arXiv subjects

Mohammad Mirhosseini

Publications and source records attributed to Mohammad Mirhosseini.

At least 19 recordsLinked to original sources

arXiv2026

Dynamic stimulated emission for deterministic addition and subtraction of propagating photons

Photon subtraction and addition are essential non-Gaussian processes in quantum optics, where conventional methods using linear optics and number-resolving detection often suffer from low success probability. Here, we introduce the concept of \textit{dynamic stimulated emission}, whereby a quantum emitter undergoes stimulated emission with a time-dependent coupling. Despite interacting with a multimode photon field, we show that, for both two- and three-level emitters, their dynamics can mimic that of a single-mode Jaynes-Cummings model. This feature can be used to deterministically add or subtract a photon while maintaining a single propagating optical mode. We provide semi-analytic solutions to this problem for Fock states, enabling deterministic and unconditional photon addition and subtraction with fidelity ${\cal F}>0.996$. Our semi-analytic solutions are provided for both dynamically coupled two-level systems and for three-level systems whose dynamical coupling is controlled by a coherent laser drive. Moving beyond individual Fock states, we further showcase the ability to subtract and add single photons to photon-number superposition states. We show that Schr{ö}dinger cat states can be prepared from squeezed vacuum input via cascaded subtraction or cascaded addition. Finally, we show that our photon-addition process can be used to add a photon to any squeezed and displaced state with high success probability and fidelity ${\cal F}>0.99$, thereby potentially converting quantum emitters from single-photon sources to sources of single-photon-added Gaussian states without the need for inline squeezing. Our protocols provide a path towards integrating quantum emitters to construct efficient sources of single-mode non-Gaussian light beyond single photons.

quant-ph↗

arXiv2026

Many-body quantum optics in a cascaded chiral network

Chiral quantum emitters interact with light only in one propagation direction, allowing them to be linked into cascaded systems in which photons mediate ordered, long-range interactions. Such systems are predicted to host novel regimes of many-body physics of light and matter. Exploring these regimes requires arrays of identical quantum emitters with directional, low-loss coupling to guided photons, a combination that has thus far remained experimentally out of reach. Here we realize a cascaded network of superconducting qubits using an architecture that overcomes these bottlenecks. We implement a four-qubit chain spanning two modules, with separations ranging from millimeters to half a meter, and exploit the shared waveguide as a dissipative resource to stabilize reconfigurable entanglement, reaching a genuinely multipartite regime unavailable in reciprocal baths. By scattering weak pulses off the chain, we observe photons sorted in time by photon number, a signature of the strong photon-photon interactions mediated by the emitters. Together, these results provide experimental access to many-body light-matter regimes that are beyond the reach of reciprocal systems.

quant-ph↗

arXiv2026

Piezoelectric resonators in thin-film barium titanate from room temperature to millikelvin

Ferroelectric materials, with their strong nonlinearities, underpin key technologies across radio-frequency (RF) signal processing, optical communications, and emerging quantum systems. Barium titanate (BTO) is a notable example, combining strong piezoelectric and electro-optic responses. While bulk BTO has been studied for decades, the piezoelectric properties of its recently available thin films, and their behavior at the millikelvin temperatures relevant to quantum hardware, remain largely unexplored. Here, we fabricate and characterize surface acoustic wave (SAW) resonators on thin-film BTO. The measured devices exhibit high electromechanical coupling (k2eff 0.14 at 5.2 GHz) and operate up to 7.8 GHz. From these measurements, combined with finite-element modeling of the multi-domain microstructure, we extract an effective piezoelectric coefficient d33eff of 53 pC/N, comparable to bulk BTO. Exploiting the intrinsic ferroelectricity, we further demonstrate low-voltage switching with a fast (100 ns) response, attractive for reconfigurable RF front-ends and parametric amplifiers. Extending these measurements to millikelvin temperatures, we find that the piezoelectric response persists, with d33eff 19 pC/N, pointing to the potential of BTO for piezoelectric coupling in superconducting quantum circuits. These results position thin-film BTO as a promising piezoelectric platform for both classical and quantum information technologies.

physics.app-ph↗

arXiv2024

A mechanical quantum memory for microwave photons

Long-lived mechanical oscillators are actively pursued as critical resources for quantum storage, sensing, and transduction. However, achieving deterministic quantum control while limiting mechanical dissipation remains a persistent challenge. Here, we demonstrate strong coupling between a transmon superconducting qubit and an ultra-long-lived nanomechanical oscillator ($T_\text{1} \approx 25 \text{ ms}$ at 5 GHz, $Q \approx 0.8 \times 10^9$) by leveraging the low acoustic loss in silicon and phononic bandgap engineering. The qubit-oscillator system achieves large cooperativity ($C_{T_1}\approx 1.5\times10^5$, $C_{T_2}\approx 150$), enabling the generation of non-classical states and the investigation of mechanisms underlying mechanical decoherence. We show that dynamical decoupling$\unicode{x2014}$implemented through the qubit$\unicode{x2014}$can mitigate decoherence, leading to a mechanical coherence time of $T_2\approx 1 \text{ ms}$. These findings extend the exceptional storage capabilities of mechanical oscillators to the quantum regime, putting them forward as compact bosonic elements for future applications in quantum computing and metrology.

quant-ph↗

arXiv2024

Quantum-enabled continuous microwave-to-optics frequency conversion

A quantum interface between microwave and optical photons is essential for entangling remote superconducting quantum processors. To preserve fragile quantum states, a transducer must operate efficiently while generating less than one photon of noise referred to its input. Here, we present a platform that meets these criteria, utilizing a combination of electrostatic and optomechanical interactions in devices made entirely from crystalline silicon. This platform's small mechanical dissipation and low optical absorption enable ground-state radiative cooling, resulting in quantum-enabled operation with a continuous laser drive. Under the optimal settings for high efficiency (low noise), we measure an external efficiency of $2.2\%$ ($0.47\%$) and an input-referred added noise of $0.94$ ($0.58$) in microwave-to-optics conversion. We quantify the transducer throughput using the efficiency-bandwidth product, finding it exceeds previous demonstrations with similar noise performance by approximately two orders of magnitude, thereby paving a practical path to interconnecting remote superconducting qubits.

quant-ph↗

arXiv2024

Stabilizing remote entanglement via waveguide dissipation

Distributing entanglement between remote sites is integral to quantum networks. Here, we demonstrate the autonomous stabilization of remote entanglement between a pair of non-interacting superconducting qubits connected by an open waveguide on a chip. In this setting, the interplay between a classical continuous drive - supplied through the waveguide - and dissipation into the waveguide stabilizes the qubit pair in a dark state, which, asymptotically, takes the form of a Bell state. We use field-quadrature measurements of the photons emitted to the waveguide to perform quantum state tomography on the stabilized states, where we find a concurrence of $0.504^{+0.007}_{-0.029}$ in the optimal setting with a stabilization time constant of 56 $\pm$ 4 ns. We examine the imperfections within our system and discuss avenues for enhancing fidelities and achieving scalability in future work. The decoherence-protected, steady-state remote entanglement offered via dissipative stabilization may find applications in distributed quantum computing, sensing, and communication.

quant-ph↗

arXiv2022

Resonance fluorescence of a chiral artificial atom

We demonstrate a superconducting artificial atom with strong unidirectional coupling to a microwave photonic waveguide. Our artificial atom is realized by coupling a transmon qubit to the waveguide at two spatially separated points with time-modulated interactions. Direction-sensitive interference arising from the parametric couplings in our scheme results in a non-reciprocal response, where we measure a forward/backward ratio of spontaneous emission exceeding 100. We verify the quantum nonlinear behavior of this artificial chiral atom by measuring the resonance fluorescence spectrum under a strong resonant drive and observing well-resolved Mollow triplets. Further, we demonstrate chirality for the second transition energy of the artificial atom and control it with a pulse sequence to realize a qubit-state-dependent non-reciprocal phase on itinerant photons. Our demonstration puts forth a superconducting hardware platform for the scalable realization of several key functionalities pursued within the paradigm of chiral quantum optics, including quantum networks with all-to-all connectivity, driven-dissipative stabilization of many-body entanglement, and the generation of complex non-classical states of light.

quant-ph↗

arXiv2022

Electro-optic transduction in silicon via GHz-frequency nanomechanics

Interfacing electronics with optical fiber networks is key to the long-distance transfer of classical and quantum information. Piezo-optomechanical transducers enable such interfaces by using GHz-frequency acoustic vibrations as mediators for converting microwave photons to optical photons via the combination of optomechanical and piezoelectric interactions. However, despite successful demonstrations, efficient piezo-optomechanical transduction remains out of reach due to the challenges associated with hybrid material integration and increased loss from piezoelectric materials when operating in the quantum regime. Here, we demonstrate an alternative approach in which we actuate 5-GHz phonons in a conventional silicon-on-insulator platform. In our experiment, microwave photons resonantly drive a phononic crystal oscillator via the electrostatic force realized in a charge-biased narrow-gap capacitor. The mechanical vibrations are subsequently transferred via a phonon waveguide to an optomechanical cavity, where they transform into optical photons in the sideband of a pump laser field. Operating at room temperature and atmospheric pressure, we measure a microwave-to-optical photon conversion efficiency of $1.8 \times 10^{-7}$ in a 3.3 MHz bandwidth, and demonstrate efficient phase modulation with a half-wave voltage of $V_π= 750 $ mV. Our results mark a stepping stone towards quantum transduction with integrated devices made from crystalline silicon, which promise efficient high-bandwidth operation, and integration with superconducting qubits. Additionally, the lack of need for piezoelectricity or other intrinsic nonlinearities makes our approach adaptable to a wide range of materials for potential applications beyond quantum technologies.

physics.optics↗

arXiv2022

Strong kinetic-inductance Kerr nonlinearity with titanium nitride nanowires

Thin films of disordered superconductors such as titanium nitride (TiN) exhibit large kinetic inductance (KI), high critical temperature, and large quality factors at the single-photon level. KI nonlinearity can be exploited as an alternative to Josephson junctions for creating novel nonlinear quantum devices with the potential to operate at higher frequencies and at elevated temperatures. We study a means of magnifying KI nonlinearity by confining the current density of resonant electromagnetic modes in nanowires with a small volume $V \simeq 10^{-4}\text{um}^3$. Using this concept, we realize microwave-frequency Kerr cavities with a maximum Kerr-shift per photon of $K/2π= 123.5 \pm 3$ kHz and report a nonlinearity-to-linewidth ratio $K/γ= 21\%$. With improved design, our devices are expected to approach the regime of strong quantum nonlinearity in the millimeter-wave spectrum.

quant-ph↗

arXiv2022

A quantum electromechanical interface for long-lived phonons

Controlling long-lived mechanical oscillators in the quantum regime holds promises for quantum information processing. Here, we present an electromechanical system capable of operating in the GHz-frequency band in a silicon-on-insulator platform. Relying on a novel driving scheme based on an electrostatic field and high-impedance microwave cavities based on TiN superinductors, we are able to demonstrate a parametrically-enhanced electromechanical coupling of ${g/2 π} = 1.1$ MHz, sufficient to enter the strong-coupling regime with a cooperativity of $\mathcal{C} = 1200$. The absence of piezoelectric materials in our platform leads to long mechanical lifetimes, finding intrinsic values up to $τ_\text{d} = 265~ μ$s ($Q = 8.4 \times {10}^6$ at $ω_\mathrm{m}/2π= 5$ GHz) measured at low-phonon numbers and millikelvin temperatures. Despite the strong parametric drives, we find the cavity-mechanics system in the quantum ground state by performing sideband thermometry measurements. Simultaneously achieving ground-state operation, long mechanical lifetimes, and strong coupling sets the stage for employing silicon electromechanical resonators as memory elements and transducers in hybrid quantum systems, and as a tool for probing the origins of acoustic loss in the quantum regime.

quant-ph↗

arXiv2022

Deep sub-wavelength localization of light and sound in dielectric resonators

Optomechanical crystals provide coupling between phonons and photons by confining them to commensurate wavelength-scale dimensions. We present a new concept for designing optomechanical crystals capable of achieving unprecedented coupling rates by confining optical and mechanical waves to deep sub-wavelength dimensions. Our design is based on a dielectric bowtie unit cell with an effective optical/mechanical mode volume of $7.6 \times 10^{-3} {(λ/n_{\textrm{Si}})}^3$/$ 1.2 \times 10^{-3} {λ_{\textrm{mech}}}^3$. We present results from numerical modeling, indicating a single-photon optomechanical coupling of 2.2 MHz with experimentally viable parameters. Monte Carlo simulations are used to demonstrate the design's robustness against fabrication disorder.

physics.optics↗

arXiv2021

Initial Design of a W-band Superconducting Kinetic Inductance Qubit (Kineticon)

Superconducting qubits are widely used in quantum computing research and industry. We describe a superconducting kinetic inductance qubit (and introduce the term Kineticon to describe it) operating at W-band frequencies with a nonlinear nanowire section that provides the anharmonicity required for two distinct quantum energy states. Operating the qubits at higher frequencies may relax the dilution refrigerator temperature requirements for these devices and paves the path for multiplexing a large number of qubits. Millimeter-wave operation requires superconductors with relatively high $T_c$, which implies high gap frequency, 2$Δ/h$, beyond which photons break Cooper pairs. For example, NbTiN with $T_c =15\,\text{K}$ has a gap frequency near 1.4 THz, which is much higher than that of aluminum (90 GHz), allowing for operation throughout the millimeter-wave band. Here we describe a design and simulation of a W-band Kineticon qubit embedded in a 3-D cavity. We perform classical electromagnetic calculations of the resulting field distributions.

quant-ph↗

arXiv2020

Quantum electrodynamics in a topological waveguide

While designing the energy-momentum relation of photons is key to many linear, non-linear, and quantum optical phenomena, a new set of light-matter properties may be realized by employing the topology of the photonic bath itself. In this work we investigate the properties of superconducting qubits coupled to a metamaterial waveguide based on a photonic analog of the Su-Schrieffer-Heeger model. We explore topologically-induced properties of qubits coupled to such a waveguide, ranging from the formation of directional qubit-photon bound states to topology-dependent cooperative radiation effects. Addition of qubits to this waveguide system also enables direct quantum control over topological edge states that form in finite waveguide systems, useful for instance in constructing a topologically protected quantum communication channel. More broadly, our work demonstrates the opportunity that topological waveguide-QED systems offer in the synthesis and study of many-body states with exotic long-range quantum correlations.

quant-ph↗

arXiv2020

Quantum transduction of optical photons from a superconducting qubit

Bidirectional conversion of electrical and optical signals lies at the foundation of the global internet. Such converters are employed at repeater stations to extend the reach of long-haul fiber optic communication systems and within data centers to exchange high-speed optical signals between computers. Likewise, coherent microwave-to-optical conversion of single photons would enable the exchange of quantum states between remotely connected superconducting quantum processors, a promising quantum computing hardware platform. Despite the prospects of quantum networking, maintaining the fragile quantum state in such a conversion process with superconducting qubits has remained elusive. Here we demonstrate the conversion of a microwave-frequency excitation of a superconducting transmon qubit into an optical photon. We achieve this using an intermediary nanomechanical resonator which converts the electrical excitation of the qubit into a single phonon by means of a piezoelectric interaction, and subsequently converts the phonon to an optical photon via radiation pressure. We demonstrate optical photon generation from the qubit with a signal-to-noise greater than unity by recording quantum Rabi oscillations of the qubit through single-photon detection of the emitted light over an optical fiber. With proposed improvements in the device and external measurement set-up, such quantum transducers may lead to practical devices capable of realizing new hybrid quantum networks, and ultimately, distributed quantum computers.

quant-ph↗

arXiv2020

Collapse and Revival of an Artificial Atom Coupled to a Structured Photonic Reservoir

A structured electromagnetic reservoir can result in novel dynamics of quantum emitters. In particular, the reservoir can be tailored to have a memory of past interactions with emitters, in contrast to memory-less Markovian dynamics of typical open systems. In this Article, we investigate the non-Markovian dynamics of a superconducting qubit strongly coupled to a superconducting slow-light waveguide reservoir. Tuning the qubit into the spectral vicinity of the passband of this waveguide, we find non-exponential energy relaxation as well as substantial changes to the qubit emission rate. Further, upon addition of a reflective boundary to one end of the waveguide, we observe revivals in the qubit population on a timescale 30 times longer than the inverse of the qubit's emission rate, corresponding to the round-trip travel time of an emitted photon. By tuning of the qubit-waveguide interaction strength, we probe a crossover between Markovian and non-Markovian qubit emission dynamics. These attributes allow for future studies of multi-qubit circuits coupled to structured reservoirs, in addition to constituting the necessary resources for generation of multiphoton highly entangled states.

quant-ph↗

arXiv2019

Two-Dimensional Optomechanical Crystal Cavity with High Quantum Cooperativity

Optomechanical systems offer new opportunities in quantum information processing and quantum sensing. Many solid-state quantum devices operate at millikelvin temperatures -- however, it has proven challenging to operate nanoscale optomechanical devices at these ultralow temperatures due to their limited thermal conductance and parasitic optical absorption. Here, we demonstrate a two-dimensional optomechanical crystal resonator capable of achieving large cooperativity $C$ and small effective bath occupancy $n_b$, resulting in a quantum cooperativity $C_{\text{eff}}\equiv C/n_b \approx 1.3 > 1$ under continuous-wave optical driving. This is realized using a two-dimensional phononic bandgap structure to host the optomechanical cavity, simultaneously isolating the acoustic mode of interest in the bandgap while allowing heat to be removed by phonon modes outside of the bandgap. This achievement paves the way for a variety of applications requiring quantum-coherent optomechanical interactions, such as transducers capable of bi-directional conversion of quantum states between microwave frequency superconducting quantum circuits and optical photons in a fiber optic network.

quant-ph↗

arXiv2019

Using all transverse degrees of freedom in quantum communications based on a generic mode sorter

The dimension of the state space for information encoding offered by the transverse structure of light is usually limited by the finite size of apertures. The widely used orbital angular momentum (OAM) number of Laguerre-Gaussian (LG) modes in free-space communications cannot achieve the theoretical maximum transmission capacity unless the radial degree of freedom is multiplexed into the protocol. While the methodology to sort the radial quantum number has been developed, the application of radial modes in quantum communications requires an additional ability to efficiently measure the superposition of LG modes in the mutually unbiased basis. Here we develop and implement a generic mode sorter that is capable of sorting the superposition of LG modes through the use of a mode converter. As a consequence, we demonstrate an 8-dimensional quantum key distribution experiment involving all three transverse degrees of freedom: spin, azimuthal, and radial quantum numbers of photons. Our protocol presents an important step towards the goal of reaching the capacity limit of a free-space link and can be useful to other applications that involve spatial modes of photons.

physics.optics↗

arXiv2019

Quantum-limited estimation of the axial separation of two incoherent point sources

Improving axial resolution is crucial for three-dimensional optical imaging systems. Here we present a scheme of axial superresolution for two incoherent point sources based on spatial mode demultiplexing. A radial mode sorter is used to losslessly decompose the optical fields into a radial mode basis set to extract the phase information associated with the axial positions of the point sources. We show theoretically and experimentally that, in the limit of a zero axial separation, our scheme allows for reaching the quantum Cramér-Rao lower bound and thus can be considered as one of the optimal measurement methods. Unlike other superresolution schemes, this scheme does not require neither activation of fluorophores nor sophisticated stabilization control. Moreover, it is applicable to the localization of a single point source in the axial direction. Our demonstration can be useful to a variety of applications such as far-field fluorescence microscopy.

physics.optics↗