Towards a Spin-Ensemble Quantum Memory for Superconducting Qubits (eBook)

Cécile Grèzes received the B.S. degree from the Ecole Normale supérieure, Paris, France, in 2009 and her Ph.D. from the University Paris VI in 2014. Her thesis work was performed at the Commissariat à l’énergie atomique on experimental quantum information processing with Josephson superconducting circuits and spins in crystal. Since 2015, she has been working on the development of nonvolatile magnetic memory in the electrical engineering department at the University of California Los Angeles.

Supervisor's Foreword 6
Acknowledgments 8
Abstract 9
Contents 11
1 Introduction 15
1.1 Rationale for the Hybrid Way 15
1.2 Spin Ensemble Quantum Memory Principle 18
1.3 Storing a Qubit State in a Spin Ensemble (Write) 20
1.4 Retrieving Few-Photon Fields Stored in a Spin Ensemble (Read) 24
1.5 NV Clock Transitions for Long Coherent Storage 27
1.6 Towards an Operational Quantum Memory 28
References 30
2 Background 33
2.1 Superconducting Circuits and Microwave Engineering 33
2.1.1 Superconducting Resonators 33
2.1.2 Josephson Junction Based Circuits 43
2.1.3 Circuit Quantum Electrodynamics 53
2.2 NV Center Spins in Diamond 59
2.2.1 Structure 59
2.2.2 The NV Center Spin Qubit 60
2.2.3 Coherence Times 65
2.3 Coupling Ensembles of NV Center Spins to Superconducting Circuits 67
2.3.1 Single Spin-Resonator Coupling 67
2.3.2 Spin Ensemble-Resonator Coupling: Collective Effects 68
2.3.3 The Resonator-Spins System in the Low-Excitation Regime 79
2.3.4 The Resonator-Spins System Under Strong Drive Powers 88
References 89
3 Proposal: A Spin Ensemble Quantum Memory for Superconducting Qubits 92
3.1 Spin-Based Quantum Memory 92
3.1.1 Motivations 92
3.1.2 Spin Ensemble Quantum Memory: Principles 93
3.2 Spin Ensemble Quantum Memory Protocol 95
3.2.1 The Write Step: Storage of N Quantum States |?1rangleƒ|?nrangle 95
3.2.2 The Read Step: On-Demand Retrieval of |?irangle 96
3.2.3 The Full Quantum Memory Protocol 99
3.3 Simulations 100
References 102
4 Experiment 1 (Write): Coherent Storage of Qubit States into a Spin Ensemble 105
4.1 State of the Art and Principle of the Experiment 105
4.1.1 State of the Art 105
4.1.2 Strong Coupling of NVs to a Superconducting Resonator 106
4.1.3 Principle of the Experiment 108
4.2 Experimental Realization 110
4.2.1 The Hybrid Quantum Circuit 110
4.2.2 Measurement Setup 116
4.3 Operating the Hybrid Quantum Circuit 122
4.3.1 Superconducting Circuit Characterization 122
4.3.2 Transferring Qubit States to the Bus Resonator 130
4.3.3 Coupling the NV Spin Ensemble to the Bus Resonator 132
4.4 Storage of Qubit States into a NV Spin Ensemble 134
4.4.1 Storing a Single Photon from the Qubit into the Spin Ensemble 134
4.4.2 Storing a Coherent Superposition from the Qubit to the Spin Ensemble 138
4.4.3 Entanglement Between the Spin Ensemble and the Resonator 141
4.5 Conclusions on Experiment 1: The Write Step 143
References 144
5 Experiment 2 (Read): Multimode Retrieval of Few Photon Fields from a Spin Ensemble 145
5.1 Principle of the Experiment 145
5.2 Experimental Realization 147
5.2.1 The Hybrid Quantum Circuit 147
5.2.2 Measurement Setup 151
5.3 Spectroscopy of the Resonator-Spins System 157
5.3.1 Characterization of the Resonator 158
5.3.2 System Spectroscopy at Zero-Magnetic Field 159
5.4 Active Reset of the Spins 162
5.4.1 Effect of Light Irradiation on the Superconducting Resonator 162
5.4.2 Continuous Irradiation: Dependence of the Spin Polarization on the Optical Power 168
5.4.3 Pulsed Irradiation: Active Spin Polarization 172
5.4.4 Spin Relaxation Time Measurement 177
5.5 Multimode Retrieval of Few Photon Fields Stored in a Spin Ensemble 178
5.5.1 Applying Hahn Echoes to the Spin Ensemble 178
5.5.2 Retrieval of Few-Photon Pulses Stored in the Spin Ensemble 186
5.6 NV Clock Transitions for Long Coherent Storage 193
5.6.1 Atomic Clock Transitions in NV Centers in Diamond 193
5.6.2 Full System Spectroscopy 194
5.6.3 Dependence of the Echo Coherence Time on the Magnetic Field 197
5.6.4 Advanced Analysis: Spin Classes Contributions to the Echo Decay 201
5.7 Conclusion on Experiment 2: The Read Step 207
References 209
6 Towards an Operational Quantum Memory 210
6.1 Reaching Efficient Memory Operations 210
6.1.1 Storage and Retrieval of Photon Fields at the Single Photon Level with Improved Efficiencies 210
6.1.2 Reaching the Operational Level 216
6.2 Running the Full Quantum Memory Protocol 218
6.2.1 Step 1/2: Realization of a Frequency Tunable Resonator Compatible with Refocusing Pulse Applications 218
6.2.2 Realizing a Hybrid Circuit Able to Run the Full Memory Protocol 226
References 229
7 Conclusions and Perspectives 230
References 232
Appendix AFabrication 233
Appendix BNV Center Distribution 235
Curriculum Vitae 238