Debbie Leung - Academia.edu (original) (raw)

Papers by Debbie Leung

Physical Review Letters, 2014

Privacy is a fundamental feature of quantum mechanics. A coherently transmitted quantum state is ... more Privacy is a fundamental feature of quantum mechanics. A coherently transmitted quantum state is inherently private. Remarkably, coherent quantum communication is not a prerequisite for privacy: there are quantum channels that are too noisy to transmit any quantum information reliably that can nevertheless send private classical information. Here, we ask how much private classical information a channel can transmit if it has little quantum capacity. We present a class of channels N(d) with input dimension d(2), quantum capacity Q(N(d)) ≤ 1, and private capacity P(N(d)) = log d. These channels asymptotically saturate an interesting inequality P(N) ≤ (1/2)[log d(A) + Q(N)] for any channel N with input dimension d(A) and capture the essence of privacy stripped of the confounding influence of coherence.

Physical Review Letters, 2009

Physical Review Letters, 2004

IEEE Transactions on Information Theory, 2003

Communications in Mathematical Physics, 2012

Lecture Notes in Computer Science, 2005

Physical review letters, Jan 28, 2003

We characterize the class of remote state preparation (RSP) protocols that use only forward class... more We characterize the class of remote state preparation (RSP) protocols that use only forward classical communication and entanglement, deterministically prepare an exact copy of a general state, and do so obliviously-without leaking further information about the state to the receiver. We prove that any such protocol can be modified to require from the sender only a single specimen of the state, without increasing the classical communication cost. This implies Lo's conjectured lower bound on the cost for these protocols. We relate our RSP protocols to the private quantum channels and establish a one-to-one correspondence between them.

Imaging and Applied Optics, 2011

Abstract: Message authentication is a cryptographic task that allows the receiver to reject a mes... more Abstract: Message authentication is a cryptographic task that allows the receiver to reject a message that is forged or has been tampered with. A protocol to authenticate quantum messages was proposed by Barnum, Crépeau, Gottesman, Tapp, and Smith [1] and stand-alone security was proved. Here, we are concerned with universal composable security (which requires a protocol to be essentially indistinguishable from the ideal functionality and ensures overall security when the protocol is part of any larger scheme). We show that the protocol in [1] is universal ...

In quantum information theory, a capacity Q(χ) of a channel χ is a theoretical maximum of the rat... more In quantum information theory, a capacity Q(χ) of a channel χ is a theoretical maximum of the rate m/n that is achievable by some communication protocol that sends m-qubit information with n uses of the channel, where n tends to infinity. The above definition of Q is defined without auxiliary resources, and additional free classi- cal communication may increase the capacity. We use Q, Q1, QB, and Q2 to denote the quantum capacities of a quantum channel when unassisted, assisted by unlim- ited forward, backward, and two-way classical communi- cation, respectively. It was proved that classical forward communication alone does not increase the quantum ca- pacity of any channel; in other words Q(χ) = Q1(χ) for all channels χ (1). In contrast, Q2 is greater than Q for some channels (1). QB is also known to be greater than Q for some channels (2), but it has been an open question whether QB(χ) = Q2(χ) for all χ. We study the capacities of the quantum erasure chan- nel, which was first int...

Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, 1998

... In §2, we show how our techniques to create effective pure states can be understood using the... more ... In §2, we show how our techniques to create effective pure states can be understood using the notion of state labelling: attaching logical, spatial or temporal labels to the quantum state in such a way that a subspace within the mixed state can be identified and used for quantum ...

Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2013

Physical Review Letters, 2004

Physical Review Letters, 2004

Physical Review Letters, 2001

Physical Review Letters, 2014

Privacy is a fundamental feature of quantum mechanics. A coherently transmitted quantum state is ... more Privacy is a fundamental feature of quantum mechanics. A coherently transmitted quantum state is inherently private. Remarkably, coherent quantum communication is not a prerequisite for privacy: there are quantum channels that are too noisy to transmit any quantum information reliably that can nevertheless send private classical information. Here, we ask how much private classical information a channel can transmit if it has little quantum capacity. We present a class of channels N(d) with input dimension d(2), quantum capacity Q(N(d)) ≤ 1, and private capacity P(N(d)) = log d. These channels asymptotically saturate an interesting inequality P(N) ≤ (1/2)[log d(A) + Q(N)] for any channel N with input dimension d(A) and capture the essence of privacy stripped of the confounding influence of coherence.

Physical Review Letters, 2009

Physical Review Letters, 2004

IEEE Transactions on Information Theory, 2003

Communications in Mathematical Physics, 2012

Lecture Notes in Computer Science, 2005

Physical review letters, Jan 28, 2003

We characterize the class of remote state preparation (RSP) protocols that use only forward class... more We characterize the class of remote state preparation (RSP) protocols that use only forward classical communication and entanglement, deterministically prepare an exact copy of a general state, and do so obliviously-without leaking further information about the state to the receiver. We prove that any such protocol can be modified to require from the sender only a single specimen of the state, without increasing the classical communication cost. This implies Lo's conjectured lower bound on the cost for these protocols. We relate our RSP protocols to the private quantum channels and establish a one-to-one correspondence between them.

Imaging and Applied Optics, 2011

Abstract: Message authentication is a cryptographic task that allows the receiver to reject a mes... more Abstract: Message authentication is a cryptographic task that allows the receiver to reject a message that is forged or has been tampered with. A protocol to authenticate quantum messages was proposed by Barnum, Crépeau, Gottesman, Tapp, and Smith [1] and stand-alone security was proved. Here, we are concerned with universal composable security (which requires a protocol to be essentially indistinguishable from the ideal functionality and ensures overall security when the protocol is part of any larger scheme). We show that the protocol in [1] is universal ...

In quantum information theory, a capacity Q(χ) of a channel χ is a theoretical maximum of the rat... more In quantum information theory, a capacity Q(χ) of a channel χ is a theoretical maximum of the rate m/n that is achievable by some communication protocol that sends m-qubit information with n uses of the channel, where n tends to infinity. The above definition of Q is defined without auxiliary resources, and additional free classi- cal communication may increase the capacity. We use Q, Q1, QB, and Q2 to denote the quantum capacities of a quantum channel when unassisted, assisted by unlim- ited forward, backward, and two-way classical communi- cation, respectively. It was proved that classical forward communication alone does not increase the quantum ca- pacity of any channel; in other words Q(χ) = Q1(χ) for all channels χ (1). In contrast, Q2 is greater than Q for some channels (1). QB is also known to be greater than Q for some channels (2), but it has been an open question whether QB(χ) = Q2(χ) for all χ. We study the capacities of the quantum erasure chan- nel, which was first int...

Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, 1998

... In §2, we show how our techniques to create effective pure states can be understood using the... more ... In §2, we show how our techniques to create effective pure states can be understood using the notion of state labelling: attaching logical, spatial or temporal labels to the quantum state in such a way that a subspace within the mixed state can be identified and used for quantum ...

Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2013

Physical Review Letters, 2004

Physical Review Letters, 2004

Physical Review Letters, 2001