[WIP] Adds printer using qpic

src/phaseshift/bell_interferometer.py

@@ -31,6 +31,7 @@
 It was introduced in [this PR by Jake Bulmer and Yuan Yao](https://github.com/XanaduAI/strawberryfields/pull/584#issue-894649549).
 """
 
+from io import StringIO
 from collections import defaultdict
 from dataclasses import dataclass, field
 
@@ -444,3 +445,46 @@ def circuit_reconstruction(decomp: BellDecomp) -> NDArray[np.complex128]:
         U = phase_shifter(dim, mode, phi) @ U
 
     return U
+
+
+def circuit_printer(decomp, width=30, rounding=3):
+    """Print the circuit corresponding to the decomposition using qpic syntax.
+
+    Given a `BellDecomp` instance, this function prints the circuits in qpic format.
+    The `BellDecomp` instance can be obtained from the `bell_decomposition` function.
+
+    Args:
+        decomp (BellDecomp): The Bell decomposition containing the parameters of the circuit.
+
+    Returns:
+        ### NEED TO WRITE IT
+
+    Raises:
+        TypeError: If the input is not a BellDecomp instance.
+    """
+    output = StringIO()
+    dim = decomp.dim
+    # Apply the phase shifters at the input
+    for mode, phi in decomp.phi_input.items():
+        print(f"{mode} G ${round(phi/np.pi, rounding)}$ width={width}", file=output)
+
+    # Iterate through the layers of the circuit
+    for layer in range(dim):
+        # Apply the sMZIs in the layer
+        for mode in range(layer % 2, dim - 1, 2):
+            delta = round((decomp.delta[mode, layer] / np.pi) % 1, rounding)
+            sigma = round((decomp.sigma[mode, layer] / np.pi) % 1, rounding)
+            print(
+                f"{mode} {mode+1} G $\\genfrac{{}}{{}}{{0pt}}{{}}{{{delta}}}{{{sigma}}}$ width={width}",
+                file=output,
+            )
+        if (dim - 1, layer) in decomp.phi_edge:
+            phi_bottom = round((decomp.phi_edge[dim - 1, layer] / np.pi) % 1, rounding)
+            print(f"{dim-1} G ${phi_bottom}$ width={width}", file=output)
+    # Apply the phase shifters at the output
+    for mode, phi in decomp.phi_output.items():
+        phi = round((phi / np.pi) % 1, rounding)
+        print(f"{mode} G ${phi}$ width={width}", file=output)
+    captured_text = output.getvalue()
+    output.close()
+    return captured_text