Not sure what we are talking about? Here are some helpful explanations and extra info about our work and quantum entanglement.
What is quantum entanglement?
Quantum Entanglement is a physical phenomenon where the state of one particle is tied to the state of another, even across great distances. Neither particle's properties, such as position, momentum, spin or polarization, can change without changing the other. Their fates are meshed.
Strange right? It is. In fact, even though this phenomena was observed by Einstein in 1935, he decreed it to be impossible and called it "spooky action at a distance."
What are the particles we entangle?
Most of the particles we work with are photons. A photon is the smallest quantity of energy that can be transported, SO small that it has NO mass. A photon can be described both as a wave and a particle and the same time. Photons are what make up electromagnetic radiation, one form of that radiation being light. These particles are created when an electron in an atom drops to a lower energy state. It gets rid of the excess energy in the form of radiation. A photon can also raise the energy level of an electron.
And photons are fast. Very fast. They are the fastest things known and they can never slow down. They always travel at 299,792,458 meters per second, from birth to death.
To create the entangled photon pairs we need for our experiments, we excite calcium atoms, but forbid them from descending one energy level, instead they must go down two energy levels very quickly, emitting two photons at essentially the exact same time. And, because momentum must be preserved, those sister particles are sent in opposite directions.
How have we observed this quantum entanglement in the lab?
Well, the test is a little hard to understand, but let’s start by imagining a spinning rod.
The rod is so small that we can’t know which way it is spinning until it passes through a sensor where we can measure it. The sensor is shaped something like this, with a slot for the rods to pass through. Only the rods that are at the same angle as our sensor will be able to pass. As the rod is approaching the sensor it MAY turn to fit through the slot.
Each rod has an up and a down. When the rod turns to fit into the slot, depending on the angle of the sensor, it may rotate right or left. If the rod is at a 90 degree angle to the slot it has a 50/50 change of turning to the right or left. But if the angle is smaller, then it is more likely that the rod will turn in one direction.
In order to compare the state of two rods, we will need to create them at the same time, and because the total momentum of the universe must always stay the same, the rods will be sent in opposite directions, with opposite spins. As they pass through the sensors we will see that one is up and the other is down, if they are at the same orientation as the sensor that is.
If they are not at the same angle as the slot in the sensor, then they will have to turn, changing their relationship to each other. Now they may no longer be facing in opposite directions.
If, that is, quantum entanglement did not exist.
Instead what we see is that no matter what, the two rods remain in opposite orientation from each other! They are always flipped! How do they know? We have measured them at great distances, and corrected for human influence, and still the rods remain the opposites of each other while spreading across the universe.
We know that this is not a form of communication between the particles because they are aligned instantaneously, and any kind of reaction from one to the other would have to travel faster than the speed of light.
The Quantum Bell Test:
Einstein thought that if entangled particles must have some way of knowing what their partner particle was doing at all times, but that way couldn’t be communication since the particles were changing in syncrony faster than the speed of light. He thought they had a plan for what way they would turn all the way back to the moment of their birth. It wasn't until 1964 when John Stewart Bell came up with a way of testing this, the Quantum Bell test, that we had a way of proving that the particles could not have a pre-existing plan.
We start out with two particles created at the same moment, each traveling towards a detector. We are going to randomly choose one of three different angles that the detectors could be at, and we will choose these separately so that the detectors could be a different angles from one another. The particles will be forced to be unequally balanced from their partner particle some of the time. We will then record the number of times that the particle’s states were different or the same.
Based on probability equations we know that if the particles had pre-made plans, then they should be opposite to each other 5/9ths of the time or more, while entangled particles should be opposite 50% of the time. After detection, our coincidence monitor will then tell us at what percentage our particles turned in opposite directions.
And we learned, that the particles have no hidden plan because their percentage of samyness is… 50%!
How did Abrahmsson test chain entanglement?
We started by creating a pair of sister particles, A/B. One of the sisters, A, is immediately measured and absorbed, or you could say destroyed. Particle B continues on unmeasured, although we know it’s state, because it must be the opposite of A. While B is still traveling undetected, we will birth our new twins, C and D. C will then be measured at the same exact moment as B is being measured, thus entangling and destroying them. Finally, the last remaining sister D gets detected.
We see from this that these particles are entangled when A and D are destroyed at the SAME time or if one is destroyed before the other. These two particles that have never existed in the same space OR TIME, are entangled, so we know a quantum event could spread both backward and forward across time and be basically unobservable in the material world.
Setting up our quantum network:
We set up two networks at a distance from one another, with one lab in Los Angeles and the other in San Jose.
We started from a very special pair of entangled photons that we named Laura and Rita, after Inderpal and Eleonor’s mothers. We trapped those photons each in their own custom made cavity where they could bounce around for a long time. We then took a two level atom, starting with it at the lower level, and introduced it into the cavity. It absorbed the photon, bounced around, radiated the photon back out and left. The atom had now changed its polarity and become entangled with Laura, and in essence, the cavity itself.
Once this system was set up we had to decide what atoms we should entangle. We could not be sure what our atoms may have previously interacted with.
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