# Quantum Optical Experiments Modeled by Long Short-Term Memory

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## Abstract

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## 1. Introduction

## 2. Methods

#### 2.1. Target Values

#### 2.2. Loss Function

#### 2.3. Network Architecture

## 3. Experiments

#### 3.1. Dataset

#### 3.2. Workflow

#### 3.3. Results

## 4. Outlook

## 5. Conclusions

## Author Contributions

## Funding

## Data Availability Statement

## Acknowledgments

## Conflicts of Interest

## References

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**Figure 1.**Sequence processing model for a many-to-one mapping. The target value $\widehat{y}$ can be either an estimate for ${y}_{\mathrm{E}}$ (entanglement classification) or ${y}_{\mathrm{SRV}}$ (SRV regression).

**Figure 2.**Negative and positive samples in the data set as a function of the leading Schmidt rank n.

**Figure 3.**Workflow. We split the entire data by their leading Schmidt rank n. All samples with $n\ge 9$ constitute the extrapolation set, which we use to explore the out-of-distribution capabilities of our model. For the remaining samples (i.e., $n<9$), we make a random test split at a ratio of $1/4$. The test set is used to estimate the conventional generalization error of our model. We use the training set to perform cluster cross validation.

**Figure 4.**True negative rate (TNR), true positive rate (TPR), rediscovery ratio of the LSTM network using cluster cross validation for different folds 0–8. True negative rates are high for all validation folds. All metrics are good for the extrapolation set 9–12, demonstrating that the models perform well on data beyond the training set distribution, covering only leading Schmidt rank numbers 0–8. Error bars represent $95\phantom{\rule{0.166667em}{0ex}}\%$ binomial proportion confidence intervals.

**Figure 5.**(

**a**) True negative rate, (

**b**) true positive rate, (

**c**) rediscovery ratio, and (

**d**) precision for the extrapolation set 9–12 for varying sigmoid threshold $\tau $ and SRV radius r. For too restrictive parameter choices ($\tau \to 1$ and $r\to 0.5$), the TNR and precision approach the value 1, while TPR and rediscovery ratio approach 0, such that no interesting new setups would be identified. For too loose choices (small $\tau $, large r), too few negative samples would be rejected, such that the advantage over random search becomes negligible, reflected in smaller precision values. Hence, there is a trade-off between rediscovery ratio (diversity of discoveries) and precision (speed of discoveries). For a large variety of $\tau $ and r, the models perform satisfyingly well, allowing a decent compromise between TNR and TPR. This is also reflected by a value of 0.64 for the mean average precision, where the mean is taken over $r=0.5$ to $r=7$ with a step size of 0.1, and the average precision is over $\tau =1$ to $\tau =0$, with a step size of 0.01 for each value of r.

**Table 1.**Cluster cross validation folds (0–8) and extrapolation set (9–12) characterized by leading Schmidt rank n. Samples with $n=0$ and samples with $n=1$ are combined and then split into two folds (0,1) at random.

0,1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9–12 |

0,1 |

**Table 2.**Conventional in-distribution training and test errors. The test set consists of 20 % of the data. Performance on predicting the entanglement is measured using the BCE loss, TNR, and TPR. Performance on predicting the SRV is measured using the SRV loss according to Equation (2), SRV accuracy, and the mean distance between true SRV and predicted SRV.

Training | Test | |
---|---|---|

BCE loss | 10.2 | 10.4 |

TNR | 0.9271 ± 2.4 $\times {10}^{-4}$ | 0.9261 ± 3.8 $\times {10}^{-4}$ |

TPR | 0.9469 ± 4.1 $\times {10}^{-4}$ | 0.9427 ± 6.5 $\times {10}^{-4}$ |

SRV loss | 2.247 | 2.24 |

SRV accuracy | 0.9382 | 0.938 |

SRV mean distance | 1.3943 | 1.4 |

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**MDPI and ACS Style**

Adler, T.; Erhard, M.; Krenn, M.; Brandstetter, J.; Kofler, J.; Hochreiter, S. Quantum Optical Experiments Modeled by Long Short-Term Memory. *Photonics* **2021**, *8*, 535.
https://doi.org/10.3390/photonics8120535

**AMA Style**

Adler T, Erhard M, Krenn M, Brandstetter J, Kofler J, Hochreiter S. Quantum Optical Experiments Modeled by Long Short-Term Memory. *Photonics*. 2021; 8(12):535.
https://doi.org/10.3390/photonics8120535

**Chicago/Turabian Style**

Adler, Thomas, Manuel Erhard, Mario Krenn, Johannes Brandstetter, Johannes Kofler, and Sepp Hochreiter. 2021. "Quantum Optical Experiments Modeled by Long Short-Term Memory" *Photonics* 8, no. 12: 535.
https://doi.org/10.3390/photonics8120535