Q. Quraishi

University of Maryland, College Park, College Park, MD, United States

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Publications (12)23.83 Total impact

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    ABSTRACT: We stabilize a chosen radiofrequency beat note between two optical fields derived from the same mode-locked laser pulse train, in order to coherently manipulate quantum information. This scheme does not require access or active stabilization of the laser repetition rate. We implement and characterize this external lock, in the context of two-photon stimulated Raman transitions between the hyperfine ground states of trapped 171-Yb+ quantum bits.
    Optics Letters 12/2013; 39(11). · 3.39 Impact Factor
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    ABSTRACT: We demonstrate a simple pulse shaping technique designed to improve the fidelity of spin-dependent force operations commonly used to implement entangling gates in trapped ion systems. This extension of the Mølmer-Sørensen gate can theoretically suppress the effects of certain frequency and timing errors to any desired order and is demonstrated through Walsh modulation of a two qubit entangling gate on trapped atomic ions. The technique is applicable to any system of qubits coupled through collective harmonic oscillator modes.
    Physical Review Letters 07/2012; 109(2):020503. · 7.94 Impact Factor
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    ABSTRACT: Trapped ions entangled via photonic interactions are promising avenues for quan-tum information processing. Here, we report advances towards combining photonic gates be-tween distant ions with Coulombic gates between nearby ions to demonstrate scalable quantum networks.
    10/2011;
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    ABSTRACT: Control of spin dependent forces is important for generating entanglement and realizing quantum simulations in trapped ion systems. Here we propose and implement a composite pulse sequence based on the Molmer-Sorenson gate to decrease gate infidelity due to frequency and timing errors. The composite pulse sequence uses an optical frequency comb to drive Raman transitions simultaneously detuned from trapped ion transverse motional red and blue sideband frequencies. The spin dependent force displaces the ions in phase space, and the resulting spin-dependent geometric phase depends on the detuning. Voltage noise on the rf electrodes changes the detuning between the trapped ions' motional frequency and the laser, decreasing the fidelity of the gate. The composite pulse sequence consists of successive pulse trains from counter- propagating frequency combs with phase control of the microwave beatnote of the lasers to passively suppress detuning errors. We present the theory and experimental data with one and two ions where a gate is performed with a composite pulse sequence. This work supported by the U.S. ARO, IARPA, the DARPA OLE program, the MURI program; the NSF PIF Program; the NSF Physics Frontier Center at JQI; the European Commission AQUTE program; and the IC postdoc program administered by the NGA.
    06/2011;
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    ABSTRACT: Quantum information processing with trapped ions has traditionally involved state preparation, manipulation (eg. quantum gates) and detection using CW lasers. Quantum gates implemented with ions typically involve optical Raman transitions between two atomic levels. An optical frequency comb, emitted by a pulsed laser, is an excellent tool for bridging atomic frequency differences. Previously, we demonstrated quantum gates and separately, ultrafast spin manipulation, using pulsed lasers [1,2]. Unlike the CW case, employing pulsed lasers has the marked advantage of both low spontaneous emission and low AC Stark shifts, because the high powers available from pulsed lasers allow for larger detunings from optical resonance. Here, we show both experimentally and theoretically the scaling of the differential Stark shift with detuning (6 THz to 20 THz) of the Raman fields, achieving values of 10-3 of the Rabi frequency. [1] D. Hayes, et al., Phys. Rev. Lett. 104, 140501 (2010) [2] W. C. Campbell, et al., Phys. Rev. Lett. 105, 090502 (2010). *Currently NRC postdoc with SEDD, ARL, Adelphi, MD. Support: DARPA OLE under ARO contract, IARPA under ARO contract, NSF PIF Program, NSF PFC at JQI and *IC Postdoc administered by the NGA.
    03/2011;
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    ABSTRACT: We demonstrate single-qubit operations on a trapped atom hyperfine qubit using a single ultrafast pulse from a mode-locked laser. We shape the pulse from the laser and perform a π rotation of the qubit in less than 50 ps with a population transfer exceeding 99% and negligible effects from spontaneous emission or ac Stark shifts. The gate time is significantly shorter than the period of atomic motion in the trap (Ω(Rabi)/ν(trap)>10(4)), demonstrating that this interaction takes place deep within the strong excitation regime.
    Physical Review Letters 08/2010; 105(9):090502. · 7.94 Impact Factor
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    ABSTRACT: We demonstrate the use of an optical frequency comb to coherently control and entangle atomic qubits. A train of off-resonant ultrafast laser pulses is used to efficiently and coherently transfer population between electronic and vibrational states of trapped atomic ions and implement an entangling quantum logic gate with high fidelity. This technique can be extended to the high field regime where operations can be performed faster than the trap frequency. This general approach can be applied to more complex quantum systems, such as large collections of interacting atoms or molecules.
    Physical Review Letters 04/2010; 104(14):140501. · 7.94 Impact Factor
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    ABSTRACT: The spectral purity and large bandwidth of pulsed lasers makes them attractive candidates for precision control of multi-level atomic systems. We use a train of off resonant picosecond pulses from a mode-locked laser to drive stimulated Raman transitions between the hyperfine levels (˜10 GHz spacing) of trapped ytterbium ions and to cool to the quantum ground state of motion. By simultaneously addressing the spin and the motion of trapped ions using a train of laser pulses, we apply spin-dependent forces to create a single-ion Schrodinger cat state and implement a gate between two trapped ions to entangle their spins [1]. We also use high-intensity pulses to demonstrate fast (
    03/2010;
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    ABSTRACT: We describe an experiment to achieve ultrafast qubit operations on trapped <sup>171</sup>Yb<sup>+</sup> ions. We plan to use a series of short optical pulses to perform bit rotations and multi-bit entangling gates independent of ion temperature.
    Lasers and Electro-Optics, 2009 and 2009 Conference on Quantum electronics and Laser Science Conference. CLEO/QELS 2009. Conference on; 07/2009
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    ABSTRACT: Ultrashort light pulses are an attractive tool for trapped ion quantum information processing. High pulse intensity permits far-detuned (>10 nm) operation, where decoherence from differential AC Stark shifts and spontaneous emission is suppressed. Short pulse duration allows interaction times shorter than a trap oscillation, circumventing the need for cooling to the Lamb-Dicke limit. We describe an experiment with trapped ^171Yb^+ using a vanadate laser (˜10 ps pulses at 355 nm). Since the single pulse bandwidth exceeds the S1/2 hyperfine splitting, coherent Raman transitions between qubit states should be possible. This is in contrast to our previous work [1] with near-resonant pulses that coherently transfer population to the P-state. It should also be possible to use a series of multiple pulses to impart spin-dependent forces. By controlling the pulse timing and phase we could then entangle multiple ions in a temperature insensitive manner [2,3]. [1] Madsen et al., PRL 97, 040505 (2006). [2] Garc'ia-Ripoll et al., PRL 91, 157901 (2003). [3] Duan, PRL 93, 100502 (2004).
    05/2009;
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    ABSTRACT: Recent work in coherent transfer of atomic quantum states demonstrated the novel integration of ultrashort pulsed lasers with trapped ions [1]. Building on this work, we propose an experimental scheme whereby a sequence of optical pulses is used for quantum state manipulation. Specifically, we envisage trapping a single ytterbium ion in a linear trap and then, using a series of nonresonant optical pulses, we plan on individually addressing its hyperfine qubit state [2]. By controlling the timing, phases and intensities between successive pulses we can optimize the fidelity of the qubit gate. Given a 10 ps pulse duration laser, centered at 355 nm (14 nm from resonance at 369 nm) with 4 W average power, we expect two optical pulses to be sufficient to perform a single qubit rotation. Additionally, we expect that by using counter propagating pulses having well defined relative RF frequency shifts, we can impart controllable spin-dependent forces. These results are relevant for motional or temporal gates involving multiple ions. [1] S. Olmschenk, et. al., Science (2009). [2] J. J. Garcia-Ripoll, et. al., Phys. Rev. Lett. 91, 157901 (2003).
    05/2009;
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    ABSTRACT: We demonstrate a simple pulse shaping technique designed to improve the fidelity of the spin-dependent force operations that are now commonly used to implement entangling gates in trapped ion systems. This extension of the M{\o}lmer-S{\o}rensen gate can theoretically suppress the effects of certain frequency and timing errors to any desired order and is demonstrated using a single ion interacting with a mode-locked pulsed laser. The technique is applicable to any system of qubits coupled through collective harmonic oscillator modes.