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Sensitivity of Various Qubit Detection Methods in Pr:Y2SiO5

Kornienko, Vassily LU (2017) FYSK02 20171
Department of Physics
Atomic Physics
Abstract
The long coherence times of the 4f hyperfine levels of rare-earth-ions gives the possibility to use these as quantum computation devices. Moreover after being doped into a crystal the strong dipole-dipole interaction can be utilized to entangle them. Much work has been done here in Lund to attain as many of the DiVincenzo criteria as possible. At the moment work is being done in the creation of a multiple qubit gate, namely the controlled NOT gate. However, due to an exponential decay in the probability of attaining this gate with respect to the number of involved qubits, along with the low doping concentration, the number of atoms that take part in these gates will be very small. Detecting the signal from such a small population is... (More)
The long coherence times of the 4f hyperfine levels of rare-earth-ions gives the possibility to use these as quantum computation devices. Moreover after being doped into a crystal the strong dipole-dipole interaction can be utilized to entangle them. Much work has been done here in Lund to attain as many of the DiVincenzo criteria as possible. At the moment work is being done in the creation of a multiple qubit gate, namely the controlled NOT gate. However, due to an exponential decay in the probability of attaining this gate with respect to the number of involved qubits, along with the low doping concentration, the number of atoms that take part in these gates will be very small. Detecting the signal from such a small population is problematic. This thesis addresses this problem by comparing the established readout method that consists of a simple scan, with two new readout methods: a slow scan, i.e., a scan with low frequency chirp and a method called superposition beating which incorporates the fundamentals of heterodyne detection with the free induction decay of an ensemble of atoms. A way of calculating the signal to background ratio in order to maximize the existing signal is also proposed and investigated. The results are then compared to Bloch simulations to give a more intuitive grasp of the quantities that are being discussed.
Using the superposition beating method $7$\% of the maximum qubit population could be detected. Furthermore a population resolution of $2$ percentage points was achieved. (Less)
Popular Abstract
Imagine a room where there is one door where you can enter and two doors where you can exit. In each room there is a set of instructions related to if you feel hot or cold. If you feel hot you might have to go through the left door while if you feel cold you might have to go through the right door. There can also be rooms where there is a fireplace, so if you are hot you will just get hotter while if you are cold you warm up. The opposite could be achieved by installing an air conditioner. Now imagine another set of rooms where two people can enter and there are three door where one can exit. The instructions could look like this:

1. If you are both hot one of you should go through the leftmost door.
2. If you are both cold one of you... (More)
Imagine a room where there is one door where you can enter and two doors where you can exit. In each room there is a set of instructions related to if you feel hot or cold. If you feel hot you might have to go through the left door while if you feel cold you might have to go through the right door. There can also be rooms where there is a fireplace, so if you are hot you will just get hotter while if you are cold you warm up. The opposite could be achieved by installing an air conditioner. Now imagine another set of rooms where two people can enter and there are three door where one can exit. The instructions could look like this:

1. If you are both hot one of you should go through the leftmost door.
2. If you are both cold one of you should go through the rightmost door.
3. If one of you is hot and the other one is cold the hot person should go through the middle door.

By interchanging hot and cold with a $1$ and a $0$, the above thought experiment is in direct analogy with a normal computer. The people that are in this maze of rooms are the so-called bits (of which eight make up a byte), and the instructions in every room are put there by the programmers.

If we stay along the lines of this thought experiment, what if one could use the broader sense of hot and cold that humans can feel. For example you could be freezing, cold hands but warm body, both hot and cold because you have contracted a fever or just on the verge of breaking a sweat. This is what the next generation of computers, called quantum computers, will be able to do. These computers will be able to use and control the infinite amount of data that is stored in nature itself without ever having to access it. Many new strange phenomena can also be accessed such as a process called entanglement. This will allow the programmers to control each person in the maze by only controlling one of them. The great science fiction dream of teleportation is also a possibility in this new maze. Everything sounds promising so far, the catch is that that in order for the programmers to be able to use all these new tools, the maze has to be very well isolated from the outside world. The way to solve this is to put it in a building made out of thick slabs of lead.

This isolated building does not seem too bad as long as the set of instructions is put in before the people start walking through the maze. When everybody comes out of the other end, the sequence of hots and colds that they represent will be the answer to what the programmers asked, however there is a thick slab of lead between the two. How does the programmer access the answer? This is the problem that this bachelor thesis addresses.

The type of maze or quantum computer hardware that Lund is investigating uses laser light to give the instructions to atoms that are stuck inside a larger structure, a crystal. Since the number of atoms in this crystal is very low the signals that come from them will be very faint. In the maze analogy the low number of atoms protected by the crystal corresponds to the slab of lead. Hence a new way of reading these signals in a reliable manner has been proposed and investigated in this thesis. (Less)
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author
Kornienko, Vassily LU
supervisor
organization
course
FYSK02 20171
year
type
M2 - Bachelor Degree
subject
keywords
Rare-earth ion quantum computing, Pr:Y2SiO5
language
English
id
8914229
date added to LUP
2017-06-29 20:54:32
date last changed
2017-06-29 20:54:32
@misc{8914229,
  abstract     = {The long coherence times of the 4f hyperfine levels of rare-earth-ions gives the possibility to use these as quantum computation devices. Moreover after being doped into a crystal the strong dipole-dipole interaction can be utilized to entangle them. Much work has been done here in Lund to attain as many of the DiVincenzo criteria as possible. At the moment work is being done in the creation of a multiple qubit gate, namely the controlled NOT gate. However, due to an exponential decay in the probability of attaining this gate with respect to the number of involved qubits, along with the low doping concentration, the number of atoms that take part in these gates will be very small. Detecting the signal from such a small population is problematic. This thesis addresses this problem by comparing the established readout method that consists of a simple scan, with two new readout methods: a slow scan, i.e., a scan with low frequency chirp and a method called superposition beating which incorporates the fundamentals of heterodyne detection with the free induction decay of an ensemble of atoms. A way of calculating the signal to background ratio in order to maximize the existing signal is also proposed and investigated. The results are then compared to Bloch simulations to give a more intuitive grasp of the quantities that are being discussed. 
Using the superposition beating method $7$\% of the maximum qubit population could be detected. Furthermore a population resolution of $2$ percentage points was achieved.},
  author       = {Kornienko, Vassily},
  keyword      = {Rare-earth ion quantum computing,Pr:Y2SiO5},
  language     = {eng},
  note         = {Student Paper},
  title        = {Sensitivity of Various Qubit Detection Methods in Pr:Y2SiO5},
  year         = {2017},
}