update tutorials (#623)

* refactor [examples] - teleportation

* refactor [examples] - teleportation

remove default optional parameters

Co-authored-by: Theodor <theodor.isacsson@gmail.com>

* fix [examples] - gaussian_cloning

* fix [examples] - gate_teleportation

use the .par attribute of a measured parameter

Co-authored-by: Theodor <theodor.isacsson@gmail.com>

examples/gate_teleportation.py

@@ -28,12 +28,12 @@
     # compare against the expected output
     # X(q1/sqrt(2)).F.P(0.5).X(q0/sqrt(0.5)).F.|z>
     # not including the corrections
-    Squeezed(0.1) | q[3]
-    Fourier       | q[3]
-    Xgate(q[0])   | q[3]
-    Pgate(0.5)    | q[3]
-    Fourier       | q[3]
-    Xgate(q[1])   | q[3]
+    Squeezed(0.1)   | q[3]
+    Fourier         | q[3]
+    Xgate(q[0].par) | q[3]
+    Pgate(0.5)      | q[3]
+    Fourier         | q[3]
+    Xgate(q[1].par) | q[3]
     # end circuit
 
 results = eng.run(gate_teleportation)

examples/gaussian_cloning.py

@@ -8,9 +8,13 @@
 eng = sf.Engine(backend="gaussian")
 gaussian_cloning = sf.Program(4)
 
+alpha = 0.7+1.2j
+r = np.abs(alpha)
+phi = np.angle(alpha)
+
 with gaussian_cloning.context as q:
     # state to be cloned
-    Coherent(0.7+1.2j) | q[0]
+    Coherent(r, phi) | q[0]
 
     # 50-50 beamsplitter
     BS = BSgate(pi/4, 0)
@@ -50,4 +54,4 @@
 
 print("Fidelity of cloned state:", np.mean(f))
 print("Mean displacement of cloned state:", np.mean(a))
-print("Mean covariance matrix of cloned state:", np.cov([a.real, a.imag]))
+print("Mean covariance matrix of cloned state:\n", np.cov([a.real, a.imag]))

examples/teleportation.py

@@ -1,41 +1,51 @@
 #!/usr/bin/env python3
 import strawberryfields as sf
-from strawberryfields.ops import *
-from strawberryfields.utils import scale
+from strawberryfields.ops import (
+    Coherent,
+    Squeezed,
+    BSgate,
+    Xgate,
+    Zgate,
+    MeasureX,
+    MeasureP,
+)
+
+import numpy as np
 from numpy import pi, sqrt
 
-# initialize engine and program objects
-eng = sf.Engine(backend="gaussian")
-teleportation = sf.Program(3)
-
-with teleportation.context as q:
-    psi, alice, bob = q[0], q[1], q[2]
-
-    # state to be teleported:
-    Coherent(1+0.5j) | psi
-
-    # 50-50 beamsplitter
-    BS = BSgate(pi/4, 0)
-
-    # maximally entangled states
-    Squeezed(-2) | alice
-    Squeezed(2) | bob
-    BS | (alice, bob)
-
-    # Alice performs the joint measurement
-    # in the maximally entangled basis
-    BS | (psi, alice)
-    MeasureX | psi
-    MeasureP | alice
-
-    # Bob conditionally displaces his mode
-    # based on Alice's measurement result
-    Xgate(psi.par*sqrt(2)) | bob
-    Zgate(alice.par*sqrt(2)) | bob
-    # end circuit
-
-results = eng.run(teleportation)
-# view Bob's output state and fidelity
-print(results.samples)
-print(results.state.displacement([2]))
-print(results.state.fidelity_coherent([0, 0, 1+0.5j]))
+# set the random seed
+np.random.seed(42)
+
+prog = sf.Program(3)
+
+alpha = 1 + 0.5j
+r = np.abs(alpha)
+phi = np.angle(alpha)
+
+with prog.context as q:
+    # prepare initial states
+    Coherent(r, phi) | q[0]
+    Squeezed(-2) | q[1]
+    Squeezed(2) | q[2]
+
+    # apply gates
+    BS = BSgate(pi / 4, pi)
+    BS | (q[1], q[2])
+    BS | (q[0], q[1])
+
+    # Perform homodyne measurements
+    MeasureX | q[0]
+    MeasureP | q[1]
+
+    # Displacement gates conditioned on
+    # the measurements
+    Xgate(sqrt(2) * q[0].par) | q[2]
+    Zgate(sqrt(2) * q[1].par) | q[2]
+
+eng = sf.Engine("fock", backend_options={"cutoff_dim": 15})
+result = eng.run(prog)
+
+# view output state and fidelity
+print(result.samples)
+print(result.state)
+print(result.state.fidelity_coherent([0, 0, alpha]))