Lightning Tensor device

The lightning.tensor device is a tensor network simulator device. The device is built on top of the cutensornet from the NVIDIA cuQuantum SDK, enabling GPU-accelerated simulation of quantum tensor network evolution.

A lightning.tensor device can be loaded simply using:

import pennylane as qml
dev = qml.device("lightning.tensor", wires=100)

By default, the device represents the quantum state approximated as a Matrix Product State (MPS). The default setup for the MPS tensor network approximation is:

• max_bond_dim (maximum bond dimension) defaults to 128 .

• cutoff (singular value truncation threshold) defaults to 0 .

• cutoff_mode (singular value truncation mode) defaults to abs , considering the absolute values of the singular values; Alternatively, users can opt to set cutoff_mode to rel to consider the relative values of the singular values.

The lightning.tensor device dispatches all operations to be performed on a CUDA-capable GPU of generation SM 7.0 (Volta) and greater.

Note

Given the inherent parallelism of GPUs, simulations with intensive parallel computation, such as those with larger maximum bond dimensions, stand to gain the most from the computational power offered by GPU and those simulations can benifit from the lightning.tensor device. It’s worth noting that if the bond dimension used in the simulation is small, the lightning.tensor device with MPS running a GPU may perform slower compared to a default.tensor device with MPS running on a CPU. For more details on how bond dimension affects the simulation performance, please refer to the Approximate Tensor Network Methods section in the cuQuantum SDK.

Users also have the flexibility to customize these parameters according to their specific needs with:

import pennylane as qml
import numpy as np

num_qubits = 100

device_kwargs_mps = {
    "max_bond_dim": 64,
    "cutoff": 1e-10,
    "cutoff_mode": "abs",
}

dev = qml.device("lightning.tensor", wires=num_qubits, method="mps", **device_kwargs_mps)

The lightning.tensor device allows users to get quantum circuit gradients using the parameter-shift method. This can be enabled at the PennyLane QNode level with:

@qml.qnode(dev, diff_method="parameter-shift")
def circuit(params):
    ...

Check out the Lightning-Tensor installation guide for more information.

See also

DefaultTensor for a CPU only tensor network simulator device.

Operations and observables support

The “lightning.tensor” supports 1- and 2-wire gate operations and all other operations that can be decomposed to that by PennyLane.

Supported operations:

BasisState	Prepares a single computational basis state.
CNOT	The controlled-NOT operator
ControlledPhaseShift	A qubit controlled phase shift.
ControlledQubitUnitary	Apply an arbitrary fixed unitary to wires with control from the control_wires.
CRot	The controlled-Rot operator
CRX	The controlled-RX operator
CRY	The controlled-RY operator
CRZ	The controlled-RZ operator
CSWAP	The controlled-swap operator
CY	The controlled-Y operator
CZ	The controlled-Z operator
DiagonalQubitUnitary	Apply an arbitrary diagonal unitary matrix with a dimension that is a power of two.
DoubleExcitation	Double excitation rotation.
ECR	An echoed RZX(pi/2) gate.
Hadamard	The Hadamard operator
Identity	The Identity operator
IsingXX	Ising XX coupling gate
IsingXY	Ising (XX + YY) coupling gate
IsingYY	Ising YY coupling gate
IsingZZ	Ising ZZ coupling gate
ISWAP	The i-swap operator
OrbitalRotation	Spin-adapted spatial orbital rotation.
PauliX	The Pauli X operator
PauliY	The Pauli Y operator
PauliZ	The Pauli Z operator
PhaseShift	Arbitrary single qubit local phase shift
PSWAP	Phase SWAP gate
QFT	Apply a quantum Fourier transform (QFT).
QubitCarry	Apply the QubitCarry operation to four input wires.
QubitSum	Apply a QubitSum operation on three input wires.
QubitUnitary	Apply an arbitrary unitary matrix with a dimension that is a power of two.
Rot	Arbitrary single qubit rotation
RX	The single qubit X rotation
RY	The single qubit Y rotation
RZ	The single qubit Z rotation
S	The single-qubit phase gate
SingleExcitation	Single excitation rotation.
SingleExcitationMinus	Single excitation rotation with negative phase-shift outside the rotation subspace.
SingleExcitationPlus	Single excitation rotation with positive phase-shift outside the rotation subspace.
SISWAP	The square root of i-swap operator.
SQISW	alias of SISWAP
SWAP	The swap operator
SX	The single-qubit Square-Root X operator.
T	The single-qubit T gate
Toffoli	Toffoli (controlled-controlled-X) gate.

Unsupported operations:

StatePrep	Prepare subsystems using the given ket vector in the computational basis.
QubitStateVector
DoubleExcitationMinus	Double excitation rotation with negative phase-shift outside the rotation subspace.
DoubleExcitationPlus	Double excitation rotation with positive phase-shift outside the rotation subspace.
GlobalPhase	A global phase operation that multiplies all components of the state by \(e^{-i \phi}\).
BlockEncode	Construct a unitary \(U(A)\) such that an arbitrary matrix \(A\) is encoded in the top-left block.

Supported observables:

The lightning.tensor supports all observables supported by the Lightning state-vector simulators, besides qml.SparseHamiltonian, qml.Projector and limited support to qml.Hamiltonian, qml.Prod.

Users can not create a Hamiltonian or Prod observable from Hamiltonian observables.

Exp	A symbolic operator representing the exponential of a operator.
Hadamard	The Hadamard operator
Hamiltonian	alias of LinearCombination
Hermitian	An arbitrary Hermitian observable.
Identity	The Identity operator
PauliX	The Pauli X operator
PauliY	The Pauli Y operator
PauliZ	The Pauli Z operator
Prod	Symbolic operator representing the product of operators.
SProd	Arithmetic operator representing the scalar product of an operator with the given scalar.
Sum	Symbolic operator representing the sum of operators.

Unsupported observables:

SparseHamiltonian	A Hamiltonian represented directly as a sparse matrix in Compressed Sparse Row (CSR) format.
Projector	Observable corresponding to the state projector \(P=\ket{\phi}\bra{\phi}\).

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