Quantum Datasets

PennyLane provides the data subpackage to download, create, store and manipulate quantum datasets, where the quantum dataset is a collection of quantum data obtained from various quantum systems that describe it and its evolution.

Note

The packages zstd and dill are required to use the data module. These can be installed with pip install zstd dill.

Loading Datasets in PennyLane

We can access data of a desired type with the load() or load_interactive() functions. These download the desired datasets or load them from local storage if previously downloaded.

To specify the dataset to be loaded, the data category (data_name) must be specified, alongside category-specific keyword arguments. For the full list of available datasets, please see the datasets website. The load() function returns a list with the desired data.

>>> H2datasets = qml.data.load("qchem", molname="H2", basis="STO-3G", bondlength=1.1)
>>> print(H2datasets)
[<Dataset = description: qchem/H2/STO-3G/1.1, attributes: ['molecule', 'hamiltonian', ...]>]
>>> H2data = H2datasets[0]

We can load datasets for multiple parameter values by providing a list of values instead of a single value. To load all possible values, use the special keyword “full”.

>>> H2datasets = qml.data.load("qchem", molname="H2", basis="full", bondlength=[0.5, 1.1])
>>> print(H2datasets)
[<Dataset = description: qchem/H2/6-31G/0.5, attributes: ['molecule', 'hamiltonian', ...]>,
 <Dataset = description: qchem/H2/6-31G/1.1, attributes: ['molecule', 'hamiltonian', ...]>,
 <Dataset = description: qchem/H2/STO-3G/0.5, attributes: ['molecule', 'hamiltonian', ...]>,
 <Dataset = description: qchem/H2/STO-3G/1.1, attributes: ['molecule', 'hamiltonian', ...]>]

When we only want to download portions of a large dataset, we can specify the desired properties (referred to as attributes). For example, we can download or load only the molecule and energy of a dataset as follows:

>>> part = qml.data.load("qchem", molname="H2", basis="STO-3G", bondlength=1.1,
...                      attributes=["molecule", "fci_energy"])[0]
>>> part.molecule
<pennylane.qchem.molecule.Molecule at 0x7f56c9d78e50>
>>> part.fci_energy
-1.0791924385860894

To determine what attributes are available for a type of dataset, we can use the function list_attributes():

>>> qml.data.list_attributes(data_name="qchem")
["molecule",
"hamiltonian",
"sparse_hamiltonian",
...
"tapered_hamiltonian",
"full"]

Note

“full” is the default value for attributes, and it means that all available attributes for the Dataset will be downloaded.

Using Datasets in PennyLane

Once loaded, one can access properties of the datasets:

>>> H2data.molecule
<pennylane.qchem.molecule.Molecule object at 0x7f890b409280>
>>> print(H2data.hf_state)
[1 1 0 0]

The loaded data items are fully compatible with PennyLane. We can therefore use them directly in a PennyLane circuits as follows:

>>> dev = qml.device("default.qubit",wires=4)
>>> @qml.qnode(dev)
... def circuit():
...     qml.BasisState(H2data.hf_state, wires = [0, 1, 2, 3])
...     for op in H2data.vqe_gates:
...         qml.apply(op)
...     return qml.expval(H2data.hamiltonian)
>>> print(circuit())
-1.0791430411076344

Dataset Structure

You can call the list_datasets() function to get a snapshot of the currently available data. This function returns a nested dictionary as we show below.

>>> available_data = qml.data.list_datasets()
>>> available_data.keys()
dict_keys(["qspin", "qchem"])
>>> available_data["qchem"].keys()
dict_keys(["H2", "LiH", ...])
>>> available_data['qchem']['H2'].keys()
dict_keys(["6-31G", "STO-3G"])
>>> print(available_data['qchem']['H2']['STO-3G'])
["0.5", "0.54", "0.62", "0.66", ...]

Note that this example limits the results of the function calls for clarity and that as more data becomes available, the results of these function calls will change.

Creating Custom Datasets

The functionality in data also includes creating and reading custom-made datasets. We can use custom datasets to store any data generated in PennyLane and its supporting data. To create a dataset, we can do the following:

>>> coeffs = [1, 0.5]
>>> observables = [qml.PauliZ(wires=0), qml.PauliX(wires=1)]
>>> H = qml.Hamiltonian(coeffs, observables)
>>> energies, _ = np.linalg.eigh(qml.matrix(H)) #Calculate the energies
>>> dataset = qml.data.Dataset(data_name = "Example", hamiltonian=H, energies=energies)
>>> dataset.data_name
"Example"
>>> dataset.hamiltonian
(0.5) [X1]
+ (1) [Z0]
>>> dataset.energies
array([-1.5, -0.5,  0.5,  1.5])

We can then write this Dataset to storage and read it as follows:

>>> dataset.write("./path/to/dataset.dat")
>>> read_dataset = qml.data.Dataset()
>>> read_dataset.read("./path/to/dataset.dat")
>>> read_dataset.data_name
"Example"
>>> read_dataset.hamiltonian
(0.5) [X1]
+ (1) [Z0]
>>> read_dataset.energies
array([-1.5, -0.5,  0.5,  1.5])

Quantum Datasets Functions and Classes

Classes

Dataset

Create a dataset object to store a collection of information describing a physical system and its evolution.

Functions

list_datasets

Returns a dictionary of the available datasets.

list_attributes

List the attributes that exist for a specific data_name.

load

Downloads the data if it is not already present in the directory and return it to user as a Dataset object.

load_interactive

Download a dataset using an interactive load prompt.