Periodic Reporting for period 2 - QUITAR (Quantum Information Transduction with Acoustic Resonators)
Berichtszeitraum: 2022-10-01 bis 2024-03-31
Advances in the field of quantum information are rapidly improving our ability to create and control increasingly complex quantum devices that can have capabilities beyond what is possible in the classical world. These devices may one day be able to more efficiently simulate complex systems, solve difficult problems such as factoring large numbers, or transmit encrypted information with greater security. Just like in a classical device, performing these complex tasks will likely require many different components working together while each playing a unique role. Local quantum processors based on superconducting (SC) microwave circuits are now capable of performing sophisticated tasks ranging from quantum simulation to quantum error correction. At the same time, low-loss quantum channels based on infrared (IR) light can transfer quantum information over long distances. However, the crucial link between these two systems that would allow for the realization of a quantum network is still missing.
The goal of the ERC-STG project QUITAR is to create a quantum transducer between SC circuits and IR light using a third quantum system: sound waves in a bulk acoustic wave resonator. It has been shown that these types of resonators couple efficiently to both SC circuits and IR light and can be used to store and manipulate quantum states of sound. By developing techniques for integrating optics, acoustics, and microwave circuits at cryogenic temperatures, the project aims to demonstrate the conversion of complex quantum states between the microwave and IR domains and use this capability to entangle remote SC quantum nodes. Reaching this goal will be the crucial first step toward using SC circuits to implement a quantum network for long-distance communications or to build a large-scale, modular quantum computer.
The goal of the ERC-STG project QUITAR is to create a quantum transducer between SC circuits and IR light using a third quantum system: sound waves in a bulk acoustic wave resonator. It has been shown that these types of resonators couple efficiently to both SC circuits and IR light and can be used to store and manipulate quantum states of sound. By developing techniques for integrating optics, acoustics, and microwave circuits at cryogenic temperatures, the project aims to demonstrate the conversion of complex quantum states between the microwave and IR domains and use this capability to entangle remote SC quantum nodes. Reaching this goal will be the crucial first step toward using SC circuits to implement a quantum network for long-distance communications or to build a large-scale, modular quantum computer.
In this first reporting period, we have successfully completed all of the tasks in work package 1 and one of the main objectives of work package 2. As part of work package 1, we have designed and built a Brillouin cavity optomechanics system that can operate at milliKelvin temperatures, and used it to measure a GHz frequency high-overtone bulk acoustic wave resonator (HBAR) in the quantum ground state. We overcame a number of significant technical challenges, including the alignment and vibration isolation of the optical system, and investigated the effect of laser heating on the HBAR's mechanical modes. We found that, even for average incident laser powers that are more than sufficient for the eventual goal of microwave-to-optical transduction, our mechanical mode remains below a thermal occupation of one phonon. This work has now been published in Physical Review Research.
As part of work package 2, we have investigated the effect of infrared radiation on superconducting qubits in a systematic way using a novel experimental setup. We were able to control the power and duration of a laser pulse along with its spatial location relative to a transmon superconducting qubit. Using this technique, we were able to study the effect of laser light on the qubit and observe the dynamics of the quasiparticles generated by the high-energy photons, and thereby estimate the amount of time it takes the qubit to recover from the detrimental effects of infrared photons. This not only gave us important information about the possible repetition rates and laser powers that are feasible for operating a quantum transducer, but also more general insight into the behavior of superconducting circuits under high energy radiation, which has important impacts in the field of quantum information science beyond this project.
As part of work package 2, we have investigated the effect of infrared radiation on superconducting qubits in a systematic way using a novel experimental setup. We were able to control the power and duration of a laser pulse along with its spatial location relative to a transmon superconducting qubit. Using this technique, we were able to study the effect of laser light on the qubit and observe the dynamics of the quasiparticles generated by the high-energy photons, and thereby estimate the amount of time it takes the qubit to recover from the detrimental effects of infrared photons. This not only gave us important information about the possible repetition rates and laser powers that are feasible for operating a quantum transducer, but also more general insight into the behavior of superconducting circuits under high energy radiation, which has important impacts in the field of quantum information science beyond this project.
During the remainder of the project, we will focus on implementing the complete microwave-to-optical quantum transducer device and using it to demonstrate coherent transduction of the state of superconducting qubit into an infrared photon. State of the art experiments have only shown readout of the qubit state using a classical optical state, and demonstrating the quantum nature of the transduced optical state is still an outstanding goal in the field. This will be the first main goal of the project, which we are planning to achieve as part of work package 3. Intermediate results toward this goal will include the first demonstration of a bulk acoustic wave resonator coupled to both a superconducting qubit and infrared light, together with characterization of its quantum coherence properties, transduction efficiency, and noise properties. This will likely also lead to the development of new material platforms that exhibit new combinations of useful properties, such as large piezoelectric and photoelastic constants together with low acoustic, microwave, and optical losses.
If these the above goals are achieved, we will go on to demonstrate a telecomm-frequency link between two superconducting circuits in different cryostats. This would require overcoming additional challenges such as maintaining the coherence of the superconducting circuit during the entire transduction process, but would constitute a major milestone in building a quantum network of remote superconducting quantum processors.
If these the above goals are achieved, we will go on to demonstrate a telecomm-frequency link between two superconducting circuits in different cryostats. This would require overcoming additional challenges such as maintaining the coherence of the superconducting circuit during the entire transduction process, but would constitute a major milestone in building a quantum network of remote superconducting quantum processors.