Merge pull request #384 from Strilanc/dev

Version 2.1

html/quirk.template.html

@@ -35,7 +35,7 @@
                  
                  
                  
-                <span style="color:#BBB">Version 2.0</span>
+                <span style="color:#BBB">Version 2.1</span>
             </div>
 
             <!-- Circuit drawing area -->

package.json

@@ -3,7 +3,7 @@
   "title": "Quirk",
   "description": "A drag-and-drop toy for exploring and understanding small quantum circuits.",
   "license": "Apache-2.0",
-  "version": "2.0.0",
+  "version": "2.1.0",
   "homepage": "https://github.com/Strilanc/Quirk",
   "bugs": {
     "url": "https://github.com/Strilanc/Quirk/issues"

src/circuit/KetShaderUtil.js

@@ -86,20 +86,31 @@ const ketShaderPermute = (head, body, span=null) => ketShader(
     span);
 
 /**
- * @param {!String} head
- * @param {!String} body
- * @param {null|!int=null} span
+ * Returns a shader that multiplies each of the amplitudes in a superposition by computed phase factors.
+ *
+ * @param {!String} head Header code defining shader methods, uniforms, etc.
+ * @param {!String} body The body of a shader method returning the number of radians to phase by.
+ * @param {null|!int=null} span The number of qubits this operation applies to, if known ahead of time.
  * @return {!{withArgs: !function(args: ...!WglArg) : !WglConfiguredShader}}
  */
 const ketShaderPhase = (head, body, span=null) => ketShader(
-    head + `vec2 _ketgen_phase_for(float out_id) { ${body} }`,
-    'return cmul(amp, _ketgen_phase_for(out_id));',
+    `${head}
+        float _ketgen_phase_for(float out_id) {
+            ${body}
+        }
+    `,
+    `
+        float angle = _ketgen_phase_for(out_id);
+        return cmul(amp, vec2(cos(angle), sin(angle)));
+    `,
     span);
 
 /**
- * @param {!CircuitEvalContext} ctx
- * @param {undefined|!int=undefined} span
- * @param {undefined|!Array.<!string>} input_letters
+ * Determines some arguments to give to a shader produced by one of the ketShader methods.
+ *
+ * @param {!CircuitEvalContext} ctx The context in which the ket shader is being applied.
+ * @param {undefined|!int=undefined} span The number of qubits this shader applies to (if wasn't known ahead of time).
+ * @param {undefined|!Array.<!string>} input_letters The input gates that this shader cares about.
  * @returns {!Array.<!WglArg>}
  */
 function ketArgs(ctx, span=undefined, input_letters=[]) {

src/gates/CycleBitsGates.js

@@ -85,8 +85,8 @@ CycleBitsGates.CycleBitsFamily = Gate.buildFamily(2, 16, (span, builder) => buil
 CycleBitsGates.ReverseCycleBitsFamily = Gate.buildFamily(2, 16, (span, builder) => builder.
     setSerializedId(">>" + span).
     setSymbol(">>>").
-    setSymbol("Right Rotate").
-    setTitle("Rotates bits upward.").
+    setTitle("Right Rotate").
+    setBlurb("Rotates bits upward.").
     setDrawer(cyclePainter(true)).
     setTooltipMatrixFunc(() => makeCycleBitsMatrix(-1, span)).
     setActualEffectToShaderProvider(ctx => cycleBitsShader(ctx, span, -1)).

src/gates/FourierTransformGates.js

@@ -35,8 +35,7 @@ const CONTROLLED_PHASE_GRADIENT_SHADER = ketShaderPhase(
     `
         float hold = floor(out_id * 2.0 / span);
         float step = mod(out_id, span / 2.0);
-        float angle = hold * step * factor * 6.2831853071795864769 / span;
-        return vec2(cos(angle), sin(angle));
+        return hold * step * factor * 6.2831853071795864769 / span;
     `);
 
 const FOURIER_TRANSFORM_MATRIX_MAKER = span =>

src/gates/MultiplyAccumulateGates.js

@@ -154,4 +154,4 @@ MultiplyAccumulateGates.all = [
     ...MultiplyAccumulateGates.SquareSubtractInputFamily.all,
 ];
 
-export {MultiplyAccumulateGates, BIG_MUL_MOD_SHADER_CODE}
+export {MultiplyAccumulateGates, BIG_MUL_MOD_SHADER_CODE, MUL_STEP}

src/gates/ParametrizedRotationGates.js

@@ -71,8 +71,7 @@ const Z_TO_A_SHADER = ketShaderPhase(
         ${ketInputGateShaderCode('A')}
     `,
     `
-        float angle = read_input_A() * out_id * factor / _gen_input_span_A;
-        return vec2(cos(angle), sin(angle));
+        return read_input_A() * out_id * factor / _gen_input_span_A;
     `);
 
 ParametrizedRotationGates.XToA = new GateBuilder().

src/gates/PhaseGradientGates.js

@@ -12,16 +12,32 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+import {Config} from "src/Config.js";
 import {Gate} from "src/circuit/Gate.js"
 import {GatePainting} from "src/draw/GatePainting.js"
 import {ketArgs, ketShaderPhase} from "src/circuit/KetShaderUtil.js"
+import {MUL_STEP} from "src/gates/MultiplyAccumulateGates.js"
 import {WglArg} from "src/webgl/WglArg.js"
 
 const PHASE_GRADIENT_SHADER = ketShaderPhase(
-    'uniform float factor;',
     `
-        float angle = out_id * factor;
-        return vec2(cos(angle), sin(angle));
+        uniform float factor;
+
+        /// Scales an angle by an integer factor.
+        /// Performs the multiplication gradually, to avoid losing precision.
+        float angle_mul(float base_angle, float whole_factor) {
+            float result = 0.0;
+            for (int k = 0; k < ${Math.ceil(Config.MAX_WIRE_COUNT/MUL_STEP)}; k++) {
+                result += base_angle * mod(whole_factor, ${1<<MUL_STEP}.0);
+                result = mod(result, 6.283185307179586476925286766559);
+                whole_factor = floor(whole_factor / ${1<<MUL_STEP}.0);
+                base_angle = mod(base_angle * ${1<<MUL_STEP}.0, 6.283185307179586476925286766559);
+            }
+            return result;
+        }
+    `,
+    `
+        return angle_mul(factor, out_id);
     `);
 
 let PhaseGradientGates = {};

src/gates/PostSelectionGates.js

@@ -55,7 +55,7 @@ PostSelectionGates.PostSelectOn = new GateBuilder().
 /** @type {!Gate} */
 PostSelectionGates.PostSelectAntiX = new GateBuilder().
     setSerializedId("|+⟩⟨+|").  // The +/- drawing convention was switched, but the serialized id must stay the same.
-    setSymbol("|-⟩⟨-|").
+    setSymbol("|⊖⟩⟨⊖|").
     setTitle("Postselect X-Off").
     setBlurb("Keeps ON+OFF states, discards/retries ON-OFF states.").
     setDrawer(POST_SELECT_DRAWER).
@@ -65,7 +65,7 @@ PostSelectionGates.PostSelectAntiX = new GateBuilder().
 /** @type {!Gate} */
 PostSelectionGates.PostSelectX = new GateBuilder().
     setSerializedId("|-⟩⟨-|").  // The +/- drawing convention was switched, but the serialized id must stay the same.
-    setSymbol("|+⟩⟨+|").
+    setSymbol("|⊕⟩⟨⊕|").
     setTitle("Postselect X-On").
     setBlurb("Keeps ON-OFF states, discards/retries ON+OFF states.").
     setDrawer(POST_SELECT_DRAWER).
@@ -75,7 +75,7 @@ PostSelectionGates.PostSelectX = new GateBuilder().
 /** @type {!Gate} */
 PostSelectionGates.PostSelectAntiY = new GateBuilder().
     setSerializedId("|X⟩⟨X|").  // The cross/slash convention was switched, but the serialized id must stay the same.
-    setSymbol("|/⟩⟨/|").
+    setSymbol("|⊘⟩⟨⊘|").
     setTitle("Postselect Y-Off").
     setBlurb("Keeps ON+iOFF states, discards ON-iOFF states.").
     setDrawer(POST_SELECT_DRAWER).
@@ -85,7 +85,7 @@ PostSelectionGates.PostSelectAntiY = new GateBuilder().
 /** @type {!Gate} */
 PostSelectionGates.PostSelectY = new GateBuilder().
     setSerializedId("|/⟩⟨/|").  // The cross/slash convention was switched, but the serialized id must stay the same.
-    setSymbol("|X⟩⟨X|").
+    setSymbol("|⊗⟩⟨⊗|").
     setTitle("Postselect Y-On").
     setBlurb("Keeps ON-iOFF states, discards/retries ON+iOFF states.").
     setDrawer(POST_SELECT_DRAWER).

test/circuit/CircuitStats.test.js

@@ -16,6 +16,7 @@ import {Suite, assertThat, assertTrue} from "test/TestUtil.js"
 import {CircuitStats} from "src/circuit/CircuitStats.js"
 
 import {CircuitDefinition} from "src/circuit/CircuitDefinition.js"
+import {Complex} from "src/math/Complex.js"
 import {GateColumn} from "src/circuit/GateColumn.js"
 import {Gates} from "src/gates/AllGates.js"
 import {Matrix} from "src/math/Matrix.js"
@@ -41,7 +42,7 @@ const circuit = (diagram, ...extras) => CircuitDefinition.fromTextDiagram(new Ma
     ['-', undefined],
     ['+', undefined],
     ['|', undefined],
-    ['/', undefined]
+    ['/', null]
 ]), diagram);
 
 suite.testUsingWebGL("empty", () => {
@@ -117,7 +118,7 @@ suite.testUsingWebGL('incoherent-amplitude-display', () => {
 suite.testUsingWebGL('coherent-amplitude-display', () => {
     let c = circuit(`-H-•-a/--
                      ---X-//--
-                     -H-------`, ['a', Gates.Displays.AmplitudeDisplayFamily.ofSize(2)]);
+                     -H-------`, ['a', Gates.Displays.AmplitudeDisplayFamily]);
     let stats = CircuitStats.fromCircuitAtTime(c, 0);
     assertThat(stats.qubitDensityMatrix(Infinity, 0)).isApproximatelyEqualTo(Matrix.square(0.5, 0, 0, 0.5));
     assertThat(stats.qubitDensityMatrix(Infinity, 1)).isApproximatelyEqualTo(Matrix.square(0.5, 0, 0, 0.5));
@@ -141,7 +142,7 @@ suite.testUsingWebGL('conditional-bloch-display', () => {
 
 suite.testUsingWebGL('probability-display', () => {
     let c = circuit(`-H-•-%-
-                     ---X-/-`, ['%', Gates.Displays.ProbabilityDisplayFamily.ofSize(2)]);
+                     ---X-/-`, ['%', Gates.Displays.ProbabilityDisplayFamily]);
     let stats = CircuitStats.fromCircuitAtTime(c, 0);
     assertThat(stats.qubitDensityMatrix(Infinity, 0)).isApproximatelyEqualTo(Matrix.square(0.5, 0, 0, 0.5));
     assertThat(stats.customStatsForSlot(5, 0)).isApproximatelyEqualTo(
@@ -151,15 +152,15 @@ suite.testUsingWebGL('probability-display', () => {
 suite.testUsingWebGL('controlled-multi-probability-display', () => {
     let c = circuit(`---◦-
                      -H-%-
-                     ---/-`, ['%', Gates.Displays.ProbabilityDisplayFamily.ofSize(2)]);
+                     ---/-`, ['%', Gates.Displays.ProbabilityDisplayFamily]);
     let stats = CircuitStats.fromCircuitAtTime(c, 0);
     assertThat(stats.customStatsForSlot(3, 1)).isApproximatelyEqualTo(
         Matrix.col(0.5, 0.5, 0, 0));
 });
 
 suite.testUsingWebGL('density-display', () => {
     let c = circuit(`-d/-
-                     -//-`, ['d', Gates.Displays.DensityMatrixDisplayFamily.ofSize(2)]);
+                     -//-`, ['d', Gates.Displays.DensityMatrixDisplayFamily]);
     let stats = CircuitStats.fromCircuitAtTime(c, 0);
     assertThat(stats.customStatsForSlot(1, 0)).isApproximatelyEqualTo(
         Matrix.square(
@@ -172,7 +173,7 @@ suite.testUsingWebGL('density-display', () => {
 suite.testUsingWebGL('shifted-density-display', () => {
     let c = circuit(`----
                      -d/-
-                     -//-`, ['d', Gates.Displays.DensityMatrixDisplayFamily.ofSize(2)]);
+                     -//-`, ['d', Gates.Displays.DensityMatrixDisplayFamily]);
     let stats = CircuitStats.fromCircuitAtTime(c, 0);
     assertThat(stats.customStatsForSlot(1, 1)).isApproximatelyEqualTo(
         Matrix.square(
@@ -262,3 +263,31 @@ suite.testUsingWebGL('survival-rates-controlled-postselection', () => {
     assertThat(stats.survivalRate(13)).isApproximatelyEqualTo(0.5);
     assertThat(stats.survivalRate(14)).isApproximatelyEqualTo(0.5);
 });
+
+suite.testUsingWebGL('dynamic-phase-gradient-keeps-qubits-coherent', () => {
+    let stats = CircuitStats.fromCircuitAtTime(
+        circuit(`-H-P-
+                 -H-/-
+                 -H-/-
+                 -H-/-
+                 -H-/-
+                 -H-/-
+                 -H-/-
+                 -H-/-
+                 -H-/-
+                 -H-/-
+                 -H-/-
+                 -H-/-
+                 -H-/-
+                 -H-/-
+                 -H-/-
+                 -H-/-`, ['P', Gates.PhaseGradientGates.DynamicPhaseGradientFamily]),
+        0.9);
+
+    // Check coherence of each qubit.
+    for (let i = 0; i < 16; i++) {
+        let [x, y, z] = stats.qubitDensityMatrix(Infinity, i).qubitDensityMatrixToBlochVector();
+        let r = x*x + y*y + z*z;
+        assertThat(r).withInfo({i, x, y, z}).isApproximatelyEqualTo(1);
+    }
+});

test/circuit/KetShaderUtil.test.js

@@ -49,7 +49,7 @@ suite.testUsingWebGL("ketShaderPermute", () => {
 suite.testUsingWebGL("ketShaderPhase", () => {
     let shader = ketShaderPhase(
         '',
-        'return vec2(cos(out_id/10.0), sin(out_id/10.0));',
+        'return out_id/10.0;',
         3);
     assertThatCircuitShaderActsLikeMatrix(
         ctx => shader.withArgs(...ketArgs(ctx)),