From 71d97577aede9fb70ada9a0fc53f746dce075d93 Mon Sep 17 00:00:00 2001
From: AgustinVallejo <agustin.vallejo@udea.edu.co>
Date: Wed, 25 Dec 2024 12:04:12 -0500
Subject: [PATCH] Moving coefficients to the model
 https://github.com/phetsims/quantum-measurement/issues/54

---
 js/bloch-sphere/model/BlochSphereModel.ts     | 30 +++++++++++++++++++
 .../view/BlochSphereNumericalEquationNode.ts  | 16 +++++-----
 2 files changed, 38 insertions(+), 8 deletions(-)

diff --git a/js/bloch-sphere/model/BlochSphereModel.ts b/js/bloch-sphere/model/BlochSphereModel.ts
index e2b9ccf..88dd7e1 100644
--- a/js/bloch-sphere/model/BlochSphereModel.ts
+++ b/js/bloch-sphere/model/BlochSphereModel.ts
@@ -7,6 +7,7 @@
  * @author Agustín Vallejo (PhET Interactive Simulations)
  */
 
+import NumberProperty from '../../../../axon/js/NumberProperty.js';
 import TModel from '../../../../joist/js/TModel.js';
 import { EmptySelfOptions } from '../../../../phet-core/js/optionize.js';
 import PickRequired from '../../../../phet-core/js/types/PickRequired.js';
@@ -22,11 +23,40 @@ export default class BlochSphereModel implements TModel {
 
   public readonly blochSphere: ComplexBlochSphere;
 
+  // Coefficients of the state equation |psi> = upCoefficient |up> + downCoefficient * exp( i *  |down>
+  public readonly upCoefficientProperty: NumberProperty;
+  public readonly downCoefficientProperty: NumberProperty;
+  public readonly phaseFactorProperty: NumberProperty;
+
   public constructor( providedOptions: QuantumMeasurementModelOptions ) {
 
     this.blochSphere = new ComplexBlochSphere( {
       tandem: providedOptions.tandem.createTandem( 'blochSphere' )
     } );
+
+    this.upCoefficientProperty = new NumberProperty( 1, {
+      tandem: providedOptions.tandem.createTandem( 'upCoefficientProperty' ),
+      phetioReadOnly: true
+    } );
+
+    this.downCoefficientProperty = new NumberProperty( 0, {
+      tandem: providedOptions.tandem.createTandem( 'downCoefficientProperty' ),
+      phetioReadOnly: true
+    } );
+
+    this.phaseFactorProperty = new NumberProperty( 0, {
+      tandem: providedOptions.tandem.createTandem( 'phaseFactorProperty' ),
+      phetioReadOnly: true
+    } );
+
+    this.blochSphere.polarAngleProperty.link( theta => {
+      this.upCoefficientProperty.value = Math.cos( theta / 2 );
+      this.downCoefficientProperty.value = Math.sin( theta / 2 );
+    } );
+
+    this.blochSphere.azimutalAngleProperty.link( phi => {
+      this.phaseFactorProperty.value = phi / Math.PI;
+    } );
   }
 
   /**
diff --git a/js/bloch-sphere/view/BlochSphereNumericalEquationNode.ts b/js/bloch-sphere/view/BlochSphereNumericalEquationNode.ts
index ad6715a..2b0c490 100644
--- a/js/bloch-sphere/view/BlochSphereNumericalEquationNode.ts
+++ b/js/bloch-sphere/view/BlochSphereNumericalEquationNode.ts
@@ -33,16 +33,16 @@ export default class BlochSphereNumericalEquationNode extends HBox {
 
     const equationNode = new RichText( new DerivedStringProperty(
       [
-        model.blochSphere.polarAngleProperty,
-        model.blochSphere.azimutalAngleProperty
+        model.upCoefficientProperty,
+        model.downCoefficientProperty,
+        model.phaseFactorProperty
       ],
-      ( polarAngle: number, azimutalAngle: number ) => {
-        const upCoefficient = Utils.toFixed( Math.cos( polarAngle / 2 ), 2 );
-        const downCoefficient = Utils.toFixed( Math.abs( Math.sin( polarAngle / 2 ) ), 2 );
-        const downCoefficientSign = Math.sin( polarAngle / 2 ) < 0 ? '\u2212' : '+';
-        const azimutalCoefficient = Utils.toFixed( azimutalAngle / Math.PI, 2 );
+      ( upCoefficient: number, downCoefficient: number, phaseFactor: number ) => {
+        const upCoefficientString = Utils.toFixed( upCoefficient, 2 );
+        const downCoefficientString = Utils.toFixed( downCoefficient, 2 );
+        const azimutalCoefficientString = Utils.toFixed( phaseFactor, 2 );
 
-        return `|${PSI}⟩ = ${upCoefficient}|${UP}${KET} ${downCoefficientSign} ${downCoefficient}e<sup>i${azimutalCoefficient}${PI}</sup>|${DOWN}${KET}`;
+        return `|${PSI}⟩ = ${upCoefficientString}|${UP}${KET} + ${downCoefficientString}e<sup>i${azimutalCoefficientString}${PI}</sup>|${DOWN}${KET}`;
       }
     ), { font: EQUATION_FONT } );