Universal Unitary Transfer of Continuous-Variable Quantum States into a Few Qubits

Hastrup, Jacob; Park, Ki‐Min; Brask, Jonatan Bohr; Filip, Radim; Andersen, Ulrik L.

doi:10.1103/physrevlett.128.110503

Cited by 5 publications

(2 citation statements)

References 15 publications

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“…CPG: cubic phase gate, BS: beam splitter, QND: quantum non-demolition, PR: phase rotation, QC: quantum computation, QEC: quantum error correction, IQP: instantaneous quantum polynomial [69,70]. Conversions between discrete and continuous variables (CV-DV conversion) can also be achieved with the help of Rabi-type Hamiltonian gates [71].…”

Section: A Exact Decomposition Of Cubic Multi-mode Gatesmentioning

confidence: 99%

All-optical quantum computing using cubic phase gates

Budinger¹,

Furusawa²,

Loock³

2022

Preprint

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If suitable quantum optical interactions were available, transforming optical field mode operators in a nonlinear fashion, the all-photonics platform could be one of the strongest contenders for realizing a quantum computer. Unlike other, matter-based (solid-state or atomic) platforms, photonic qubits can be operated at room temperature and high clock rates (GHz or, in principle, even THz). In addition, recent continuous-variable time-domain approaches are extremely well scalable. Moreover, while single-photon qubits may be processed directly, "brighter" logical qubits may be embedded in individual oscillator modes, using so-called bosonic codes, for an in-principle fault-tolerant processing. In this work, we show how elements of all-optical, universal, and fault-tolerant quantum computation can be implemented using only beam splitters together with single-mode cubic phase gates in reasonable numbers, and possibly offline squeezed-state or single-photon resources. Our approach is based on a novel decomposition technique combining exact gate decompositions and approximate trotterization. This allows for efficient decompositions of certain nonlinear continuousvariable multi-mode gates into the elementary gates, where the few cubic gates needed may even be weak or all identical, thus facilitating potential experiments. The final gate operations include two-mode controlled phase rotation and three-mode Rabi-type Hamiltonian gates, which are shown to be employable for realizing high-fidelity single-photon two-qubit entangling gates or, as a bosoniccode example, creating high-quality Gottesman-Kitaev-Preskill states. We expect our method of general use with various applications, including those that rely on quartic Kerr-type interactions.

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Section: A Exact Decomposition Of Cubic Multi-mode Gatesmentioning

confidence: 99%

All-optical quantum computing using cubic phase gates

Budinger¹,

Furusawa²,

Loock³

2022

Preprint

View full text Add to dashboard Cite

show abstract

“…The strong coupling between the oscillator and the qubit can be accurately described by the Rabi Hamiltonian which does not invoke the rotating-wave approximation (RWA) as is done for the conventional Jaynes-Cummings (JC) Hamiltonian. Such a Rabi Hamiltonian has been shown to enable the preparation of different CV quantum states [61,62], the construction of CV quantum gates [63], slowing down the decoherence of CV states [64], conversion of the states between oscillators and qubits [65], and the realization of certain phase transitions [66,67]. These Rabi interactions also appear to be favorable to quantum interferometry of photon scattering events, termed cat-state spectroscopy as demonstrated on single qubits on a trapped ion crystal [68,69].…”

mentioning

confidence: 99%

Quantum Rabi interferometry of motion and radiation

Park¹,

Hastrup²,

Marek³

et al. 2022

Preprint

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The precise determination of a displacement of a mechanical oscillator or a microwave field in a predetermined direction in phase space can be carried out with trapped ions or superconducting circuits, respectively, by coupling the oscillator with ancilla qubits. Through that coupling, the displacement information is transferred to the qubits which are then subsequently read out. However, unambiguous estimation of displacement in an unknown direction in the phase space has not been attempted in such oscillator-qubit systems. Here, we propose a hybrid oscillator-qubit interferometric setup for the unambiguous estimation of phase space displacements in an arbitrary direction, based on feasible Rabi interactions beyond the rotating-wave approximation. Using such a hybrid Rabi interferometer for quantum sensing, we show that the performance is superior to the ones attained by single-mode estimation schemes and a conventional interferometer based on Jaynes-Cummings interactions. Moreover, we find that the sensitivity of the Rabi interferometer is independent of the thermal occupation of the oscillator mode, and thus cooling it to the ground state before sensing is not required. We also perform a thorough investigation of the effect of qubit dephasing and oscillator thermalization. We find the interferometer to be fairly robust, outperforming different benchmark estimation schemes even for large dephasing and thermalization. I. INTRODUCTIONQuantum sensing is about estimating unknown processes of interest using a finite ensemble of probes and detectors with a sensitivity that goes beyond the reach of classical sensing [1-5]. Historically, optical probes have been at the center of this field due to the experimental accessibility of lasers and non-classical light resources, high-efficiency detectors, and the strong robustness of light to external noise sources [6][7][8][9]. Quantum optical interferometers exploit the interference between a probe and a reference beam to detect weak signals [10], a prominent example being the detection of gravitational waves from black hole mergers [11,12]. A similar approach can be adopted for microwave traveling waves [13], microwave cavity fields [14], matter waves [15,16], between light and atomic ensembles [17,18], and optomechanics [19][20][21].Numerous sensing proposals use quantum non-Gaussian states as probes for improved estimation of phase and displacement [22][23][24]. For example, quantum displacement sensing has been performed with Fock states and non-Gaussian superpositions of Fock states of the phononic modes of trapped ions [25,26]. Similarly, for superconducting circuits, the preparation of microwave Fock states and their superpositions has been recently mastered [27][28][29][30] as well as the preparation of non-Gaussian acoustic modes of a quartz crystal [31], which can be also used for measuring displacements. Superconducting transmon has been recently used for sensing magnons [32][33][34], search for dark matter [35], microwave radiometry [36][37][38] including sensing...

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Slowing quantum decoherence of oscillators by hybrid processing

et al. 2022

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Quantum information encoded into the superposition of coherent states is an illustrative representation of practical applications of macroscopic quantum coherence possessing. However, these states are very sensitive to energy loss, losing their non-classical aspects of coherence very rapidly. An available deterministic strategy to slow down this decoherence process is to apply a Gaussian squeezing transformation prior to the loss as a protective step. Here, we propose a deterministic hybrid protection scheme utilizing strong but feasible interactions with two-level ancillas immune to spontaneous emission. We verify the robustness of the scheme against the dephasing of qubit ancilla. Our scheme is applicable to complex superpositions of coherent states in many oscillators, and remarkably, the robustness to loss is enhanced with the amplitude of the coherent states. This scheme can be realized in experiments with atoms, solid-state systems, and superconducting circuits.

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Universal Unitary Transfer of Continuous-Variable Quantum States into a Few Qubits

Cited by 5 publications

References 15 publications

All-optical quantum computing using cubic phase gates

All-optical quantum computing using cubic phase gates

Quantum Rabi interferometry of motion and radiation

Slowing quantum decoherence of oscillators by hybrid processing

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