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Register a new userTransfer of Phase Information between Optical and Microwave Fields via an Electron Spin
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We demonstrate the coherent coupling and the resulting transfer of phase information between microwave and optical fields in a single nitrogen vacancy center in diamond. The relative phase of two microwave fields is encoded in a coherent superposition spin state. This phase information is then retrieved with a pair of optical fields. A related process is also used for the transfer of phase information from optical to microwave fields. These studies show the essential role of dark states, including optical pumping into the dark states, in the coherent microwave-optical coupling and open the door to the full quantum state transfer between microwave and optical fields in a solid-state spin ensemble.
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Squeezed light finds many important applications in quantum information science and quantum metrology, and has been produced in a variety of physical systems involving optical nonlinear processes. Here, we show how a nonlinear magnetostrictive interaction in a ferrimagnet in cavity magnomechanics can be used to reduce quantum noise of the electromagnetic field. We show optimal parameter regimes where a substantial and stationary squeezing of the microwave output field can be achieved. The scheme can be realized within the reach of current technology in cavity electromagnonics and magnomechanics. Our work provides a new and practicable approach for producing squeezed vacuum states of electromagnetic fields, and may find promising applications in quantum information processing and quantum metrology.
A challenge in building large-scale superconducting quantum processors is to find the right balance between coherence, qubit addressability, qubit-qubit coupling strength, circuit complexity and the number of required control lines. Leading all-microwave approaches for coupling two qubits require comparatively few control lines and benefit from high coherence but suffer from frequency crowding and limited addressability in multi-qubit settings. Here, we overcome these limitations by realizing an all-microwave controlled-phase gate between two transversely coupled transmon qubits which are far detuned compared to the qubit anharmonicity. The gate is activated by applying a single, strong microwave tone to one of the qubits, inducing a coupling between the two-qubit $|f,grangle$ and $|g,erangle$ states, with $|grangle$, $|erangle$, and $|frangle$ denoting the lowest energy states of a transmon qubit. Interleaved randomized benchmarking yields a gate fidelity of $97.5pm 0.3 %$ at a gate duration of $126,rm{ns}$, with the dominant error source being decoherence. We model the gate in presence of the strong drive field using Floquet theory and find good agreement with our data. Our gate constitutes a promising alternative to present two-qubit gates and could have hardware scaling advantages in large-scale quantum processors as it neither requires additional drive lines nor tunable couplers.
Coherent conversion of microwave and optical photons in the single-quantum level can significantly expand our ability to process signals in various fields. Efficient up-conversion of a feeble signal in the microwave domain to the optical domain will lead to quantum-noise-limited microwave amplifiers. Coherent exchange between optical photons and microwave photons will also be a stepping stone to realize long-distance quantum communication. Here we demonstrate bidirectional and coherent conversion between microwave and light using collective spin excitations in a ferromagnet. The converter consists of two harmonic oscillator modes, a microwave cavity mode and a magnetostatic mode called Kittel mode, where microwave photons and magnons in the respective modes are strongly coupled and hybridized. An itinerant microwave field and a travelling optical field can be coupled through the hybrid system, where the microwave field is coupled to the hybrid system through the cavity mode, while the optical field addresses the hybrid system through the Kittel mode via Faraday and inverse Faraday effects. The conversion efficiency is theoretically analyzed and experimentally evaluated. The possible schemes for improving the efficiency are also discussed.
A quantum memory at microwave frequencies, able to store the state of multiple superconducting qubits for long times, is a key element for quantum information processing. Electronic and nuclear spins are natural candidates for the storage medium as their coherence time can be well above one second. Benefiting from these long coherence times requires to apply the refocusing techniques used in magnetic resonance, a major challenge in the context of hybrid quantum circuits. Here we report the first implementation of such a scheme, using ensembles of nitrogen-vacancy (NV) centres in diamond coupled to a superconducting resonator, in a setup compatible with superconducting qubit technology. We implement the active reset of the NV spins into their ground state by optical pumping and their refocusing by Hahn echo sequences. This enables the storage of multiple microwave pulses at the picoWatt level and their retrieval after up to $35 mu$s, a three orders of magnitude improvement compared to previous experiments.
In this paper we investigate an implementation of a quantum gate for quantum information processing in a system of quantum dots in an optical cavity manipulated by collinear laser fields. For simplicity we give theoretical and numerical results only for simulations of two quantum dots in a cavity interacting with two collinear fields. Extension to the system of many quantum dots in a cavity can be done in similar manner as the two dots system. It is shown that due to the collinear fields are used, a two qubit gate operation can be acheived by choosing properly detunings and amplitudes of the collinear fields.
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