. We realize entanglement over 22 kilometres of field-deployed fibres via two-photon interference17,18 and entanglement over 50 kilometres of coiled fibres via single-photon interference19. Our experiment could be extended to nodes physically separated by similar distances, which would thus form a functional segment of the atomic quantum network, paving the way towards establishing atomic entanglement over many nodes and over much longer distances.
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The data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request.
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Acknowledgements
This work was supported by the National Key R&D Program of China (2017YFA0303902, 2018YFB0504300, 2017YFA0304000), the Anhui Initiative in Quantum Information Technologies, the National Natural Science Foundation of China and the Chinese Academy of Sciences. We thank QuantumCTek for providing the field-deployed fibres.
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X.-H.B. and J.-W.P. conceived the research. Q.Z., X.-H.B. and J.-W.P. designed the experiment. Y.Y., X.-Y.L., B.J., P.-F.S., R.-Z.F., C.-W.Y. and X.-H.B. carried out the experiment with assistance from all other authors. F.M., M.-Y.Z., X.-P.X. and Q.Z. built the QFC module. W.-J.Z., L.-X.Y. and Z.W. fabricated the superconducting nanowire single-photon detectors. Y.Y., Q.Z., X.-H.B. and J.-W.P. analysed the data and wrote the paper with input from all other authors.
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This file contains the following sections: I. General information of experimental setups; II. Phase stabilization; III. Lasers in outdoor application; IV. Analysis on experimental imperfections; V. Entanglement evaluation of Fock state entanglement; and additional references.
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Yu, Y., Ma, F., Luo, XY. et al. Entanglement of two quantum memories via fibres over dozens of kilometres. Nature 578, 240–245 (2020). https://doi.org/10.1038/s41586-020-1976-7
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DOI: https://doi.org/10.1038/s41586-020-1976-7
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Xinhang Shen
As Einstein's relativity has been disproved (see below), we know that there is a fluid medium we call aether existing everywhere in the visible part of the universe. All particles are bathed in aether and will generate aether waves whenever they are moving to produce phenomena of so called the particle-wave duality. Without taking the effects of aether into account, quantum mechanics is wrong too and in nature there are no waves of probability because probability is a mathematical concept not a physical substance and can't vibrate to become waves. Without waves of probability in nature, there is no such phenomenon called quantum entanglement. Therefore, there are no so called quantum communication and quantum computing.
Here is the disproof of special relativity which I have to repeat again and again. I tried to get my paper to be published on Nature and then on Science journals, but got rejected without peer-reviewing and any soundable reasons (they said they don't need to give me any reason to reject my paper). It seems that they reject all anti-relativity papers unconditionally. Therefore, I submitted it to and published it on Physics Essays ( https://www.researchgate.ne... ) - an international peer-reviewed physics journal which seems the only world recognized journal with an open mind. But, many physicists refused to recognize the discovery of the paper because it is not published on authoritative journals (like Nature, Science, etc). The discovery has been published for about four years, but nobody has been able to refute it yet.
The fatal error of special relativity is that it redefines time and space with Lorentz Transformation and equates the newly defined relativistic time with physical time defined by a physical clock, which are two totally different things as shown in the following:
It is known that a physical clock is a physical process such as the rotation of the earth around the sun in which the physical time is recorded by the status change of the process. The status change of a physical process is always represented by the product of the lapse of the theoretical time and its progressing rate divided by a calibrate constant in either Newtonian mechanics or special relativity. That is, the relationship between the theoretical time t and the physical time T measured by a physical clock is: T = tf/k where t is the theoretical time, f is the frequency of the clock and k is a calibration constant. We have to verify that T = t before using a clock to measure the theoretical time.
In Newtonian mechanics, since the theoretical time is the absolute Galilean time and thus the frequency is a frame independent constant. We can set k = f to make T = tf/k = tf/f = t in all reference frames, which means a physical clock does measure the absolute Galilean time, and confirms that our physical time is absolute too. Therefore, Newtonian mechanics is self-consistent in regarding the concept of time.
In order to verify whether the clock time has the same property as the theoretical time in Lorentz Transformation in special relativity, let’s look at physical clocks. If you have a clock (clock1) with you and watch my clock (clock2) in motion and both clocks are set to be synchronized to show the same physical time T relative to your inertial reference frame, you will see your clock time: T1 = tf1/k1 = T and my clock time: T2 = tf2/k2 = T where t is relativistic time, f1 and f2 are the frequencies of clock1 and clock2 respectively observed in your inertial reference frame, k1 and k2 are calibration constants of the clocks. The two events (Clock1, T1=T, x1=0, y=0, z=0, t) and (Clock2, T2=T, x2=vt, y=0, z=0, t) are simultaneous measured with both relativistic time t and clock time T relative to your reference frame. Now we want to see how these simultaneous events will behave after Lorentz Transformation. When these two clocks are observed by me in the moving inertial reference frame, according to special relativity, we can use Lorentz Transformation to get the same events relative to my frame of (x', y', z', t'): (clock1, T1′, x1′=-vt1', y’=0, z’=0, t1′) and (clock2, T2′, x2′=0, y’=0, z’=0, t2′), i.e., I will see T1′ = t1’f1’/k1 = (γt)(f1/γ)/k1 = tf1/k1 = T1 = T and T2′ = t2’f2’/k2 = (t/γ)(γf2)/k2 = tf2/k2 = T2 = T, where γ = 1/sqrt(1-v^2/c^2). That is, no matter observed from which inertial reference frame, the events are still simultaneous measured with clock time T i.e. the two clocks are always synchronized measured with clock time T, but no longer synchronized measured with relativistic time t’. Therefore, clock time and relativistic time behave differently in Lorentz Transformation. The change of the reference frame only makes changes of the relativistic time from t to t’ and the frequency from f to f’, which cancel the change of each other in the formula: T= tf/k and thus makes the physical time unchanged, i.e., clock time is reference frame independent and absolute. Current mainstream physicists in the world do not realize that there are two changes (time expansion and frequency decrease) happened in any moving physical clock and wrongly interpret the slowdown of its frequency as the slowdown of clock time shown on the moving clock, missing the effect of the expansion of the relativistic time of the moving frame. For example, relativists claim that a traveling twin will be younger than the twin staying on earth when he returns to earth because of relativistic time dilation. But relativists don't realize that the biological age of the traveling twin relative to earth is a product of relativistic time and relativistic aging rate, in which relativistic time expands by factor γ and the aging rate decreases by the same factor γ after Lorentz Transformation to make the biologic age as the product be exactly the same. Therefore, there is no biological age difference between the two twins.
All what special relativity does is the introduction of a new definition of time and space as shown in the following.
In Newtonian mechanics, time is absolute and space is rigid, following Galilean Transformation between inertial reference frames (X, Y, Z, T) and (X', Y', Z', T') with a relative velocity v:
T' = T
X' = X - vT
Y' = Y
Z' = Z
where (X, Y, Z, T) is set to be the frame with isotropic speed of light and (X', Y', Z', T') is the frame moving at speed v relative to (X, Y, Z, T).
But Einstein forces space and time to follow Lorentz Transformation which is equivalent to:
In the frame of (X, Y, Z, T):
t = T
x = X
y = Y
z = Z
and in the frame of (X', Y', Z', T'):
t' = T'/γ - γvX'/c^2
x' = γX'
y' = Y'
z' = Z'
You can easily verify that (x, y, z, t) and (x', y', z', t') follow Lorentz Transformation:
t' = T'/γ - γvX'/c^2 = T/γ - γv(X - vT)/c^2 = t/γ - γv(x - vt)/c^2 = (1/γ + γv^2/c^2)t - γvx/c^2
= γt - γvx/c^2 = γ(t - vx/c^2)
x' = γX' = γ(X - vT) = γ(x - vt)
y' = Y' = Y = y
z' = Z' = Z = z
i.e. Lorentz Transformation:
t' = γ(t - vx/c^2)
x' = γ(x - vt)
y' = y
z' = z
We can also see in the new coordinate system i.e. the relativistic coordinate system, the speed of light is
c = x/t =X/T = (X' + vT')/T' = [x'/γ + vγ(t' + vx'/c^2)/[γ(t' + vx'/c^2)] = [γ(x' + vt')]/[γ(t' + vx'/c^2)]
= (x'/t' + v)/(1 + vx'/t'/c^2)
i.e.
c(1 + vx'/t'/c^2) = x'/t' + v
i.e.
x'/t'(v/c - 1) = v - c
i.e.
x'/t' = (v - c)/(v/c - 1) = c
i.e. the speeds of light defined by x/t and x'/t' are the same constant c in all inertial reference frames. Similarly, if you use the speed of sound to replace c in the above, you will get that the speed of sound defined by the new coordinate system is constant relative to all inertial reference frames too. But that does not change the fact that the real speed of sound measured with physical rulers and clocks is not constant relative to all inertial reference frames because clock time won't change with the change of the definition of the theoretical time and still absolute as shown above.
On the other hand, we can use special relativity to prove that the real speed of light measured with physical rulers and clocks still follows Newton's velocity addition formula. In special relativity, we have space and time defined by rulers and clocks:
In the inertial reference frame with isotropic speed of light:
T = t
X = x
Y = y
Z = y
In the other frame moving at v:
T' = γ(t' + vx'/c^2)
X' = x'/γ
Y' = y'
Z' = z'
You can easily verify that (X, Y, Z, T) and (X', Y', Z', T') defined above follow Galilean Transformation.
The real speed of light measured with X'/T' is:
C' = X'/T'
= (x'/γ)/[γ(t' + vx'/c^2)]
= (x'/t')/[γ^2(1 + v(x'/t')/c^2]
= c/[γ^2(1 + v/c)]
= c^2(1 - v^2/c^2)/(c + v)
= c - v
= (x/t) - v
= (X/T) - v
= C - v
That is, even in special relativity, the real speed of light still follows Newton's velocity addition formula, which has denied the postulate of special relativity that the speed of light is constant relative to all inertial reference frames.
Now it is clear that all special relativity does is to redefine time and space. Just like the property of a circle which is always a circle no matter whether you use a cartesian coordinate system or a polar coordinate system, the property of a physical clock is the same (i.e. clock time is always absolute) too no matter whether you use Galilean space and time or relativistic space and time. Therefore, the relativistic time is not clock time but a fake time and so is the relativistic space. Thus, all what special relativity describes is irrelevant to the physical reality.
As special relativity has been disproved and our physical time is absolute, there can be only one inertial reference frame relative to which the speed of light is isotropic. Since the speed of light after going through a lens can recover, unlike the speed of a bullet which will never recover after going through a wall, the speed of light only depends on the medium and thus light should be waves of a medium. Michelson-Morley experiment has denied the existence of a rigid aether, and thus aether must be a fluid. The very inertial reference frame with isotropic speed of light should be the frame moving with local aether similar to the frame moving with local air relative to which the speed of sound is isotropic. As light can exist everywhere in the visible part of the universe, aether should be everywhere too. All electromagnetic phenomena are just the phenomena of aether dynamics. There is no electric field and no magnetic field in nature, but only different flows of aether. So-called electric force and magnetic force are forces exerted by the flows of aether, just like the resistance and lift exerting on an airplane, where there is no resistance field and no lift field, but only air flows. As aether exists everywhere, delivers all electromagnetic forces and plays critically important roles in all physical processes, quantum mechanics, without taking the effects of aether into account, should be wrong too. As every particle is bathed in aether, any motion of the particle will disturb aether and generate waves of aether to make the particle show the particle-wave duality. Thus, there is no probability wave in nature, not to mention the existence of wave function, superposition, entanglement and Schrodinger’s cat. Similarly, there is no such thing called spacetime in nature, not to mention the existence of expansion, curvature, ripples or singularities of spacetime. Thus, general relativity and big bang theory are wrong too.