diff --git a/doc/Makefile b/doc/Makefile
new file mode 100644
index 0000000..d0c3cbf
--- /dev/null
+++ b/doc/Makefile
@@ -0,0 +1,20 @@
+# Minimal makefile for Sphinx documentation
+#
+
+# You can set these variables from the command line, and also
+# from the environment for the first two.
+SPHINXOPTS ?=
+SPHINXBUILD ?= sphinx-build
+SOURCEDIR = source
+BUILDDIR = build
+
+# Put it first so that "make" without argument is like "make help".
+help:
+ @$(SPHINXBUILD) -M help "$(SOURCEDIR)" "$(BUILDDIR)" $(SPHINXOPTS) $(O)
+
+.PHONY: help Makefile
+
+# Catch-all target: route all unknown targets to Sphinx using the new
+# "make mode" option. $(O) is meant as a shortcut for $(SPHINXOPTS).
+%: Makefile
+ @$(SPHINXBUILD) -M $@ "$(SOURCEDIR)" "$(BUILDDIR)" $(SPHINXOPTS) $(O)
diff --git a/doc/README.md b/doc/README.md
new file mode 100644
index 0000000..f673191
--- /dev/null
+++ b/doc/README.md
@@ -0,0 +1,2 @@
+# PyQuafu Documentation by Sphinx
+
diff --git a/doc/make.bat b/doc/make.bat
new file mode 100644
index 0000000..dc1312a
--- /dev/null
+++ b/doc/make.bat
@@ -0,0 +1,35 @@
+@ECHO OFF
+
+pushd %~dp0
+
+REM Command file for Sphinx documentation
+
+if "%SPHINXBUILD%" == "" (
+ set SPHINXBUILD=sphinx-build
+)
+set SOURCEDIR=source
+set BUILDDIR=build
+
+%SPHINXBUILD% >NUL 2>NUL
+if errorlevel 9009 (
+ echo.
+ echo.The 'sphinx-build' command was not found. Make sure you have Sphinx
+ echo.installed, then set the SPHINXBUILD environment variable to point
+ echo.to the full path of the 'sphinx-build' executable. Alternatively you
+ echo.may add the Sphinx directory to PATH.
+ echo.
+ echo.If you don't have Sphinx installed, grab it from
+ echo.https://www.sphinx-doc.org/
+ exit /b 1
+)
+
+if "%1" == "" goto help
+
+%SPHINXBUILD% -M %1 %SOURCEDIR% %BUILDDIR% %SPHINXOPTS% %O%
+goto end
+
+:help
+%SPHINXBUILD% -M help %SOURCEDIR% %BUILDDIR% %SPHINXOPTS% %O%
+
+:end
+popd
diff --git a/doc/source/apiref/apiref_0.3.5.rst b/doc/source/apiref/apiref_0.3.5.rst
index 8aed751..e9b1bfb 100644
--- a/doc/source/apiref/apiref_0.3.5.rst
+++ b/doc/source/apiref/apiref_0.3.5.rst
@@ -5,6 +5,8 @@ API Reference
This page is still under refinement, the contents you see may be incomplete at present.
+.. _quantum_circuit:
+
Quantum Circuit
------------------
@@ -17,7 +19,7 @@ Quantum Elements
.. hint::
hello
-.. autoclass:: quafu.elements.quantum_element.Instruction
+.. autoclass:: quafu.elements.Instruction
:members:
diff --git a/doc/source/conf.py b/doc/source/conf.py
new file mode 100644
index 0000000..23531d8
--- /dev/null
+++ b/doc/source/conf.py
@@ -0,0 +1,38 @@
+# Configuration file for the Sphinx documentation builder.
+#
+# For the full list of built-in configuration values, see the documentation:
+# https://www.sphinx-doc.org/en/master/usage/configuration.html
+
+# -- package path -------------------------------------------
+import sys
+import os
+
+package_path = os.path.join(os.getcwd(), '..\\..\\src\\')
+sys.path.insert(0, package_path)
+
+# -- Project information -----------------------------------------------------
+# https://www.sphinx-doc.org/en/master/usage/configuration.html#project-information
+
+project = 'PyQuafu-Docs'
+copyright = '2023, BAQIS-ScQ-Cloud'
+author = 'BAQIS-ScQ-Cloud'
+release = '0.3.6'
+
+# -- General configuration ---------------------------------------------------
+# https://www.sphinx-doc.org/en/master/usage/configuration.html#general-configuration
+
+extensions = ['sphinx.ext.autodoc',
+ 'sphinx.ext.napoleon'
+ ] # 'sphinx.ext.autosummary'
+
+templates_path = ['_templates']
+exclude_patterns = []
+
+# -- Options for HTML output -------------------------------------------------
+# https://www.sphinx-doc.org/en/master/usage/configuration.html#options-for-html-output
+
+html_theme = "sphinx_rtd_theme"
+html_static_path = ['_static']
+
+# Use Napoleon interpreter to support Google style docstrings
+autodoc_typehints = 'description'
diff --git a/doc/source/index.rst b/doc/source/index.rst
new file mode 100644
index 0000000..9bafb6b
--- /dev/null
+++ b/doc/source/index.rst
@@ -0,0 +1,28 @@
+.. PyQuafuDoc documentation master file, created by
+ sphinx-quickstart on Wed Sep 13 18:54:07 2023.
+ You can adapt this file completely to your liking, but it should at least
+ contain the root `toctree` directive.
+
+Welcome to PyQuafu's documentation!
+======================================
+
+`Quafu `_ shares open access to
+super-conducting quantum (ScQ) computing resources with public users from all around
+the world. As the python SDK of `Quafu `_, ``pyquafu``
+provides not only flexible and advanced interfaces to the experimental backends,
+but also useful toolkits for simulating, visualizing and more about quantum computation.
+This documentation describes its basic syntax and usages.
+
+Contents
+====================================
+.. toctree::
+ :maxdepth: 2
+
+ User Guide
+ API Reference
+ Historical Version
+
+Links
+====================================
+
+Quafu Cloud Platform: `http://quafu.baqis.ac.cn/ `_
diff --git a/doc/source/release_note/Release Notes - v0.3.6.md b/doc/source/release_note/Release Notes - v0.3.6.md
new file mode 100644
index 0000000..dff9f61
--- /dev/null
+++ b/doc/source/release_note/Release Notes - v0.3.6.md
@@ -0,0 +1,11 @@
+Release Notes - v0.3.6
+
+- Fixed bug of status code mixed up during receiving results.
+- Added attributes ``named_paras`` and ``named_pos`` into ``Instruction`` and all of its subclasses. This is to further unify interface of instructions. Added ``instructions`` into ``QuantumCircuit``, the former existing ``gates`` will contain only instances of ``QuantumGate`` in future.
+- Fixed some icon-missing bugs in ``CircuitPlotManager``, plots of all basic gates was tested.
+
+发布说明 - v0.3.6
+
+- 修复了接收结果时状态码混淆的bug。
+- 添加了属性 ``named_paras`` 和``named_pos`` 到 ``Instruction`` 和它的所有子类。这是为了进一步统一 ``Instruction`` 的接口。在 ``QuantumCircuit``中添加属性 ``instructions`` ，先前存在的``gates``在稍后的版本中将只包含``QuantumGate`` 的实例。
+- 修复了``CircuitPlotManager``中一些图标缺失的bug，测试了所有基本门的绘图。
\ No newline at end of file
diff --git a/doc/source/release_note/historical_version.rst b/doc/source/release_note/historical_version.rst
new file mode 100644
index 0000000..cee8bf2
--- /dev/null
+++ b/doc/source/release_note/historical_version.rst
@@ -0,0 +1,7 @@
+.. _historical_version:
+
+Historical Version
+==================
+
+.. note::
+ Historical version and release notes will be loaded later.
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diff --git a/doc/source/user_guide/quafu_doc_0.3.5/quafu_doc_0_3_5.rst b/doc/source/user_guide/quafu_doc_0.3.5/quafu_doc_0_3_5.rst
new file mode 100644
index 0000000..bb393ba
--- /dev/null
+++ b/doc/source/user_guide/quafu_doc_0.3.5/quafu_doc_0_3_5.rst
@@ -0,0 +1,613 @@
+User Guide
+==========
+
+.. note::
+ PyQuafu is under active development and this is user guide
+ for the latest version(0.3.5). If you are using ``pyquafu<=0.2``,
+ please see :ref:`historical_version`.
+
+Installation
+------------
+
+``pyquafu`` requires ``python>=3.8``. And it’s suggested to activate an
+individual virtual environment for it, see for axample
+`quafu-tutorial-venv `__.
+
+For the latest stable version, run the following codes in the command
+line/terminal:
+
+::
+
+ pip install pyquafu
+
+Set up your Quafu account
+-------------------------
+
+If you haven’t have an account, you may register on the
+`Quafu `__ website at first. Then you will
+find your apitoken ```` on the ``Dashboard`` page,
+which is required when you send tasks to ScQ-chips.
+
+By executing the following codes your token will be saved to your local
+device.
+
+.. code:: python
+
+ from quafu import User
+ user = User("")
+ user.save_apitoken()
+
+Once you’ve done this, you may look over the available ScQ-chips in the
+experimental backends.
+
+.. code:: python
+
+ available_backends = user.get_available_backends()
+
+::
+
+ system_name qubits status
+ ScQ-P10 10 Online
+ ScQ-P18 18 Online
+ ScQ-P136 136 Online
+
+*Note*: The next time you visit ``pyquafu``, you don’t have to save the
+token again. Yet a quafu token is not permanently validating, from time
+to time you may click **``refresh``** to get a new one on
+`Quafu `__ webpage .
+
+Build your first quantum circuit
+--------------------------------
+
+Let’s start by initializing a circuit with 5 qubits,
+
+.. code:: python
+
+ import numpy as np
+ from quafu import QuantumCircuit
+
+ qc = QuantumCircuit(5)
+
+Apply Gates
+~~~~~~~~~~~
+
+``PyQuafu`` supports ‘``qc.name(args)``’ style to apply gates and also
+other instructions.
+
+.. code:: python
+
+ qc.x(0)
+ qc.x(1)
+ qc.cnot(2, 1)
+ qc.ry(1, np.pi/2)
+ qc.rx(2, np.pi)
+ qc.rz(3, 0.1)
+ qc.cz(2, 3)
+
+::
+
+
+
+Alternatively, you may manually instantiate a gate and add it to the
+circuit.
+
+.. code:: python
+
+ # equivalent to qc.x(0)
+ import quafu.elements.element_gates as qeg
+ gate = qeg.XGate(pos=0)
+ qc.add_gate(gate)
+
+This is actually what ``.name(args)`` functions do. You would find
+the second style convenient when build a new circuit from existing one.
+
+For quantum gates Quafu supports, please check the API reference for :ref:`quantum_circuit`
+or use python-buitin ``dir()`` method.
+
+.. code:: python
+
+ print(dir(qc))
+
+::
+
+ ['__class__', '__delattr__', '__dict__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__getstate__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__le__', '__lt__', '__module__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', '__weakref__', '_used_qubits', 'add_gate', 'add_pulse', 'barrier', 'circuit', 'cnot', 'cp', 'cs', 'ct', 'cx', 'cy', 'cz', 'delay', 'draw_circuit', 'fredkin', 'from_openqasm', 'gates', 'h', 'id', 'iswap', 'layered_circuit', 'mcx', 'mcy', 'mcz', 'measure', 'measures', 'num', 'openqasm', 'p', 'plot_circuit', 'rx', 'rxx', 'ry', 'ryy', 'rz', 'rzz', 's', 'sdg', 'sw', 'swap', 'sx', 'sxdg', 'sy', 'sydg', 't', 'tdg', 'to_openqasm', 'toffoli', 'unitary', 'used_qubits', 'w', 'x', 'xy', 'y', 'z']
+
+Measure
+~~~~~~~
+
+Add measurement information including qubits measured (``measures``) and
+the classical bits keeping the measured results (``cbits``). If there is
+no measurement information provided, all qubits are measured by default.
+
+.. code:: python
+
+ measures = [0, 1, 2, 3, 4]
+ cbits = [0, 1, 2, 4, 3]
+ qc.measure(measures, cbits=cbits)
+ qc.measures
+
+::
+
+ {0: 0, 1: 1, 2: 2, 3: 4, 4: 3}
+
+Visualize
+~~~~~~~~~
+
+From ``version=0.3.2``, ``PyQuafu`` provides two similiar ways to
+visualize quantum circuits. You can draw the circuit using the
+``draw_circuit`` method and use ``width`` parameter to adjust the length of the circuit.
+
+.. code:: python
+
+ qc.draw_circuit(width=4)
+
+::
+
+ q[0] ------X--------X-------------------- M->c[0]
+
+ q[1] ------X--------+----RY(1.571)------- M->c[1]
+ |
+ q[2] ---------------*----RX(3.142)----*-- M->c[2]
+ |
+ q[3] --RZ(0.100)----------------------Z-- M->c[4]
+
+ q[4] ------------------------------------ M->c[3]
+
+Alternatively, you may create a figure by
+
+.. code:: python
+
+ qc.plot_circuit(title='A Quantum Circuit')
+
+|
+| |png|
+
+The latter visualization uses ``matplotlib`` as the backend and you may
+save the figure as any format that ``matplotlib`` supports.
+
+OPENQASM Support
+~~~~~~~~~~~~~~~~
+
+``pyquafu`` is backward compatible with quantum gates in
+`OPENQASM2.0 `__. You can store your
+quantum circuit as openqasm string, and also initialize your quantum
+circuit with openqasm text.
+
+.. code:: python
+
+ qasm = qc.to_openqasm()
+ print(qasm)
+
+::
+
+ OPENQASM 2.0;
+ include "qelib1.inc";
+ qreg q[5];
+ creg meas[5];
+ x q[0];
+ x q[1];
+ cx q[2],q[1];
+ ry(1.5707963267948966) q[1];
+ rx(3.141592653589793) q[2];
+ rz(0.1) q[3];
+ cz q[2],q[3];
+ x q[0];
+ measure q[0] -> meas[0];
+ measure q[1] -> meas[1];
+ measure q[2] -> meas[2];
+ measure q[3] -> meas[4];
+ measure q[4] -> meas[3];
+
+
+
+.. code:: python
+
+ del qc
+ qc = QuantumCircuit(5)
+ qc.from_openqasm(qasm)
+ qc.plot_circuit('Recovered from QASM')
+
+|
+| |image1|
+
+Execution and Simulation
+------------------------
+
+Now you are ready to submit the circuit to the experimental backend.
+First, initialize a Task object
+
+.. code:: python
+
+ from quafu import Task
+ task = Task()
+
+You can configure your task properties using the
+``config`` method. Here we
+choose the backend (``backend``) as ``ScQ-P18``, the single shots number
+(``shots``) as 2000 and compile the circuit on the backend
+(``compile``).
+
+.. code:: python
+
+ task.config(backend="ScQ-P18", shots=2000, compile=True)
+
+If you set the ``compile`` parameter to ``False``, make sure that you
+know the topology of the backend well and submit a valid circuit.
+
+Send the quantum circuit to the backend and wait for the results.
+
+.. code:: python
+
+ res = task.send(qc, wait=True)
+
+You can use the returned results to check the count and probability of
+each measured bit string. The output bits are arranged in **big-endian**
+convention by default, see also the next sectioin.
+
+.. code:: python
+
+ print(res.counts) #counts
+ print(res.probabilities) #probabilities
+ res.plot_probabilities()
+
+::
+
+ OrderedDict([('00100', 717), ('00110', 31), ('01000', 6), ('01100', 1185), ('01110', 39), ('10100', 22)])
+ {'00100': 0.3585, '00110': 0.0155, '01000': 0.003, '01100': 0.5925, '01110': 0.0195, '10100': 0.011}
+
+.. figure:: output_37_1.png
+ :alt: png
+
+ png
+
+The returned results contain also the **compiled circuit**, from which
+you may find optimization was made.
+
+.. code:: python
+
+ res.transpiled_circuit.plot_circuit("Compiled Circuit")
+
+|
+| |image2|
+
+If you want to check the correctness of the executed results. Quafu
+provide simple circuit similator
+
+.. code:: python
+
+ from quafu import simulate
+ simu_res = simulate(qc, output="probabilities")
+ simu_res.plot_probabilities()
+
+|
+| |image3|
+
+If you don’t want to plot the results for basis with zero probabilities,
+set the parameter ``full`` in method
+``plot_probabilities`` to False. Note that this parameter is only valid for results returned by
+the simulator.
+
+A Subtle detail
+~~~~~~~~~~~~~~~
+
+There are two different conventions when writing a computational basis
+as a bit-string. That is, for example, to denote the state where only
+the first qubit is excited, some may write 10…000 while others use
+000…01. This subtle detail sometimes causes confusion and even serious
+error in computation. The following experiment demonstrates conventions
+used in ``pyquafu``.
+
+.. code:: python
+
+ from quafu import QuantumCircuit, simulate
+
+ n = 3
+ qc = QuantumCircuit(n) # |000>
+ qc.h(0) # |100> + |000>
+ qc.measure()
+
+ res = simulate(qc)
+ res.plot_probabilities()
+
+|
+| |image4|
+
+Here you see that in ``pyquafu``, ``counts`` obeys so-called
+‘big-endian’. However, for some historical reasons, the state-vector use
+small-endian instead.
+
+.. code:: python
+
+ res = simulate(qc, output='state_vector')
+ print(res.state_vector[:2])
+ state_tensor = res.state_vector.reshape(tuple(n*[2])).transpose([-3, -2, -1])
+ print(state_tensor[0, 0, 0])
+ print(state_tensor[0, 0, 1])
+ print(state_tensor[1, 0, 0])
+
+::
+
+ [0.70710678+0.j 0.70710678+0.j]
+ (0.7071067811865475+0j)
+ (0.7071067811865475+0j)
+ 0j
+
+If this is not the convention you are used to, ``ndarray.transpose`` may
+help
+
+.. code:: python
+
+ state_tensor = state_tensor.transpose(tuple(range(n-1, -1, -1)))
+
+Measure observables
+-------------------
+
+Quafu provides measuring observables with an executed quantum circuit.
+You can input Pauli operators that need to measure expectation values to
+the ``submit`` `__ method. For
+example, you can input [[“XYX”, [0, 1, 2]], [“Z”, [1]]] to calculate the
+expectation of operators :math:`\sigma^x_0\sigma^y_1\sigma^x_2` and
+:math:`\sigma^z_1`. The
+``submit`` `__ method will
+minimize the executing times of the circuit with different measurement
+basis that can calculate all expectations of input operators.
+
+Here we show how to measure the energy expectation of the Ising chain
+
+.. math:: H=\sum_i \sigma^z_i \sigma^z_{i+1} + g \sum_i \sigma^x_i.
+
+First, we initialize a circuit with three Hadamard gate
+
+.. code:: python
+
+ q = QuantumCircuit(5)
+
+ for i in range(5):
+ if i % 2 == 0:
+ q.h(i)
+
+ measures = list(range(5))
+ q.measure(measures)
+ q.draw_circuit()
+
+::
+
+ q[0] --H-- M->c[0]
+
+ q[1] ----- M->c[1]
+
+ q[2] --H-- M->c[2]
+
+ q[3] ----- M->c[3]
+
+ q[4] --H-- M->c[4]
+
+Next, we set operators that need to be measured to calculate the energy
+expectation, and submit the circuit using
+``submit`` method
+
+.. code:: python
+
+ test_Ising = [["X", [i]] for i in range(5)]
+ test_Ising.extend([["ZZ", [i, i+1]] for i in range(4)])
+ res, obsexp = task.submit(q, test_Ising)
+
+::
+
+ Job start, need measured in [['XXXXX', [0, 1, 2, 3, 4]], ['ZZZZZ', [0, 1, 2, 3, 4]]]
+
+The function return measurement results and operator expectations. The
+measurement results only contain two ExecResult objects since the
+circuit is only executed twice, with measurement basis [[‘XXXXX’, [0, 1,
+2, 3, 4]] and [‘ZZZZZ’, [0, 1, 2, 3, 4]]] respectively.
+
+.. code:: python
+
+ res[0].plot_probabilities()
+ res[1].plot_probabilities()
+
+|
+| |image5|
+
+.. figure:: output_55_1.png
+ :alt: png
+
+ png
+
+The return operator expectations (``obsexp``) is a list with a length
+equal to the input operator number. We can use it to calculate the
+energy expectation
+
+.. code:: python
+
+ print(obsexp)
+ g = 0.5
+ E = g*sum(obsexp[:5])+sum(obsexp[5:])
+ print(E)
+
+::
+
+ [1.0, 0.046999999999999986, 1.0, 0.03699999999999998, 0.998, 0.00899999999999995, 0.08499999999999996, 0.08299999999999996, 0.008999999999999952]
+ 1.7269999999999999
+
+Submit task asynchronously
+--------------------------
+
+In the above examples, we chose opening python kernal and waiting for
+the result. You may also set the ``wait=False`` in
+``send`` function to submit
+the task asynchronously. Here we use another example that measures the
+qubit decoherence time :math:`T_1` to demonstrate the usage.
+
+.. code:: python
+
+ task = Task()
+ task.config(backend="ScQ-P10", shots=2000, compile=False, priority=2)
+
+Prepare parameters of a group of tasks and send the task asynchronously.
+
+.. code:: python
+
+ ts = range(0, 21, 1)
+ names = ["%dus" %t for t in ts]
+ for name, t in zip(names, ts):
+ q = QuantumCircuit(3)
+ q.x(2)
+ q.delay(2, t, unit="us")
+ q.measure([2])
+ res = task.send(q, wait=False, name=name, group="Q3_T1")
+
+Here the ``delay`` options will idle the target qubit ``2`` for a
+duration ``t`` in the time unit ``us`` (microsecond) and do nothing. In
+the send function, we set ``wait`` to false to execute the task
+asynchronously, give each task a name by duration time and set all tasks
+to a group named "Q3_T1".
+
+Now we can try to retrieve the group of tasks using the
+``retrieve_group``
+method.
+
+.. code:: python
+
+ group_res = task.retrieve_group("Q3_T1")
+ probs = [res.probabilities["1"] for res in group_res]
+
+::
+
+ Group: Q3_T1
+ task_id task_name status
+ 326564501AF5CF47 0us Completed
+ 32656450226701BD 1us Completed
+ 326564502A80CC5D 2us Completed
+ 3265645032D98C32 3us Completed
+ 326564503AEFE7EA 4us Completed
+ 326564600CFE2817 5us Completed
+ 3265646014FFEA5F 6us Completed
+ 326564601C2E9597 7us Completed
+ 32656460240A93E6 8us Completed
+ 326564602C15CFFB 9us Completed
+ 3265646033EEBD20 10us Running
+ 326564603B1A478D 11us In Queue
+ 3265647006C96D3D 12us In Queue
+ 326564700F71B85A 13us In Queue
+ 32656470204A3472 14us In Queue
+ 32656470384DCD98 15us In Queue
+ 3265648004FB6BCF 16us In Queue
+ 326564800DA63F54 17us In Queue
+ 3265648022DAC675 18us In Queue
+ 3265648036F7EA24 19us In Queue
+ 326564901AB566FF 20us In Queue
+
+Once all the tasks are completed, we can do the next step to get
+:math:`T_1`.
+
+.. code:: python
+
+ group_res = task.retrieve_group("Q3_T1")
+ probs = [res.probabilities["1"] for res in group_res]
+
+::
+
+ Group: Q3_T1
+ task_id task_name status
+ 326564501AF5CF47 0us Completed
+ 32656450226701BD 1us Completed
+ 326564502A80CC5D 2us Completed
+ 3265645032D98C32 3us Completed
+ 326564503AEFE7EA 4us Completed
+ 326564600CFE2817 5us Completed
+ 3265646014FFEA5F 6us Completed
+ 326564601C2E9597 7us Completed
+ 32656460240A93E6 8us Completed
+ 326564602C15CFFB 9us Completed
+ 3265646033EEBD20 10us Completed
+ 326564603B1A478D 11us Completed
+ 3265647006C96D3D 12us Completed
+ 326564700F71B85A 13us Completed
+ 32656470204A3472 14us Completed
+ 32656470384DCD98 15us Completed
+ 3265648004FB6BCF 16us Completed
+ 326564800DA63F54 17us Completed
+ 3265648022DAC675 18us Completed
+ 3265648036F7EA24 19us Completed
+ 326564901AB566FF 20us Completed
+
+.. code:: python
+
+ import matplotlib.pyplot as plt
+ from scipy.optimize import curve_fit
+ def func(x, a, b):
+ return a*np.exp(-b*x)
+
+ paras, pconv = curve_fit(func, ts, probs)
+ plt.plot(ts, probs, "o")
+ plt.plot(ts, func(ts, *paras), "--")
+ plt.xlabel("$t (\mu s)$")
+ plt.ylabel("prob")
+ plt.text(16, 0.9, r"$T_1=%.2f \mu s$" %(1/paras[1]))
+
+::
+
+ Text(16, 0.9, '$T_1=24.18 \\mu s$')
+
+|
+| |image6|
+
+Note that ``group_name`` and submite history are kept in the ``task``
+object only when ``python`` kernal is running. For data persistence, we
+provide ``TaskDatabase`` which use ``qslite3`` as the backend. It may
+help you to save task information to your local computer.
+
+We would not devote too much into developing ``TaskDatabase`` since the
+web-backends will prodive more powerful and convenient usages in the
+future. However, if you are interested in manipulating database freely
+by ``qslite3``, we do provide
+`tutorial `__
+for a quick start.
+
+.. code:: python
+
+ from quafu.tasks.task_database import QuafuTaskDatabase, print_task_info
+
+ with QuafuTaskDatabase() as db:
+ for res in group_res:
+ db.insert_task(res.taskid, res.task_status, group_name="Q3_T1", task_name=res.taskname, priority=2)
+ print('Tasks info stored')
+ print("Task list:")
+ for task_info in db.find_all_tasks():
+ print_task_info(task_info)
+ break # this is to avoid demo too long, you may cancel this line to view the whole info
+
+::
+
+ Tasks info stored
+ Task list:
+ Task ID: 326564501AF5CF47
+ Group Name: Q3_T1
+ Task Name: 0us
+ Status: Completed
+ Priority: 2
+ Send Time: None
+ Finish Time: None
+ ------------------------
+
+Finally, you can also retrieve a single task using its unique
+``task_id``, and download all the historical tasks in
+`Quafu `__ webpage.
+
+.. code:: python
+
+ res_20us = task.retrieve("1663B8403AE76050")
+ print(res_20us.probabilities)
+
+::
+
+ {'0': 0.662, '1': 0.338}
+
+.. |png| image:: output_23_0.png
+.. |image1| image:: output_28_0.png
+.. |image2| image:: output_39_0.png
+.. |image3| image:: output_41_0.png
+.. |image4| image:: output_45_0.png
+.. |image5| image:: output_55_0.png
+.. |image6| image:: output_67_1.png
diff --git a/quafu/elements/element_gates/clifford.py b/quafu/elements/element_gates/clifford.py
index c8fa0b9..0ca22c5 100644
--- a/quafu/elements/element_gates/clifford.py
+++ b/quafu/elements/element_gates/clifford.py
@@ -1,5 +1,9 @@
from .element_gates import HGate, SGate, CXGate
+"""
+TODO: add documentation about Clifford gates.
+"""
+
__all__ = ['HGate', 'SGate', 'CXGate']
diff --git a/src/qfvm_clifford/README.md b/src/qfvm_clifford/README.md
new file mode 100644
index 0000000..c23be0c
--- /dev/null
+++ b/src/qfvm_clifford/README.md
@@ -0,0 +1,67 @@
+# Clifford Simulator
+
+Usage of Clifford simulator in ``pyquafu`` is very similar with the default simulator, but applies only to circuits with a limited gate set.
+
+## Supported Gates
+
+### x
+
+The Pauli X gate. The bit flip gate.
+
+### y
+
+The Pauli Y gate.
+
+### z
+
+The Pauli Z gate. The phase flip gate
+
+### h
+
+The Hadamard gate. Swap the X and Z axes. Alternate name: `h_xz`
+
+### h_yz
+
+The variant of the Hadamard gate that swaps the Y and Z axes (instead of X and Z)
+
+### s
+
+Principal square root of Z gate. Phases the amplitue of |1> by i. Alternate name: `sqrt_z`
+
+### s_dag
+
+Adjoint of the principal square root of z gate. Phases the amplitube of |1> by -i. Alternate name: `sqrt_z_dag`
+
+### cnot
+
+The Z-controlled X gate. Applies an X gate to the target if the control is in the |1> state. Equivalently: negates the amplitude of the |1>|-> state. The first qubit is called the control, and the second qubit is the target. Alternate name: `cx`, `zcx`
+
+### swap
+
+Swap two qubits.
+
+### measure
+
+Z-basis measurement. Projects each target qubit into |0> or |1> and reports its value (false=|0>, true=|1>).
+
+### reset
+
+Z-basis reset. Forces each target qubit into the |0> state by silently measuring it in the Z basis and applying an X gate if it ended up in the |1> state.
+
+## Simple Example
+
+```python
+from quafu import QuantumCircuit, simulate
+
+qc = QuantumCircuit(4, 4)
+qc.x(0)
+qc.x(1)
+qc.measure([1, 2], [1, 0])
+qc.measure([3, 0], [2, 3])
+
+result = simulate(qc=qc, shots=10, simulator="qfvm_clifford", output="count_dict")
+counts = result.count
+
+# {"0101": 10}
+print(counts)
+```