Dynamics and Resonance Fluorescence from a Superconducting Artificial Atom Doubly Driven by Quantized and Classical Fields

  1. Xinhui Ruan,
  2. Jia-Heng Wang,
  3. Dong He,
  4. Pengtao Song,
  5. Shengyong Li,
  6. Qianchuan Zhao,
  7. L.M. Kuang,
  8. Jaw-Shen Tsai,
  9. Chang-Ling Zou,
  10. Jing Zhang,
  11. Dongning Zheng,
  12. O. V. Astafiev,
  13. Yu-xi Liu,
  14. and Zhihui Peng
We report an experimental demonstration of resonance fluorescence in a two-level superconducting artificial atom under two driving fields coupled to a detuned cavity. One of the fields
is classical and the other is varied from quantum (vacuum fluctuations) to classical one by controlling the photon number inside the cavity. The device consists of a transmon qubit strongly coupled to a one-dimensional transmission line and a coplanar waveguide resonator. We observe a sideband anti-crossing and asymmetry in the emission spectra of the system through a one-dimensional transmission line, which is fundamentally different from the weak coupling case. By changing the photon number inside the cavity, the emission spectrum of our doubly driven system approaches to the case when the atom is driven by two classical bichromatic fields. We also measure the dynamical evolution of the system through the transmission line and study the properties of the first-order correlation function, Rabi oscillations and energy relaxation in the system. The study of resonance fluorescence from an atom driven by two fields promotes understanding decoherence in superconducting quantum circuits and may find applications in superconducting quantum computing and quantum networks.

10-GHz superconducting cavity piezo-optomechanics for microwave-optical photon conversion

  1. Xu Han,
  2. Wei Fu,
  3. Changchun Zhong,
  4. Chang-Ling Zou,
  5. Yuntao Xu,
  6. Ayed Al Sayem,
  7. Mingrui Xu,
  8. Sihao Wang,
  9. Risheng Cheng,
  10. Liang Jiang,
  11. and Hong X. Tang
Coherent photon conversion between microwave and optics holds promise for the realization of distributed quantum networks, in particular, the architecture that incorporates superconducting
quantum processors with optical telecommunication channels. High-frequency gigahertz piezo-mechanics featuring low thermal excitations offers an ideal platform to mediate microwave-optical coupling. However, integrating nanophotonic and superconducting circuits at cryogenic temperatures to simultaneously achieve strong photon-phonon interactions remains a tremendous challenge. Here, we report the first demonstration of an integrated superconducting cavity piezo-optomechanical converter where 10-GHz phonons are resonantly coupled with photons in a superconducting microwave and a nanophotonic cavities at the same time. Benefited from the cavity-enhanced interactions, efficient bidirectional microwave-optical photon conversion is realized with an on-chip efficiency of 0.07% and an internal efficiency of 5.8%. The demonstrated superconducting piezo-optomechanical interface makes a substantial step towards quantum communication at large scale, as well as novel explorations in hybrid quantum systems such as microwave-optical photon entanglement and quantum sensing.

Magnon-photon strong coupling for tunable microwave circulators

  1. Na Zhu,
  2. Xu Han,
  3. Chang-Ling Zou,
  4. Mingrui Xu,
  5. and Hong X. Tang
We present a generic theoretical framework to describe non-reciprocal microwave circulation in a multimode cavity magnonic system and assess the optimal performance of practical circulatordevices. We show that high isolation (> 56 dB), extremely low insertion loss (< 0.05 dB), and flexible bandwidth control can be potentially realized in high-quality-factor superconducting cavity based magnonic platforms. These circulation characteristics are analyzed with materials of different spin densities. For high-spin-density materials such as yttrium iron garnet, strong coupling operation regime can be harnessed to obtain a broader circulation bandwidth. We also provide practical design principles for a highly integratible low-spin-density material (vanadium tetracyanoethylene) for narrow-band circulator operation, which could benefit noise-sensitive quantum microwave measurements. This theory can be extended to other coupled systems and provide design guidelines for achieving tunable microwave non-reciprocity for both classical and quantum applications.[/expand]

Radiative cooling of a superconducting resonator

  1. Mingrui Xu,
  2. Xu Han,
  3. Chang-Ling Zou,
  4. Wei Fu,
  5. Yuntao Xu,
  6. Changchun Zhong,
  7. Liang Jiang,
  8. and Hong X. Tang
Cooling microwave resonators to near the quantum ground state, crucial for their operation in the quantum regime, is typically achieved by direct device refrigeration to a few tens
of millikelvin. However, in quantum experiments that require high operation power such as microwave-to-optics quantum transduction, it is desirable to operate at higher temperatures with non-negligible environmental thermal excitations, where larger cooling power is available. In this Letter, we present a radiative cooling protocol to prepare a superconducting microwave mode near its quantum ground state in spite of warm environment temperatures for the resonator. In this proof-of-concept experiment, the mode occupancy of a 10-GHz superconducting resonator thermally anchored at 1.02~K is reduced to 0.44±0.05 by radiatively coupling to a 70-mK cold load. This radiative cooling scheme allows high-operation-power microwave experiments to work in the quantum regime, and opens possibilities for routing microwave quantum states to elevated temperatures.

Hardware-efficient quantum random access memory with hybrid quantum acoustic systems

  1. Connor T. Hann,
  2. Chang-Ling Zou,
  3. Yaxing Zhang,
  4. Yiwen Chu,
  5. Robert J. Schoelkopf,
  6. Steven M. Girvin,
  7. and Liang Jiang
Hybrid quantum systems in which acoustic resonators couple to superconducting qubits are promising quantum information platforms. High quality factors and small mode volumes make acoustic
modes ideal quantum memories, while the qubit-phonon coupling enables the initialization and manipulation of quantum states. We present a scheme for quantum computing with multimode quantum acoustic systems, and based on this scheme, propose a hardware-efficient implementation of a quantum random access memory (qRAM). Quantum information is stored in high-Q phonon modes, and couplings between modes are engineered by applying off-resonant drives to a transmon qubit. In comparison to existing proposals that involve directly exciting the qubit, this scheme can offer a substantial improvement in gate fidelity for long-lived acoustic modes. We show how these engineered phonon-phonon couplings can be used to access data in superposition according to the state of designated address modes–implementing a qRAM on a single chip.

Quantum generative adversarial learning in a superconducting quantum circuit

  1. Ling Hu,
  2. Shu-Hao Wu,
  3. Weizhou Cai,
  4. Yuwei Ma,
  5. Xianghao Mu,
  6. Yuan Xu,
  7. Haiyan Wang,
  8. Yipu Song,
  9. Dong-Ling Deng,
  10. Chang-Ling Zou,
  11. and Luyan Sun
Generative adversarial learning is one of the most exciting recent breakthroughs in machine learning—a subfield of artificial intelligence that is currently driving a revolution
in many aspects of modern society. It has shown splendid performance in a variety of challenging tasks such as image and video generations. More recently, a quantum version of generative adversarial learning has been theoretically proposed and shown to possess the potential of exhibiting an exponential advantage over its classical counterpart. Here, we report the first proof-of-principle experimental demonstration of quantum generative adversarial learning in a superconducting quantum circuit. We demonstrate that, after several rounds of adversarial learning, a quantum state generator can be trained to replicate the statistics of the quantum data output from a digital qubit channel simulator, with a high fidelity (98.8% on average) that the discriminator cannot distinguish between the true and the generated data. Our results pave the way for experimentally exploring the intriguing long-sought-after quantum advantages in machine learning tasks with noisy intermediate-scale quantum devices.

Superconducting cavity electro-optics: a platform for coherent photon conversion between superconducting and photonic circuits

  1. Linran Fan,
  2. Chang-Ling Zou,
  3. Risheng Cheng,
  4. Xiang Guo,
  5. Xu Han,
  6. Zheng Gong,
  7. Sihao Wang,
  8. and Hong X. Tang
Leveraging the quantum information processing ability of superconducting circuits and long-distance distribution ability of optical photons promises the realization of complex and large-scale
quantum networks. In such a scheme, a coherent and efficient quantum transducer between superconducting and photonic circuits is critical. However, such quantum transducer is still challenging since the use of intermediate excitations in current schemes introduces extra noise and limits bandwidth. Here we realize direct and coherent transduction between superconducting and photonic circuits based on triple-resonance electro-optics principle, with integrated devices incorporating both superconducting and optical cavities on the same chip. Electromagnetically induced transparency is observed, indicating the coherent interaction between microwave and optical photons. Internal conversion efficiency of 25.9\pm0.3\% has been achieved, with 2.05\pm0.04\% total efficiency. Superconducting cavity electro-optics offers broad transduction bandwidth and high scalability, and represents a significant step towards the integrated hybrid quantum circuits and distributed quantum computation.

Cat codes with optimal decoherence suppression for a lossy bosonic channel

  1. Linshu Li,
  2. Chang-ling Zou,
  3. Victor V. Albert,
  4. Sreraman Muralidharan,
  5. S. M. Girvin,
  6. and Liang Jiang
We investigate cat codes that can correct multiple excitation losses and identify two types of logical errors: bit-flip errors due to excessive excitation loss and dephasing errors
due to quantum back-action from the environment. We show that selected choices of logical subspace and coherent amplitude can efficiently reduce dephasing errors. The trade-off between the two major errors enables optimized performance of cat codes in terms of minimized decoherence. With high coupling efficiency, we show that one-way quantum repeaters with cat codes feature drastically boosted secure communication rate per mode compared with conventional encoding schemes, and thus showcase the promising potential of quantum information processing with continuous variable quantum codes.

Magnon dark modes and gradient memory

  1. Xufeng Zhang,
  2. Chang-Ling Zou,
  3. Na Zhu,
  4. Florian Marquardt,
  5. Liang Jiang,
  6. and Hong X. Tang
Extensive efforts have been expended in developing hybrid quantum systems to overcome the short coherence time of superconducting circuits by introducing the naturally long-lived spin
degree of freedom. Among all the possible materials, single-crystal yttrium iron garnet has shown up very recently as a promising candidate for hybrid systems, and various highly coherent interactions, including strong and even ultra-strong coupling, have been demonstrated. One distinct advantage of these systems is that the spins are in the form of well-defined magnon modes, which allows flexible and precise tuning. Here we demonstrate that by dissipation engineering, a non-Markovian interaction dynamics between the magnon and the microwave cavity photon can be achieved. Such a process enables us to build a magnon gradient memory to store information in the magnon dark modes, which decouple from the microwave cavity and thus preserve a long life-time. Our findings provide a promising approach for developing long-lifetime, multimode quantum memories.

Universal Control of an Oscillator with Dispersive Coupling to a Qubit

  1. Stefan Krastanov,
  2. Victor V. Albert,
  3. Chao Shen,
  4. Chang-Ling Zou,
  5. Reinier W. Heeres,
  6. Brian Vlastakis,
  7. Robert J. Schoelkopf,
  8. and Liang Jiang
We investigate quantum control of an oscillator mode off-resonantly coupled to an ancillary qubit. In the strong dispersive regime, we may drive the qubit conditioned on number states
of the oscillator, which together with displacement operations can achieve universal control of the oscillator. Based on our proof of universal control, we provide explicit constructions for arbitrary state preparation and arbitrary unitary operation of the oscillator. Moreover, we present an efficient procedure to prepare the number state ∣∣n⟩ using only O(n‾‾√) operations. We also compare our scheme with known quantum control protocols for coupled qubit-oscillator systems. This universal control scheme of the oscillator can readily be implemented using superconducting circuits.