From df91fd9f9652057f6450a2b6eddc889534b43b14 Mon Sep 17 00:00:00 2001 From: Mark Date: Thu, 2 Oct 2025 07:56:09 -0700 Subject: [PATCH] Incomplete port --- src/Advanced/Introduction to Quantum/main.typ | 35 ++ .../src/parts/01 bits.typ | 349 ++++++++++++ .../src/parts/02 qubit.typ | 514 ++++++++++++++++++ .../src/parts/03 two qubits.typ | 126 +++++ .../src/parts/04 logic gates.typ | 169 ++++++ .../src/parts/05 quantum gates.typ | 42 ++ .../src/parts/06 hxh.typ | 53 ++ .../src/parts/07 superdense.typ | 48 ++ .../src/parts/08 teleport.typ | 31 ++ 9 files changed, 1367 insertions(+) create mode 100644 src/Advanced/Introduction to Quantum/main.typ create mode 100644 src/Advanced/Introduction to Quantum/src/parts/01 bits.typ create mode 100644 src/Advanced/Introduction to Quantum/src/parts/02 qubit.typ create mode 100644 src/Advanced/Introduction to Quantum/src/parts/03 two qubits.typ create mode 100644 src/Advanced/Introduction to Quantum/src/parts/04 logic gates.typ create mode 100644 src/Advanced/Introduction to Quantum/src/parts/05 quantum gates.typ create mode 100644 src/Advanced/Introduction to Quantum/src/parts/06 hxh.typ create mode 100644 src/Advanced/Introduction to Quantum/src/parts/07 superdense.typ create mode 100644 src/Advanced/Introduction to Quantum/src/parts/08 teleport.typ diff --git a/src/Advanced/Introduction to Quantum/main.typ b/src/Advanced/Introduction to Quantum/main.typ new file mode 100644 index 0000000..2af8fed --- /dev/null +++ b/src/Advanced/Introduction to Quantum/main.typ @@ -0,0 +1,35 @@ +#import "@local/handout:0.1.0": * + +#show: handout.with( + title: [Intro to Quantum Computing], + by: "Mark", +) + +// Define quantum notation macros +#let ket(content) = $|#content angle.r$ +#let bra(content) = $angle.l #content|$ + +#include "src/parts/01 bits.typ" +#pagebreak() + +#include "src/parts/02 qubit.typ" +#pagebreak() + +#include "src/parts/03 two qubits.typ" +#pagebreak() + +// DONE UNTIL HERE + +#include "src/parts/04 logic gates.typ" +#pagebreak() + +#include "src/parts/05 quantum gates.typ" +#pagebreak() + +#include "src/parts/06 hxh.typ" +#pagebreak() + +#include "src/parts/07 superdense.typ" +#pagebreak() + +#include "src/parts/08 teleport.typ" diff --git a/src/Advanced/Introduction to Quantum/src/parts/01 bits.typ b/src/Advanced/Introduction to Quantum/src/parts/01 bits.typ new file mode 100644 index 0000000..7327f1c --- /dev/null +++ b/src/Advanced/Introduction to Quantum/src/parts/01 bits.typ @@ -0,0 +1,349 @@ +#import "@local/handout:0.1.0": * +#import "@preview/cetz:0.4.2" + += Probabilistic Bits + +#definition() +As we already know, a _classical bit_ may take the values `0` and `1`. + +We can model this with a two-sided coin, one face of which is labeled `0`, and the other, `1`. + +#v(2mm) + +Of course, if we toss such a "bit-coin," we'll get either `0` or `1`. + +We'll denote the probability of getting `0` as $p_0$, and the probability of getting `1` as $p_1$. + +As with all probabilities, $p_0 + p_1$ must be equal to 1. + +#v(1fr) + +#definition() +Say we toss a "bit-coin" and don't observe the result. We now have a _probabilistic bit_, with a probability $p_0$ of being `0`, and a probability $p_1$ of being `1`. + +#v(2mm) + +We'll represent this probabilistic bit's _state_ as a vector: $mat(p_0; p_1)$ + +We do *not* assume this coin is fair, and thus $p_0$ might not equal $p_1$. + +#note[This may seem a bit redundant: since $p_0 + p_1 = 1$, we can always calculate one probability given the other. We'll still include both probabilities in the state vector, since this provides a clearer analogy to quantum bits.] + +#v(1fr) + +#definition() +The simplest probabilistic bit states are of course $[0]$ and $[1]$, defined as follows: +- $[0] = mat(1; 0)$ +- $[1] = mat(0; 1)$ + +That is, $[0]$ represents a bit that we known to be `0`, and $[1]$ represents a bit we know to be `1`. + +#v(1fr) + +#definition() +$[0]$ and $[1]$ form a _basis_ for all possible probabilistic bit states: + +Every other probabilistic bit can be written as a _linear combination_ of $[0]$ and $[1]$: + +$ mat(p_0; p_1) = p_0 mat(1; 0) + p_1 mat(0; 1) = p_0 [0] + p_1 [1] $ + +#v(1fr) +#pagebreak() + +#problem() +Every possible state of a probabilistic bit is a two-dimensional vector. + +Draw all possible states on the axis below. + +#table( + columns: (1fr,), + align: center, + stroke: none, + align(center, cetz.canvas({ + import cetz.draw: * + + set-style(content: (frame: "rect", stroke: none, fill: none, padding: .25)) + scale(200%) + + line( + (0, 1.5), + (0, 0), + (1.5, 0), + stroke: black + 0.25mm, + ) + mark((0, 1.5), (0, 2), symbol: ")>", fill: black) + mark((1.5, 0), (2, 0), symbol: ")>", fill: black) + + content((0, 1.5), $p_1$, anchor: "south") + content((1.5, 0), $p_0$, anchor: "west") + + circle((0, 0), radius: 0.6mm, fill: black, name: "00") + content("00.south", $mat(0; 0)$, anchor: "north") + + circle((0, 1), radius: 0.6mm, fill: oblue, stroke: oblue, name: "00") + content("00.west", $[1]$, anchor: "east") + + circle((1, 0), radius: 0.6mm, fill: oblue, stroke: oblue, name: "00") + content("00.south", $[0]$, anchor: "north") + })), +) + +#solution[ + #table( + columns: (1fr,), + align: center, + stroke: none, + align(center, cetz.canvas({ + import cetz.draw: * + + set-style(content: ( + frame: "rect", + stroke: none, + fill: none, + padding: .25, + )) + scale(200%) + + line( + (0, 1.5), + (0, 0), + (1.5, 0), + stroke: black + 0.25mm, + ) + mark((0, 1.5), (0, 2), symbol: ")>", fill: black) + mark((1.5, 0), (2, 0), symbol: ")>", fill: black) + + content((0, 1.5), $p_1$, anchor: "south") + content((1.5, 0), $p_0$, anchor: "west") + + + line( + (1, 0), + (0, 1), + stroke: ored + 1mm, + ) + + circle((0, 0), radius: 0.6mm, fill: black, name: "00") + content("00.south", $mat(0; 0)$, anchor: "north") + + circle((0, 1), radius: 0.6mm, fill: oblue, stroke: oblue, name: "00") + content("00.west", $[1]$, anchor: "east") + + circle((1, 0), radius: 0.6mm, fill: oblue, stroke: oblue, name: "00") + content("00.south", $[0]$, anchor: "north") + })), + ) + +] + + +#v(1fr) +#pagebreak() + += Measuring Probabilistic Bits + +#definition() +As we noted before, a probabilistic bit represents a coin we've tossed but haven't looked at. + +We do not know whether the bit is `0` or `1`, but we do know the probability of both of these outcomes. + +#v(2mm) + +If we _measure_ (or _observe_) a probabilistic bit, we see either `0` or `1`—and thus our knowledge of its state is updated to either $[0]$ or $[1]$, since we now certainly know what face the coin landed on. + +#v(2mm) + +Since measurement changes what we know about a probabilistic bit, it changes the probabilistic bit's state. When we measure a bit, its state _collapses_ to either $[0]$ or $[1]$, and the original state of the bit vanishes. We _cannot_ recover the state $[x_0, x_1]$ from a measured probabilistic bit. + +#definition("Multiple bits") +Say we have two probabilistic bits, $x$ and $y$, with states $[x] = [x_0, x_1]$ and $[y] = [y_0, y_1]$ + +#v(2mm) + +The _compound state_ of $[x]$ and $[y]$ is exactly what it sounds like: It is the probabilistic two-bit state $|x y angle.r$, where the probabilities of the first bit are determined by $[x]$, and the probabilities of the second are determined by $[y]$. + +#problem(label: "firstcompoundstate") +Say $[x] = [2/3, 1/3]$ and $[y] = [3/4, 1/4]$. + +- If we measure $x$ and $y$ simultaneously, what is the probability of getting each of `00`, `01`, `10`, and `11`? + +- If we measure $y$ first and observe `1`, what is the probability of getting each of `00`, `01`, `10`, and `11`? + +#note[*Note:* $[x]$ and $[y]$ are column vectors, but I've written them horizontally to save space.] + +#v(1fr) + +#problem() +Say $[x] = [2/3, 1/3]$ and $[y] = [3/4, 1/4]$. + +What is the probability that $x$ and $y$ produce different outcomes? + +#v(1fr) +#pagebreak() + += Tensor Products + +#definition("Tensor Products") +The _tensor product_ of two vectors is defined as follows: +$ + mat(x_1; x_2) times.circle mat(y_1; y_2) = mat(x_1 mat(y_1; y_2); x_2 mat(y_1; y_2)) = mat(x_1 y_1; x_1 y_2; x_2 y_1; x_2 y_2) +$ + +That is, we take our first vector, multiply the second vector by each of its components, and stack the result. You could think of this as a generalization of scalar multiplication, where scalar multiplication is a tensor product with a vector in $RR^1$: + +$ + a mat(x_1; x_2) = mat(a_1) times.circle mat(y_1; y_2) = mat(a_1 mat(y_1; y_2)) = mat(a_1 y_1; a_1 y_2) +$ + +#problem() +Say $x in RR^n$ and $y in RR^m$. + +What is the dimension of $x times.circle y$? + +#v(1fr) + +#problem(label: "basistp") +What is the following pairwise tensor product? +#v(4mm) +$ + {mat(1; 0; 0), mat(0; 1; 0), mat(0; 0; 1)} + times.circle + {mat(1; 0), mat(0; 1)} +$ +#v(4mm) + +#hint[Distribute the tensor product between every pair of vectors.] + +#v(1fr) + +#problem() +What is the _span_ of the vectors we found in @basistp? + +In other words, what is the set of vectors that can be written as linear combinations of the vectors above? + +#v(1fr) + +#pagebreak() + +#problem() +Say $[x] = [2/3, 1/3]$ and $[y] = [3/4, 1/4]$. + +What is $[x] times.circle [y]$? How does this relate to @firstcompoundstate? + +#v(1fr) + +#problem() +The compound state of two vector-form bits is their tensor product. + +Compute the following. Is the result what we'd expect? +- $[0] times.circle [0]$ +- $[0] times.circle [1]$ +- $[1] times.circle [0]$ +- $[1] times.circle [1]$ + +#hint[Remember that $[0] = mat(1; 0)$ and $[1] = mat(0; 1)$.] + +#v(1fr) + +#problem(label: "fivequant") +Writing $[0] times.circle [1]$ is a bit tedious. We'll shorten this notation to $[01]$. + +In fact, we could go further: if we wanted to write the set of bits $[1] times.circle [1] times.circle [0] times.circle [1]$, \ +we could write $[1101]$—but a shorter alternative is $[13]$, since $13$ is `1101` in binary. + +#v(2mm) + +Write $[5]$ as a three-bit probabilistic state. + +#solution[ + $[5] = [101] = [1] times.circle [0] times.circle [1] = [0,0,0,0,0,1,0,0]^T$ \ + + Notice how we're counting from the top, with $[000] = [1,0,...,0]$ and $[111] = [0, ..., 0, 1]$. +] + +#v(1fr) + +#problem() +Write the three-bit states $[0]$ through $[7]$ as column vectors. + +#hint[You do not need to compute every tensor product. Do a few and find the pattern.] + +#v(1fr) +#pagebreak() + + + += Operations on Probabilistic Bits + +Now that we can write probabilistic bits as vectors, we can represent operations on these bits with linear transformations—in other words, as matrices. + +#definition() +Consider the NOT gate, which operates as follows: +- $"NOT"[0] = [1]$ +- $"NOT"[1] = [0]$ + +What should NOT do to a probabilistic bit $[x_0, x_1]$? + +If we return to our coin analogy, we can think of the NOT operation as flipping a coin we have already tossed, without looking at its state. Thus, +$ "NOT" mat(x_0; x_1) = mat(x_1; x_0) $ + +#review_box("Review: Multiplying vectors by matrices")[ + #v(2mm) + + $ + A v = mat(1, 2; 3, 4) mat(v_0; v_1) = mat(1 v_0 + 2 v_1; 3 v_0 + 4 v_1) + $ + + #v(2mm) + + Note that each element of $A v$ is the dot product of a row in $A$ and a column in $v$. +] + +#problem() +Compute the following product: +$ mat(1, 0.5; 0, 1) mat(3; 2) $ + +#v(1fr) + +#remark() +Also, recall that every matrix is linear map, and that every linear map may be written as a matrix. We often use the terms _matrix_, _transformation_, and _linear map_ interchangeably. + +#pagebreak() + +#problem() +Find the matrix that represents the NOT operation on one probabilistic bit. + +#solution[ + $ + mat(0, 1; 1, 0) + $ +] + +#v(1fr) + +#problem("Extension by linearity") +Say we have an arbitrary operation $M$. + +If we know how $M$ acts on $[1]$ and $[0]$, can we compute $M[x]$ for an arbitrary state $[x]$? + +Say $[x] = [x_0, x_1]$. +- What is the probability we observe $0$ when we measure $x$? +- What is the probability that we observe $M[0]$ when we measure $M x$? + +#v(1fr) + +#problem(label: "linearextension") +Write $M[x_0, x_1]$ in terms of $M[0]$, $M[1]$, $x_0$, and $x_1$. + +#solution[ + $ + M mat(x_0; x_1) = x_0 M mat(1; 0) + x_1 M mat(0; 1) = x_0 M[0] + x_1 M[1] + $ +] + +#v(1fr) + +#remark() Every matrix represents a _linear_ map, so the following is always true: +$ A times (p x + q y) = p A x + q A y $ + +@linearextension is just a special case of this fact. diff --git a/src/Advanced/Introduction to Quantum/src/parts/02 qubit.typ b/src/Advanced/Introduction to Quantum/src/parts/02 qubit.typ new file mode 100644 index 0000000..7ed2559 --- /dev/null +++ b/src/Advanced/Introduction to Quantum/src/parts/02 qubit.typ @@ -0,0 +1,514 @@ +#import "@local/handout:0.1.0": * +#import "@preview/cetz:0.4.2" + +// Define quantum notation macros +#let ket(content) = $|#content angle.r$ +#let bra(content) = $angle.l #content|$ + += One Qubit + +Quantum bits (or _qubits_) are very similar to probabilistic bits, but have one major difference: probabilities are replaced with _amplitudes_. + +#v(2mm) + +Of course, a qubit can take the values `0` and `1`, which are denoted $#ket("0")$ and $#ket("1")$. + +Like probabilistic bits, a quantum bit is written as a linear combination of $#ket("0")$ and $#ket("1")$: +$ #ket([$psi$]) = psi_0 #ket("0") + psi_1 #ket("1") $ + +Such linear combinations are called _superpositions_. + +#v(2mm) + +The $#ket("")$ you see in the expressions above is called a "ket," and denotes a column vector. + +$#ket("0")$ is pronounced "ket zero," and $#ket("1")$ is pronounced "ket one." This is called bra-ket notation. + +#note[*Note:* $#bra("0")$ is called a "bra," but we won't worry about that for now.] + +#v(2mm) + +This is very similar to the "box" $[#h(1.5mm)]$ notation we used for probabilistic bits. + +As before, we will write $#ket("0") = mat(1; 0)$ and $#ket("1") = mat(0; 1)$. + +#v(8mm) + +Recall that probabilistic bits are subject to the restriction that $p_0 + p_1 = 1$. + +Quantum bits have a similar condition: $psi_0^2 + psi_1^2 = 1$. + +Note that this implies that $psi_0$ and $psi_1$ are both in $[-1, 1]$. + +Quantum amplitudes may be negative, but probabilistic bit probabilities cannot. + +#v(2mm) + +If we plot the set of valid quantum states on our plane, we get a unit circle centered at the origin: + +#table( + columns: (1fr,), + align: center, + stroke: none, + align(center, cetz.canvas({ + import cetz.draw: * + + set-style(content: (frame: "rect", stroke: none, fill: none, padding: .25)) + scale(150%) + + line( + (0, 1.5), + (0, 0), + (1.5, 0), + stroke: black + 0.25mm, + ) + mark((0, 1.5), (0, 2), symbol: ")>", fill: black) + mark((1.5, 0), (2, 0), symbol: ")>", fill: black) + + circle((0, 0), radius: 1, stroke: ( + paint: black, + thickness: 0.25mm, + dash: "dashed", + )) + + content((0, 1.5), $p_1$, anchor: "south") + content((1.5, 0), $p_0$, anchor: "west") + + circle((0, 1), radius: 0.6mm, fill: oblue, stroke: oblue, name: "00") + content("00.west", $#ket("1")$, anchor: "east") + + circle((1, 0), radius: 0.6mm, fill: oblue, stroke: oblue, name: "00") + content("00.south", $#ket("0")$, anchor: "north") + + circle((0.87, 0.5), radius: 0.6mm, fill: ored, stroke: ored, name: "00") + content("00.east", $#ket(math.psi)$, anchor: "west") + })), +) + + +Recall that the set of probabilistic bits forms a line instead: + +#table( + columns: (1fr,), + align: center, + stroke: none, + align(center, cetz.canvas({ + import cetz.draw: * + + set-style(content: (frame: "rect", stroke: none, fill: none, padding: .25)) + scale(150%) + + line( + (0, 1.5), + (0, 0), + (1.5, 0), + stroke: black + 0.25mm, + ) + mark((0, 1.5), (0, 2), symbol: ")>", fill: black) + mark((1.5, 0), (2, 0), symbol: ")>", fill: black) + + + line( + (1, 0), + (0, 1), + stroke: ored + 1mm, + ) + + content((0, 1.5), $p_1$, anchor: "south") + content((1.5, 0), $p_0$, anchor: "west") + + circle((0, 0), radius: 0.6mm, fill: black, name: "00") + content("00.south", $mat(0; 0)$, anchor: "north") + + circle((0, 1), radius: 0.6mm, fill: oblue, stroke: oblue, name: "00") + content("00.west", $[1]$, anchor: "east") + + circle((1, 0), radius: 0.6mm, fill: oblue, stroke: oblue, name: "00") + content("00.south", $[0]$, anchor: "north") + })), +) + + +#problem() +In the above unit circle, the counterclockwise angle from $#ket("0")$ to $#ket([$psi$])$ is $30°$. + +Write $#ket([$psi$])$ as a linear combination of $#ket("0")$ and $#ket("1")$. + +#v(1fr) +#pagebreak() + +#definition("Measurement I") +Just like a probabilistic bit, we must observed $#ket("0")$ or $#ket("1")$ when we measure a qubit. + +If we were to measure $#ket([$psi$]) = psi_0 #ket("0") + psi_1 #ket("1")$, we'd observe either $#ket("0")$ or $#ket("1")$, with the following probabilities: +- $cal(P)(#ket("1")) = psi_1^2$ +- $cal(P)(#ket("0")) = psi_0^2$ + +#note[Note that $cal(P)(#ket("0")) + cal(P)(#ket("1")) = 1$.] + +#v(2mm) + +As before, $#ket([$psi$])$ _collapses_ when it is measured: its state becomes that which we observed in our measurement, leaving no trace of the previous superposition. + +#problem() +- What is the probability we observe $#ket("0")$ when we measure $#ket([$psi$])$? +- What can we observe if we measure $#ket([$psi$])$ a second time? +- What are these probabilities for $#ket([$phi$])$? + + +#table( + columns: (1fr,), + align: center, + stroke: none, + align(center, cetz.canvas({ + import cetz.draw: * + + set-style(content: (frame: "rect", stroke: none, fill: none, padding: .25)) + scale(200%) + + line( + (0, 1.5), + (0, 0), + (1.5, 0), + stroke: black + 0.25mm, + ) + mark((0, 1.5), (0, 2), symbol: ")>", fill: black) + mark((1.5, 0), (2, 0), symbol: ")>", fill: black) + + circle((0, 0), radius: 1, stroke: ( + paint: black, + thickness: 0.25mm, + dash: "dashed", + )) + + content((0, 1.5), $p_1$, anchor: "south") + content((1.5, 0), $p_0$, anchor: "west") + + circle((0, 1), radius: 0.6mm, fill: oblue, stroke: oblue, name: "00") + content("00.west", $#ket("1")$, anchor: "east") + + circle((1, 0), radius: 0.6mm, fill: oblue, stroke: oblue, name: "00") + content("00.south", $#ket("0")$, anchor: "north") + + circle((0.87, 0.5), radius: 0.6mm, fill: ored, stroke: ored, name: "00") + content("00.east", $#ket(math.psi)$, anchor: "west") + + arc( + (0, 0), + start: 0deg, + stop: -135deg, + anchor: "origin", + radius: 0.3, + name: "a135", + stroke: gray, + ) + mark( + "a135.end", + 135deg, + symbol: ")>", + fill: gray, + stroke: gray, + ) + content("a135.center", text(fill: gray)[$135degree$], anchor: "north") + + + line((0, 0), (-0.607, -0.607), stroke: ( + paint: gray, + thickness: 0.4mm, + dash: "dotted", + )) + mark( + (-0.627, -0.627), + (-0.708, -0.708), + symbol: ")>", + fill: gray, + stroke: gray, + ) + + + arc( + (0, 0), + start: 0deg, + stop: 30deg, + anchor: "origin", + radius: 0.6, + name: "a30", + stroke: gray, + ) + mark( + "a30.end", + 120deg, + symbol: ")>", + fill: gray, + stroke: gray, + ) + content("a30.end", text(fill: gray)[$30degree$], anchor: "south") + + + line((0, 0), (0.87, 0.5), stroke: ( + paint: gray, + thickness: 0.4mm, + dash: "dotted", + )) + mark( + (0.80, 0.46), + (0.87, 0.5), + symbol: ")>", + fill: gray, + stroke: gray, + ) + + circle( + (-0.707, -0.707), + radius: 0.6mm, + fill: ored, + stroke: ored, + name: "00", + ) + content("00.west", $#ket(math.phi)$, anchor: "east") + })), +) + + + +#v(1fr) + +As you may have noticed, we don't need two coordinates to fully define a qubit's state. We can get by with one coordinate just as well. + +Instead of referring to each state using its cartesian coordinates $psi_0$ and $psi_1$, we can address it using its _polar angle_ $theta$, measured from $#ket("0")$ counterclockwise: + +#table( + columns: (1fr,), + align: center, + stroke: none, + align(center, cetz.canvas({ + import cetz.draw: * + + set-style(content: (frame: "rect", stroke: none, fill: none, padding: .25)) + scale(180%) + + line( + (0, 1.5), + (0, 0), + (1.5, 0), + stroke: black + 0.25mm, + ) + mark((0, 1.5), (0, 2), symbol: ")>", fill: black) + mark((1.5, 0), (2, 0), symbol: ")>", fill: black) + + circle((0, 0), radius: 1, stroke: ( + paint: black, + thickness: 0.25mm, + dash: "dashed", + )) + + content((0, 1.5), $p_1$, anchor: "south") + content((1.5, 0), $p_0$, anchor: "west") + + circle((0, 1), radius: 0.6mm, fill: oblue, stroke: oblue, name: "00") + content("00.west", $#ket("1")$, anchor: "east") + + circle((1, 0), radius: 0.6mm, fill: oblue, stroke: oblue, name: "00") + content("00.south", $#ket("0")$, anchor: "north") + + circle((0.87, 0.5), radius: 0.6mm, fill: ored, stroke: ored, name: "00") + content("00.east", $#ket(math.psi)$, anchor: "west") + + + arc( + (0, 0), + start: 0deg, + stop: 30deg, + anchor: "origin", + radius: 0.6, + name: "a30", + stroke: gray, + ) + mark( + "a30.end", + 120deg, + symbol: ")>", + fill: gray, + stroke: gray, + ) + content("a30.mid", text(fill: gray)[$theta$], anchor: "west") + + + line((0, 0), (0.87, 0.5), stroke: ( + paint: gray, + thickness: 0.4mm, + dash: "dotted", + )) + mark( + (0.80, 0.46), + (0.87, 0.5), + symbol: ")>", + fill: gray, + stroke: gray, + ) + })), +) + + +#problem() +Find $psi_0$ and $psi_1$ in terms of $theta$ for an arbitrary qubit $psi$. + +#v(1fr) +#pagebreak() + +#problem() +Consider the following qubit states: + +#grid( + columns: (1fr, 1fr), + $ #ket("+") = (#ket("0") + #ket("1"))/sqrt(2) $, + $ #ket("-") = (#ket("0") - #ket("1"))/sqrt(2) $, +) + +- Where are these on the unit circle? +- What are their polar angles? +- What are the probabilities of observing $#ket("0")$ and $#ket("1")$ when measuring $#ket("+")$ and $#ket("-")$? + + + +#table( + columns: (1fr,), + align: center, + stroke: none, + align(center, cetz.canvas({ + import cetz.draw: * + + set-style(content: (frame: "rect", stroke: none, fill: none, padding: .25)) + scale(300%) + + line( + (0, 1.3), + (0, 0), + (1.3, 0), + stroke: black + 0.25mm, + ) + mark((0, 1.3), (0, 2), symbol: ")>", fill: black) + mark((1.3, 0), (2, 0), symbol: ")>", fill: black) + + circle((0, 0), radius: 1, stroke: ( + paint: black, + thickness: 0.25mm, + dash: "dashed", + )) + + content((0, 1.3), $p_1$, anchor: "south") + content((1.3, 0), $p_0$, anchor: "west") + + circle((0, 1), radius: 0.4mm, fill: oblue, stroke: oblue, name: "00") + content("00.west", $#ket("1")$, anchor: "east") + + circle((1, 0), radius: 0.4mm, fill: oblue, stroke: oblue, name: "00") + content("00.south", $#ket("0")$, anchor: "north") + })), +) + + +#v(1fr) + +#v(1fr) +#v(1fr) +#pagebreak() + += Operations on One Qubit + +We may apply transformations to qubits just as we apply transformations to probabilistic bits. Again, we'll represent transformations as $2 times 2$ matrices, since we want to map one qubit state to another. + +#note[In other words, we want to map elements of $RR^2$ to elements of $RR^2$.] + +We will call such maps _quantum gates,_ since they are the quantum equivalent of classical logic gates. + +#v(2mm) + +There are two conditions a valid quantum gate $G$ must satisfy: +- For any valid state $#ket([$psi$])$, $G #ket([$psi$])$ is a valid state. Namely, $G$ must preserve the length of any vector it is applied to. Recall that the set of valid quantum states is the set of unit vectors in $RR^2$ + +- Any quantum gate must be _invertible_. We'll skip this condition for now, and return to it later. + +In short, a quantum gate is a linear map that maps the unit circle to itself. There are only two kinds of linear maps that do this: reflections and rotations. + +#problem() +The $X$ gate is the quantum analog of the `not` gate, defined by the following table: +- $X #ket("0") = #ket("1")$ +- $X #ket("1") = #ket("0")$ + +Find the matrix $X$. + +#solution[ + $ + mat(0, 1; 1, 0) + $ +] + +#v(1fr) + +#problem() +What is $X #ket("+")$ and $X #ket("-")$? + +#hint[Remember that all matrices are linear maps. What does this mean?] + +#solution[ + $X #ket("+") = #ket("+")$ and $X #ket("-") = - #ket("-")$ (that is, a negative ket-minus). \ + Most notably, rememver that $G(a#ket("0") + b #ket("1")) = a G #ket("0") + b G #ket("1")$. +] + +#v(1fr) + +#problem() +In terms of geometric transformations, what does $X$ do to the unit circle? + +#solution[ + It is a reflection about the $45degree$ axis. +] + +#v(1fr) +#pagebreak() + +#problem() +Let $Z$ be a quantum gate defined by the following table: +- $Z #ket("0") = #ket("0")$, +- $Z #ket("1") = -#ket("1")$. + +What is the matrix $Z$? What are $Z #ket("+")$ and $Z #ket("-")$? + +What is $Z$ as a geometric transformation? + +#v(1fr) + +#problem() +Is the map $B$ defined by the table below a valid quantum gate? +- $B #ket("0") = #ket("0")$ +- $B #ket("1") = #ket("+")$ + +#hint[Find a $#ket([$psi$])$ so that $B #ket([$psi$])$ is not a valid qubit state] + +#solution[ + $ B #ket("+") = (1 + sqrt(2))/(2) #ket("0") + 1/2 #ket("1") $ + + This has a non-unit length of + $ + (sqrt(2) + 1)/(2) + $ +] + +#v(1fr) + +#problem("Rotation") +As we noted earlier, any rotation about the center is a valid quantum gate. Let's derive all transformations of this form. + +- Let $U_theta$ be the matrix that represents a counterclockwise rotation of $theta$ degrees. What is $U #ket("0")$ and $U #ket("1")$? + +- Find the matrix $U_theta$ for an arbitrary $theta$. + +#v(1fr) + +#problem() +Say we have a qubit that is either $#ket("+")$ or $#ket("-")$. We do not know which of the two states it is in. + +Using one operation and one measurement, how can we find out, for certain, which qubit we received? + +#v(1fr) diff --git a/src/Advanced/Introduction to Quantum/src/parts/03 two qubits.typ b/src/Advanced/Introduction to Quantum/src/parts/03 two qubits.typ new file mode 100644 index 0000000..3e1a70d --- /dev/null +++ b/src/Advanced/Introduction to Quantum/src/parts/03 two qubits.typ @@ -0,0 +1,126 @@ +#import "@local/handout:0.1.0": * + +// Define quantum notation macros +#let ket(content) = $|#content angle.r$ +#let bra(content) = $angle.l #content|$ + += Two Qubits + +#definition() +Just as before, we'll represent multi-qubit states as linear combinations of multi-qubit basis states. + +For example, a two-qubit state $#ket("ab")$ is the four-dimensional unit vector +$ mat(a; b; c; d) = a #ket("00") + b #ket("01") + c #ket("10") + d #ket("11") $ + +As always, multi-qubit states are unit vectors. Thus, $a^2 + b^2 + c^2 + d^2 = 1$ in the two-bit case above. + +#problem() +Say we have two qubits $#ket([$psi$])$ and $#ket([$phi$])$. + +Show that $#ket([$psi$]) times.circle #ket([$phi$])$ is always a unit vector (and is thus a valid quantum state). + +#v(1fr) + +#definition("Measurement II") +Measurement of a two-qubit state works just like measurement of a one-qubit state: + +If we measure $a #ket("00") + b #ket("01") + c #ket("10") + d #ket("11")$, we get one of the four basis states with the following probabilities: + +- $cal(P)(#ket("00")) = a^2$ +- $cal(P)(#ket("01")) = b^2$ +- $cal(P)(#ket("10")) = c^2$ +- $cal(P)(#ket("11")) = d^2$ + +As before, the sum of all the above probabilities is $1$. + +#problem() +Consider the two-qubit state +$#ket([$psi$]) = 1/sqrt(2) #ket("00") + 1/2 #ket("01") + sqrt(3)/4 #ket("10") + 1/4 #ket("11")$ + +- If we measure both bits of $#ket([$psi$])$ simultaneously, what is the probability of getting each of $#ket("00")$, $#ket("01")$, $#ket("10")$, and $#ket("11")$? + +- If we measure the ONLY the first qubit, what is the probability we get $#ket("0")$? How about $#ket("1")$? + + #hint[There are two basis states in which the first qubit is $#ket("0")$.] + +- Say we measured the second bit and read $#ket("1")$. If we now measure the first bit, what is the probability of getting $#ket("0")$? + +#v(1fr) +#pagebreak() + +#problem() +Again, consider the two-qubit state +$#ket([$psi$]) = 1/sqrt(2) #ket("00") + 1/2 #ket("01") + sqrt(3)/4 #ket("10") + 1/4 #ket("11")$ + +If we measure the first qubit of $#ket([$psi$])$ and get $#ket("0")$, what is the resulting state of $#ket([$psi$])$? + +What would the state be if we'd measured $#ket("1")$ instead? + +#v(1fr) + +#problem() +Consider the three-qubit state $#ket([$psi$]) = c_0 #ket("000") + c_1 #ket("001") + ... + c_7 #ket("111")$. + +Say we measure the first two qubits and get $#ket("00")$. What is the resulting state of $#ket([$psi$])$? + +#solution[ + We measure $#ket("00")$ with probability $c_0^2 + c_1^2$, and $#ket(math.psi)$ collapses to + + #v(3mm) + + $ + (c_0 #ket("000") + c_1 #ket("001"))/(sqrt(c_0^2 + c_1^2)) + $ +] + + +#v(1fr) +#pagebreak() + +#definition("Entanglement") +Some product states can be factored into a tensor product of individual qubit states. For example, +$ + 1/2 (#ket("00") + #ket("01") + #ket("10") + #ket("11")) = 1/sqrt(2) (#ket("0") + #ket("1")) times.circle 1/sqrt(2) (#ket("0") + #ket("1")) +$ + +Such states are called _product states._ States that aren't product states are called _entangled_ states. + +#problem() +Factor the following product state: +$ + 1/(2sqrt(2)) (sqrt(3) #ket("00") - sqrt(3) #ket("01") + #ket("10") - #ket("11")) +$ + +#solution[ + + $ + (1)/(2 sqrt(2)) (sqrt(3) #ket("00") - sqrt(3) #ket("01") + #ket("10") - #ket("11")) + = (sqrt(3)/2 #ket("0") + 1/2 #ket("1") ) + times.circle + ( 1/sqrt(2) #ket(0) - 1/sqrt(2) #ket("1")) + $ +] + +#v(1fr) + +#problem() +Show that the following is an entangled state. +$ 1/sqrt(2) #ket("00") + 1/sqrt(2) #ket("11") $ + +#solution[ + $ + mat(a_0; a_1) + times.circle + mat(b_0; b_1) + = + a_0b_0 #ket(00) + a_0b_1 #ket(01) + a_1b_0 #ket(10) + a_1b_1 #ket(11) + $ + + #v(2mm) + + So, we have that $a_1b_1 = a_0b_0 = sqrt(2)^(-1)$ \ + But $a_0b_1 = a_1b_0 = 0$, so one of $a_0$ and $b_1$ must be zero. \ + We thus have a contradiction. +] + +#v(1fr) diff --git a/src/Advanced/Introduction to Quantum/src/parts/04 logic gates.typ b/src/Advanced/Introduction to Quantum/src/parts/04 logic gates.typ new file mode 100644 index 0000000..15d1ccd --- /dev/null +++ b/src/Advanced/Introduction to Quantum/src/parts/04 logic gates.typ @@ -0,0 +1,169 @@ +#import "@local/handout:0.1.0": * + +// Define quantum notation macros +#let ket(content) = $|#content angle.r$ +#let bra(content) = $angle.l #content|$ + += Logic Gates + +#definition("Matrices") +Throughout this handout, we've been using matrices. Again, recall that every linear map may be written as a matrix, and that every matrix represents a linear map. For example, if $f: RR^2 -> RR^2$ is a linear map, we can write it as follows: + +$ + f(#ket("x")) = mat(m_1, m_2; m_3, m_4) mat(x_1; x_2) = mat(m_1 x_1 + m_2 x_2; m_3 x_1 + m_4 x_2) +$ + +#definition() +Before we discussing multi-qubit quantum gates, we need to review to classical logic. + +Of course, a classical logic gate is a linear map from ${0,1}^m$ to ${0,1}^n$ + +#problem() +The `not` gate is a map defined by the following table: + +- $X #ket("0") = #ket("1")$ +- $X #ket("1") = #ket("0")$ + +Write the `not` gate as a matrix that operates on single-bit vector states. + +That is, find a matrix $X$ so that $X mat(1; 0) = mat(0; 1)$ and $X mat(0; 1) = mat(1; 0)$ + +#solution[ + $ + X = mat(0, 1; 1, 0) + $ +] + +#v(1fr) + +#problem() +The `and` gate is a map $BB^2 -> BB$ defined by the following table: + +#align(center, table( + columns: 3, + stroke: none, + table.hline(), + [`a`], [`b`], [`a` and `b`], + table.hline(), + [0], [0], [0], + [0], [1], [0], + [1], [0], [0], + [1], [1], [1], + table.hline(), +)) + +Find a matrix $A$ so that $A #ket("ab")$ works as expected. + +#hint[Remember, we write bits as vectors.] + +#solution[ + $ + A = mat(1, 1, 1, 0; 0, 0, 0, 1) + $ + + #instructornote[ + Because of the way we represent bits here, we also have the following property: \ + The columns of $A$ correspond to the output for each input---i.e, $A$ is just a table of outputs. \ + + #v(2mm) + + For example, if we look at the first column of $A$ (which is $[1, 0]$), we see: \ + $A#ket(00) = A[1,0,0,0] = [1,0] = #ket(0)$ + + #v(2mm) + + Also with the last column (which is $[0,1]$): \ + $A#ket(00) = A[0,0,0,1] = [0,1] = #ket(1)$ + ] +] + +#v(1fr) +#pagebreak() + +#remark() +The way a quantum circuit handles information is a bit different than the way a classical circuit does. We usually think of logic gates as _functions_: they consume one set of bits, and return another/ + +// TODO: and gate (input a, input b, output) + +#v(2mm) + +This model, however, won't work for quantum logic. If we want to understand quantum gates, we need to see them not as _functions_, but as _transformations_. This distinction is subtle, but significant: +- functions _consume_ a set of inputs and _produce_ a set of outputs +- transformations _change_ a set of objects, without adding or removing any elements + +#v(2mm) + +Our usual logic circuit notation models logic gates as functions—we thus can't use it. We'll need a different diagram to draw quantum circuits. + +#v(1fr) + +First, we'll need a set of bits. For this example, we'll use two, drawn in a vertical array. We'll also add a horizontal time axis, moving from left to right: + +#align(center)[ + // Quantum circuit diagram showing two qubits over time + #box(width: 10cm, height: 4cm)[ + _[Quantum circuit diagram with time axis would go here]_ + ] +] + +In the diagram above, we didn't change our bits—so the labels at the start match those at the end. + +#v(1fr) + +Thus, our circuit forms a grid, with bits ordered vertically and time horizontally. If we want to change our state, we draw transformations as vertical boxes. Every column represents a single transformation on the entire state: + +#align(center)[ + // Quantum circuit with transformations + #box(width: 10cm, height: 4cm)[ + _[Quantum circuit with transformations $T_1$, $T_2$, $T_3$ would go here]_ + ] +] + +Note that the transformations above span the whole state. This is important: we cannot apply transformations to individual bits—we always transform the _entire_ state. + +#v(1fr) +#pagebreak() + +*Setup:* Say we want to invert the first bit of a two-bit state. That is, we want a transformation $T$ so that + +#align(center)[ + // Circuit showing bit flip + #box(width: 8cm, height: 3cm)[ + _[Circuit diagram showing first bit flip would go here]_ + ] +] + +In other words, we want a matrix $T$ satisfying the following equalities: +- $T #ket("00") = #ket("10")$ +- $T #ket("01") = #ket("11")$ +- $T #ket("10") = #ket("00")$ +- $T #ket("11") = #ket("01")$ + +#problem() +Find the matrix that corresponds to the above transformation. + +#hint[Remember that $#ket("0") = mat(1; 0)$ and $#ket("1") = mat(0; 1)$. Also, we found earlier that $X = mat(0, 1; 1, 0)$, and of course $I = mat(1, 0; 0, 1)$.] + +#v(1fr) + +*Remark:* We could draw the above transformation as a combination $X$ and $I$ (identity) gate: + +#align(center)[ + // Circuit with X and I gates + #box(width: 6cm, height: 3cm)[ + _[Circuit diagram with X gate on first qubit, I gate on second would go here]_ + ] +] + +We can even omit the $I$ gate, since we now know that transformations affect the whole state: + +#align(center)[ + // Simplified circuit with just X gate + #box(width: 6cm, height: 3cm)[ + _[Simplified circuit diagram with just X gate on first qubit would go here]_ + ] +] + +We're now done: this is how we draw quantum circuits. Don't forget that transformations _always_ affect the whole state—even if our diagram doesn't explicitly state this. + +#pagebreak() diff --git a/src/Advanced/Introduction to Quantum/src/parts/05 quantum gates.typ b/src/Advanced/Introduction to Quantum/src/parts/05 quantum gates.typ new file mode 100644 index 0000000..33abbc8 --- /dev/null +++ b/src/Advanced/Introduction to Quantum/src/parts/05 quantum gates.typ @@ -0,0 +1,42 @@ +#import "@local/handout:0.1.0": * + +// Define quantum notation macros +#let ket(content) = $|#content angle.r$ +#let bra(content) = $angle.l #content|$ + += Quantum Gates + +In the previous section, we stated that a quantum gate is a linear map. Let's complete that definition. + +#definition() +A quantum gate is a _orthonormal matrix_, which means any gate $G$ satisfies $G G^T = I$. + +This implies the following: + +- $G$ is square. In other words, it has as many rows as it has columns. + + #note[If we think of $G$ as a map, this means that $G$ has as many inputs as it has outputs. This is to be expected: we stated earlier that quantum gates do not destroy or create qubits.] + +- $G$ preserves lengths; i.e $|x| = |G x|$. + + #note[This ensures that $G #ket([$psi$])$ is always a valid state.] + +(You will prove all these properties in any introductory linear algebra course. This isn't a lesson on linear algebra, so you may take them as given today.) + +*Remark:* Let $G$ be a quantum gate. Since quantum gates are, by definition, _linear_ maps, the following holds: + +$ G(a_0 #ket("0") + a_1 #ket("1")) = a_0 G #ket("0") + a_1 G #ket("1") $ + +#problem() +Consider the _controlled not_ (or _cnot_) gate, defined by the following table: +- $X_c #ket("00") = #ket("00")$ +- $X_c #ket("01") = #ket("01")$ +- $X_c #ket("10") = #ket("11")$ +- $X_c #ket("11") = #ket("10")$ + +In other words, the cnot gate inverts its second bit if its first bit is $#ket("1")$. + +Find the matrix that applies the cnot gate. + +#v(1fr) +#pagebreak() diff --git a/src/Advanced/Introduction to Quantum/src/parts/06 hxh.typ b/src/Advanced/Introduction to Quantum/src/parts/06 hxh.typ new file mode 100644 index 0000000..d352c65 --- /dev/null +++ b/src/Advanced/Introduction to Quantum/src/parts/06 hxh.typ @@ -0,0 +1,53 @@ +#import "@local/handout:0.1.0": * + +// Define quantum notation macros +#let ket(content) = $|#content angle.r$ +#let bra(content) = $angle.l #content|$ + += HXH + +Let's return to the quantum circuit diagrams we discussed a few pages ago. Keep in mind that we're working with quantum gates and proper qubits—not classical bits, as we were before. + +#definition("Controlled Inputs") +A _control input_ or _inverted control input_ may be attached to any gate. These are drawn as filled and empty circles in our circuit diagrams: + +#align(center)[ +#grid(columns: (1fr, 1fr), +[ + // Non-inverted control circuit diagram would go here + #box(width: 6cm, height: 4cm)[ + _[Non-inverted control input circuit would go here]_ + ] +], +[ + // Inverted control circuit diagram would go here + #box(width: 6cm, height: 4cm)[ + _[Inverted control input circuit would go here]_ + ] +] +)] + +#v(2mm) + +An $X$ gate with a (non-inverted) control input behaves like an $X$ gate if _all_ its control inputs are $#ket("1")$, and like $I$ otherwise. An $X$ gate with an inverted control inputs does the opposite, behaving like $I$ if its input is $#ket("1")$ and like $X$ otherwise. The two circuits above illustrate this fact—take a look at their inputs and outputs. + +#v(2mm) + +Of course, we can give a gate multiple controls. An $X$ gate with multiple controls behaves like an $X$ gate if... +- all non-inverted controls are $#ket("1")$, and +- all inverted controls are $#ket("0")$ + +...and like $I$ otherwise. + +#problem() +What are the final states of the qubits in the diagram below? + +#align(center)[ + // Multi-control circuit diagram would go here + #box(width: 8cm, height: 6cm)[ + _[Multi-control circuit diagram would go here]_ + ] +] + +#v(1fr) +#pagebreak() \ No newline at end of file diff --git a/src/Advanced/Introduction to Quantum/src/parts/07 superdense.typ b/src/Advanced/Introduction to Quantum/src/parts/07 superdense.typ new file mode 100644 index 0000000..e0bf356 --- /dev/null +++ b/src/Advanced/Introduction to Quantum/src/parts/07 superdense.typ @@ -0,0 +1,48 @@ +#import "@local/handout:0.1.0": * + +// Define quantum notation macros +#let ket(content) = $|#content angle.r$ +#let bra(content) = $angle.l #content|$ + += Superdense Coding + +Consider the following entangled two-qubit states, called the _bell states_: +- $#ket([$Phi^+$]) = 1/sqrt(2) #ket("00") + 1/sqrt(2) #ket("11")$ +- $#ket([$Phi^-$]) = 1/sqrt(2) #ket("00") - 1/sqrt(2) #ket("11")$ +- $#ket([$Psi^+$]) = 1/sqrt(2) #ket("01") + 1/sqrt(2) #ket("10")$ +- $#ket([$Psi^-$]) = 1/sqrt(2) #ket("01") - 1/sqrt(2) #ket("10")$ + +#problem() +The probabilistic bits we get when measuring any of the above may be called _anticorrelated bits_. + +If we measure the first bit of any of these states and observe $1$, what is the resulting compound state? + +What if we observe $0$ instead? + +Do you see why we can call these bits anticorrelated? + +#v(1fr) + +#problem() +Show that the bell states are orthogonal + +#hint[Dot product] + +#v(1fr) + +#problem() +Say we have a pair of qubits in one of the four bell states. + +How can we find out which of the four states we have, with certainty? + +#hint[$H #ket("+") = #ket("0")$, and $H #ket("-") = #ket("1")$] + +#v(1fr) +#pagebreak() + +#definition() +The $Z$ gate is defined as follows: +$ Z mat(psi_0; psi_1) = mat(psi_0; -psi_1) $ + +#v(1fr) +#pagebreak() diff --git a/src/Advanced/Introduction to Quantum/src/parts/08 teleport.typ b/src/Advanced/Introduction to Quantum/src/parts/08 teleport.typ new file mode 100644 index 0000000..a3b86e7 --- /dev/null +++ b/src/Advanced/Introduction to Quantum/src/parts/08 teleport.typ @@ -0,0 +1,31 @@ +#import "@local/handout:0.1.0": * + +// Define quantum notation macros +#let ket(content) = $|#content angle.r$ +#let bra(content) = $angle.l #content|$ + += Quantum Teleportation + +Superdense coding lets us convert quantum bandwidth into classical bandwidth. Quantum teleportation does the opposite, using two classical bits and an entangled pair to transmit a quantum state. + +*Setup:* Again, suppose Alice and Bob each have half of a $#ket([$Phi^+$])$ state. We'll call the state Alice wants to teleport $#ket(math.psi) = psi_0 #ket("0") + psi_1 #ket("1")$. + +#problem() +What is the three-qubit state $#ket(math.psi) #ket([$Phi^+$])$ in terms of $psi_0$ and $psi_1$? + +#v(1fr) + +#problem() +To teleport $#ket(math.psi)$, Alice applies the following circuit to her two qubits, where $#ket([$Phi^+_"A"$])$ is her half of $#ket([$Phi^+$])$. She then measures both qubits and sends the result to Bob. + +#align(center)[ + // Teleportation circuit diagram would go here + #box(width: 8cm, height: 4cm)[ + _[Quantum teleportation circuit diagram would go here]_ + ] +] + +What should Bob do so that $#ket([$Phi^+_"B"$])$ takes the state $#ket(math.psi)$ had initially? + +#v(1fr) +#pagebreak()