Add examples and clean up some stuff

2024-12-08 22:06:58 -08:00
parent 5adc755be4
commit 9b8584bd6f
10 changed files with 275 additions and 102 deletions
@@ -0,0 +1,38 @@
+;;;; An example of Grover's algorithm (quantum search)
+(in-package :cl-quantum/examples)
+
+(defun count-grover-iterations (bits targets)
+  "Count the number of iterations it takes to have a high probability of finding
+TARGETS in a search space of 2^BITS."
+  (values (floor (* (/ pi 4) (sqrt (/ (ash 1 bits) targets))))))
+
+(defun make-grover-circuit (bits target)
+  "Generate a quantum circuit that runs Grover's algorithm over a state of BITS
+bits and finds when the state is equal to TARGET."
+  (assert (> (ash 1 bits) target)
+          (bits target)
+          "Target bit of ~s out of range for state with ~s bits." target bits)
+  (with-build-circuit
+    ;; Setup
+    (loop for i below bits do (:h i))
+
+    ;; Oracle
+    (loop
+      repeat (count-grover-iterations bits 1)
+      do
+         (loop for i below bits
+               for cur = (logand (ash target (- i)) 1)
+               when (zerop cur)
+                 do (:x i))
+         (:ncz 0 (loop for i from 1 below bits collect i))
+         (loop for i below bits
+               for cur = (logand (ash target (- i)) 1)
+               when (zerop cur)
+                 do (:x i))
+
+         ;; Diffuser
+         (loop for i below bits do (:h i))
+         (loop for i below bits do (:x i))
+         (:ncz 0 (loop for i from 1 below bits collect i))
+         (loop for i below bits do (:x i))
+         (loop for i below bits do (:h i)))))