Strong coupling of anEr3+-dopedYAlO3crystal to a superconducting resonator

Abstract

Quantum memories are integral parts of both quantum computers and quantum communication networks. Naturally, such a memory is embedded into a hybrid quantum architecture, which has to meet the requirements of fast gates, long coherence times and long distance communication. Erbium doped crystals are well suited as a microwave quantum memory for superconducting circuits with additional access to the optical telecom C-band around 1.55 µm. Here, we report on circuit QED experiments with an Er 3+ :YAlO3 crystal and demonstrate strong coupling to a superconducting lumped element resonator. The low magnetic anisotropy of the host crystal allows for attaining the strong coupling regime at relatively low magnetic fields, which are compatible with superconducting circuits. In addition, Ce 3+ impurities were detected in the crystal, which showed strong coupling as well.PACS numbers: 42.50. Fx, 76.30.Kg, 03.67.Hk, 03.67.Lx, Reliable operation of quantum information and communication protocols requires a quantum memory (QM), i.e. a system, which allows for storage and on-demand retrieval of a quantum bit [1,2]. This can be realized by a great variety of physical systems such as single trapped ions [3], atoms [4], single spins [5], two-level defects [6] and spin-ensembles [7], which differ by their frequency band, coherence time and operating conditions. Rare-earth (RE) ions doped into a solid represent one of most promising systems suitable for quantum memories, because their inner shell 4f optical electronic transitions possess very long coherence times [8]. The excellent optical properties of RE doped crystals are confirmed and harvested by the world wide research in quantum optics. This includes a light-matter interface at the single photon level [9], an efficient and broadband quantum memory for light [10,11], a quantum memory at the telecom Cband [12], an atomic frequency comb memory [13], storage of entanglement in a RE doped crystal [14] and generation of entanglement between two crystals [15]. Yet, in contrast to the single atom approach, a quantum memory based on RE doped solids allows for the implementation of multimode storage protocols [16,17].There are seven RE's ions (Ce 3+ , Nd 3+ , Sm 3+ , Gd 3+ , Dy 3+ , Er 3+ , Yb 3+ ), which are suited for a microwave quantum memory due to the presence of a large electronic spin associated with an unquenched orbital moment [18]. Most of them have access to the nuclear spin degrees of freedom, which allow for long term storage [19]. These RE ions can be doped into a variety of host crystals, and therefore, can potentially be integrated with superconducting (SC) quantum circuits [20]. The resulting hybrid quantum system can consist of a SC qubit, a transmission line or a resonator magnetically coupled to the spin ensemble [21]. The exclusive feature of some RE ions (Nd 3+ , Er 3+ , Yb 3+ ) is the presence of optical transitions inside standard telecommunication bands. A quantum memory based on these RE elements can be very attractive for quantum communication between qubits...

Microwave multimode memory with an erbium spin ensemble

“…The crystal is placed on top of a coplanar waveguide λ/2 microwave resonator fabricated on high-frequency laminate Rogers TMM 10i. In contrast to our previous investigations [20,22,23], a non-superconducting copper resonator is employed. Such a resonator does not perturb the magnetic DC field, therefore, we expect to attain a minimal inhomogeneous spin linewidth of the erbium spin ensemble.…”

“…In that respect, circuit Quantum Electrodynamics (QED) with RE doped crystals at the femtowatt power level and at milli-Kelvin temperatures presents a first step towards the implementation of a quantum memory [20,21]. A strong coupling regime accompanied with large collective coupling strength 30-200 MHz has been recently demonstrated [22][23][24]. However, reversible mapping of temporal microwave modes in a RE spin ensemble has not been shown.…”

“…On the basis of the cw spectroscopy, we performed time resolved ESR experiments in the temperature range 0.02-1 K. Due to the large mode volume of the resonator compared to the previous experiments with SC resonators [20,22,23], strong microwave pulses (1-10 mW) are necessary for coherent spin manipulation. Therefore, no additional cryogenic attenuation was used in the experiment, see Ref.…”

Coupling erbium spins to a three-dimensional superconducting cavity at zero magnetic field

“…3 that the linewidths of the hyperfine transitions are approximately Γ * /2π = 5 MHz. An ensemble of spins inside a cavity is usually modelled as a harmonic oscillator coupled to a cavity mode 8,14 .…”

Determining graphene's induced band gap with magnetic and electric emitters

“…They do not only show tunable magnetic and electric transitions from the MHz to the THz frequency range but also simultaneously allow for high position resolution [37]. Small band gaps can be investigated by cooling the system to the mK regime, such that magnetically tunable Zeeman [38] or hyperfine transitions [39] can be utilized. Our work can open additional pathways to enhance the fundamental understanding of the validity of different graphene models [24,40,41] and also provides relevant information for realistic applications and designs of interest, e.g., in atom-chip research [42][43][44].…”