Tiny changes to a couple of URLs (quantumlib#5614)

Drop invalid bookmark and a redundant space.

Author: pavoljuhas

docs/experiments/fourier_checking.ipynb

@@ -872,7 +872,7 @@
     "[1] *Scott Aaronson. BQP and the Polynomial Hierarchy. STOC ’10, page 141–150, New York, NY, USA, 2010.* [arXiv](https://arxiv.org/pdf/0910.4698.pdf)\n",
     "\n",
     "[2] *Scott Aaronson and Andris Ambainis. Forrelation: A problem that optimally separates quantum\n",
-    "from classical computing. SIAM J. Comput., 47(3):982–1038, 2018.* [arXiv]( https://arxiv.org/pdf/1411.5729.pdf)"
+    "from classical computing. SIAM J. Comput., 47(3):982–1038, 2018.* [arXiv](https://arxiv.org/pdf/1411.5729.pdf)"
    ]
   }
  ],

docs/tutorials/google/identifying_hardware_changes.ipynb

@@ -722,7 +722,7 @@
     "\n",
     "*    You need to map your actual circuit's logical qubits to your selected hardware qubits. This is in general a difficult problem, and the best solution can depend on the specific structure of the circuit to be run. Take a look at the [Qubit Picking with Loschmidt Echoes](/cirq/tutorials/google/echoes.ipynb) tutorial, which estimates the error rates of gates for your specific circuit. Also, consider [Best Practices#qubit picking](/cirq/google/best_practices#qubit_picking) for additional advice on this.\n",
     "*    The [Optimization, Alignment, and Spin Echoes](/cirq/tutorials/google/spin_echoes.ipynb) tutorial provides resources on how you can improve the reliability of your circuit by: optimizing away redundant or low-impact gates, aligning gates into moments with others of the same type, and preventing decay on idle qubits with by adding spin echoes. \n",
-    "*    Other than for qubit picking, you should also use calibration for error compensation. The [XEB and Coherent Error](/cirq/noise/qcvv/xeb_coherent_noise.ipynb), [XEB Calibration Example](/cirq/noise/qcvv/xeb_calibration_example.ipynb), [Parallel XEB](/cirq/noise/qcvv/parallel_xeb.ipynb) and [Isolated XEB](/cirq/noise/qcvv/isolated_xeb.ipynb) tutorials demonstrate how to run a classical optimizer on collected two-qubit gate characterization data, identity the true unitary matrix implemented by each gate, and add [Virtual Pauli Z gates](/cirq/hardware/devices#virtual_z_gates) to compensate for the identified error, improving the reliability of your circuit.\n",
+    "*    Other than for qubit picking, you should also use calibration for error compensation. The [XEB and Coherent Error](/cirq/noise/qcvv/xeb_coherent_noise.ipynb), [XEB Calibration Example](/cirq/noise/qcvv/xeb_calibration_example.ipynb), [Parallel XEB](/cirq/noise/qcvv/parallel_xeb.ipynb) and [Isolated XEB](/cirq/noise/qcvv/isolated_xeb.ipynb) tutorials demonstrate how to run a classical optimizer on collected two-qubit gate characterization data, identity the true unitary matrix implemented by each gate, and add [Virtual Pauli Z gates](/cirq/hardware/devices) to compensate for the identified error, improving the reliability of your circuit.\n",
     "*    You are also free to use the characterization data to improve the performance of large batches of experiment circuits. In this case you'd want to prepare your characterization ahead of running all your circuits, and use the data to compensate each circuit, right before running them. See [Calibration FAQ](/cirq/noise/calibration_faq.md#i-have-many-circuits-to-calibrate-how-do-i-speed-it-up) for more information. "
    ]
   }