From fd2f47190dbe57721583e68d973144af5de773de Mon Sep 17 00:00:00 2001
From: Abhishek Bhatt <46929125+Abhishek-1Bhatt@users.noreply.github.com>
Date: Mon, 18 Sep 2023 00:26:55 -0400
Subject: [PATCH] Added Superdense endcoding and decoding circuits to
 CircuitZoo (#34)

---------

Co-authored-by: Stefan Krastanov <stefan@krastanov.org>
---
 Project.toml                                |  2 +-
 src/CircuitZoo/CircuitZoo.jl                | 71 +++++++++++++++++++++
 src/backends/quantumoptics/quantumoptics.jl |  1 +
 test/runtests.jl                            |  1 +
 test/test_circuitzoo_superdense.jl          | 22 +++++++
 5 files changed, 96 insertions(+), 1 deletion(-)
 create mode 100644 test/test_circuitzoo_superdense.jl

diff --git a/Project.toml b/Project.toml
index b505d9d4..61ec073c 100644
--- a/Project.toml
+++ b/Project.toml
@@ -39,7 +39,7 @@ PrecompileTools = "1"
 QuantumClifford = "0.8"
 QuantumInterface = "0.3.0"
 QuantumOptics = "1.0.5"
-QuantumOpticsBase = "0.4"
+QuantumOpticsBase = "0.4.14"
 QuantumSymbolics = "0.2.4"
 Reexport = "1.2.2"
 ResumableFunctions = "0.6.1"
diff --git a/src/CircuitZoo/CircuitZoo.jl b/src/CircuitZoo/CircuitZoo.jl
index 0e0b91a7..1e6133a3 100644
--- a/src/CircuitZoo/CircuitZoo.jl
+++ b/src/CircuitZoo/CircuitZoo.jl
@@ -851,4 +851,75 @@ function (circuit::PurifyExpedientNode)(purified,sacrificed...)
     [a..., b..., c..., d...]
 end
 
+"""
+$TYPEDEF
+
+Fields:
+
+$FIELDS
+
+The circuit for Superdense Coding to encode the 2 (classical) bit message
+to its corresponding bell pair representation. `reg` is a single qubit register containing
+Alice's half of the entangled bell pair and message is the 2 bit message Alice intends to send to Bob.
+Based on the 2 bit message the state of the qubit in the register is mutated in place with `apply!`
+
+```jldoctest
+julia> reg = Register(1)
+
+julia> initialize!(reg[1], Z1)
+
+julia> message = [1, 1]
+
+julia> SDEncode()(reg, message)
+```
+"""
+
+struct SDEncode <: AbstractCircuit
+end
+
+function (circuit::SDEncode)(reg, message)
+    if message[1] == 1
+        apply!(reg[1], Z)
+    end
+    if message[2] == 1
+        apply!(reg[1], X)
+    end
+end
+
+
+"""
+$TYPEDEF
+
+Fields:
+
+$FIELDS
+
+The circuit for Superdense Coding to decode the 2 (classical) bit message
+using the entangled bell pair stored in the registers regA and regB after Alice's encoding of the first qubit.
+Returns a Tuple of the decoded message.
+
+```jldoctest
+julia> regA = Register(1)
+
+julia> regB = Register(1)
+
+julia> initalize!(regA[1], Z1)
+
+julia> initalize!(regB[1], Z1)
+
+julia> SDDecode()(regA, regB)
+```
+"""
+
+struct SDDecode <: AbstractCircuit
+end
+
+function (circuit::SDDecode)(regA, regB)
+    apply!((regB[1], regA[1]), CNOT)
+    apply!(regB[1], H)
+    b1 = project_traceout!(regA, 1, Z)
+    b2 = project_traceout!(regB, 1, Z)
+    return b1-1, b2-1
+end
+
 end # module
diff --git a/src/backends/quantumoptics/quantumoptics.jl b/src/backends/quantumoptics/quantumoptics.jl
index 6ec699f6..d2b081b6 100644
--- a/src/backends/quantumoptics/quantumoptics.jl
+++ b/src/backends/quantumoptics/quantumoptics.jl
@@ -37,6 +37,7 @@ function observable(state::Union{<:Ket,<:Operator}, indices, operation)
     expect(op, state)
 end
 
+
 function project_traceout!(state::Union{Ket,Operator},stateindex,psis::Base.AbstractVecOrTuple{<:Ket})
     if nsubsystems(state) == 1 # TODO is there a way to do this in a single function, instead of _overlap vs _project_and_drop
         _overlaps = [_overlap(psi,state) for psi in psis]
diff --git a/test/runtests.jl b/test/runtests.jl
index 1b1e3c0a..9bc2c8f0 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -28,6 +28,7 @@ println("Starting tests with $(Threads.nthreads()) threads out of `Sys.CPU_THREA
 @doset "observable"
 @doset "noninstant_and_backgrounds_qubit"
 @doset "noninstant_and_backgrounds_qumode"
+@doset "circuitzoo_superdense"
 @doset "circuitzoo_purification"
 @doset "examples"
 get(ENV,"QUANTUMSAVORY_PLOT_TEST","")=="true" && @doset "plotting_cairo"
diff --git a/test/test_circuitzoo_superdense.jl b/test/test_circuitzoo_superdense.jl
new file mode 100644
index 00000000..c1ac0e77
--- /dev/null
+++ b/test/test_circuitzoo_superdense.jl
@@ -0,0 +1,22 @@
+using QuantumSavory
+using QuantumSavory.CircuitZoo: SDEncode, SDDecode
+using Test
+
+## Set up an entangled bell pair
+ra = Register(1)
+rb = Register(1)
+
+initialize!(ra[1], Z1)
+initialize!(rb[1], Z1)
+
+apply!(ra[1], H)
+apply!((ra[1], rb[1]), CNOT)
+
+# Random 2 bit classical message
+message = Tuple(rand(0:1, 2))
+
+# Use the circuits to encode and decode the message
+SDEncode()(ra, message)
+rec = SDDecode()(ra, rb)
+
+@test message == rec