Clarify order of measurements for locally-biased classical shadows

docs/tutorials/randomized_measurements.ipynb

@@ -126,7 +126,7 @@
    "source": [
     "from povm_toolbox.library import ClassicalShadows\n",
     "\n",
-    "# By default, the Classical Shadows (CS) measurement uses X,Y,Z measurements with equal probability.\n",
+    "# By default, the Classical Shadows (CS) measurement uses Z-,X-,Y-measurements with equal probability.\n",
     "cs_implementation = ClassicalShadows(num_qubits=num_qubits, seed=23)\n",
     "# Define the default shot budget.\n",
     "cs_shots = 4096\n",
@@ -150,15 +150,23 @@
    "source": [
     "from povm_toolbox.library import LocallyBiasedClassicalShadows\n",
     "\n",
-    "# Set the distributions of the shots among the X,Y,Z measurements.\n",
+    "# Set the distributions of the shots among the Z-,X-,Y-measurements (in this order).\n",
     "bias = np.array(\n",
     "    [\n",
-    "        [0.0000000028, 0.4408677642, 0.5591322330],  # bias for first qubit\n",
-    "        [0.1989721524, 0.3190601952, 0.4819676524],  # bias for second qubit\n",
+    "        [\n",
+    "            0.0000000028,  # bias for Z-measurements on first qubit\n",
+    "            0.4408677642,  # bias for X-measurements on first qubit\n",
+    "            0.5591322330,  # bias for Y-measurements on first qubit\n",
+    "        ],\n",
+    "        [\n",
+    "            0.1989721524,  # bias for Z-measurements on second qubit\n",
+    "            0.3190601952,  # bias for X-measurements on second qubit\n",
+    "            0.4819676524,  # bias for Y-measurements on second qubit\n",
+    "        ],\n",
     "    ]\n",
     ")\n",
     "\n",
-    "# The Locally-Biased Classical Shadows (LBCS) measurement uses X,Y,Z measurements with different probabilities.\n",
+    "# The Locally-Biased Classical Shadows (LBCS) measurement uses Z-,X-,Y-measurements with different probabilities.\n",
     "lbcs_implementation = LocallyBiasedClassicalShadows(num_qubits=num_qubits, bias=bias, seed=24)\n",
     "# Define the default shot budget.\n",
     "lbcs_shots = 4096\n",

povm_toolbox/library/locally_biased_classical_shadows.py

@@ -57,8 +57,10 @@ def __init__(
             num_qubits: the number of qubits.
             bias: can be either 1D or 2D. If 1D, it should contain float values indicating the bias
                 for measuring in each of the PVMs. I.e., its length equals the number of PVMs (3).
-                These floats should sum to 1. If 2D, it will have a new set of biases for each
-                qubit.
+                The first bias corresponds to the Z-measurement, the second bias to the
+                X-measurement and the third bias to the Y-measurement. These floats should sum to 1.
+                If 2D, the expected shape of the array is ``(num_qubits, 3)`` and a new set of
+                biases will be set for each qubit.
             measurement_layout: optional list of indices specifying on which qubits the POVM acts.
                 See :attr:`.measurement_layout` for more details.
             measurement_twirl: whether to randomly twirl the measurements. For each single-qubit

povm_toolbox/library/mutually_unbiased_bases_measurements.py

@@ -67,8 +67,8 @@ def __init__(
             num_qubits: the number of qubits.
             bias: can be either 1D or 2D. If 1D, it should contain float values indicating the bias
                 for measuring in each of the PVMs. I.e., its length equals the number of PVMs (3).
-                These floats should sum to 1. If 2D, it will have a new set of biases for each
-                qubit.
+                These floats should sum to 1. If 2D, the expected shape of the array is
+                ``(num_qubits, 3)`` and a new set of biases will be set for each qubit.
             angles: can be either 1D or 2D. If 1D, it should be of length 3 and contain float values
                 to indicate the three Euler angles to rotate the locally-biased classical shadows
                 (LBCS) measurement in the Bloch sphere representation. If 2D, it will have a new set

povm_toolbox/library/randomized_projective_measurements.py

@@ -89,8 +89,8 @@ def __init__(
             num_qubits: the number of qubits.
             bias: can be either 1D or 2D. If 1D, it should contain float values indicating the bias
                 for measuring in each of the PVMs. I.e., its length equals the number of PVMs.
-                These floats should sum to 1. If 2D, it will have a new set of biases for each
-                qubit.
+                These floats should sum to 1. If 2D, the expected shape of the array is
+                ``(num_qubits, num_pvms)`` and a new set of biases will be set for each qubit.
             angles: can be either 1D or 2D. If 1D, it should be a flatten array containing float
                 values to indicate the different angles of each PVM. I.e. its length equals two
                 times the number of PVMs (since we have 2 angles per PVM). If 2D, it will have a new