# Bell state measurement strange behaviour

**URL:** <https://discuss.pennylane.ai/t/bell-state-measurement-strange-behaviour/1194>\
**Category:** PennyLane Development\
**Created:** [July 13, 2021, 5:45pm UTC](https://discuss.pennylane.ai/t/bell-state-measurement-strange-behaviour/1194 "2021-07-13T17:45:14Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![qgertrud](https://avatars.discourse-cdn.com/v4/letter/q/35a633/32.png) [@qgertrud](https://discuss.pennylane.ai/u/qgertrud)\
**Post date:** [July 13, 2021, 5:45pm UTC](https://discuss.pennylane.ai/t/bell-state-measurement-strange-behaviour/1194/1 "2021-07-13T17:45:14Z")

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Hi, I was exploring some of the experimental parts of PennyLane and found something strange happening!

When creating a Bell state, the outcomes of running a quantum circuit on the tensor device are not as expected. As we are either sampling the |00\> or the |11\> states, I’d expect to get the same outcomes each time! This is not the case here:

```python
import pennylane as qml

def circuit():
    qml.Hadamard(wires=0)
    qml.CNOT(wires=[0, 1])
    return [qml.sample(qml.PauliZ(i)) for i in range(2)]

dev = qml.device("default.tensor", wires=2, shots=10)
qnode = qml.QNode(circuit, dev)
qnode()

```

```auto
array([[1., -1., 1., -1., 1., -1., -1., 1., -1., 1.],
       [-1., -1., 1., 1., 1., 1., 1., 1., 1., 1.]])

```

Note: I was using `tensornetwork==0.4.0` and `PennyLane==0.16.0`.

---

<div class="post-metadata">

**Author:** ![Kuma-quant](https://yyz2.discourse-cdn.com/flex012/user_avatar/discuss.pennylane.ai/kuma-quant/32/582_2.png) [@Kuma-quant](https://discuss.pennylane.ai/u/Kuma-quant)\
**Post date:** [July 15, 2021, 10:58am UTC](https://discuss.pennylane.ai/t/bell-state-measurement-strange-behaviour/1194/2 "2021-07-15T10:58:52Z")

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It is bug found recently, and has not been fixed to date.

[Tensor network simulation method in qml.beta - PennyLane Help - Xanadu Discussion Forum](http://discuss.pennylane.ai/t/tensor-network-simulation-method-in-qml-beta/1129/3)